Prop walk: the blade at the top of its turn, ie 12 o'clock, gets a bit of end plate effect so gives a bit more side thrust as it passes through 12 o'clock (tip vortex is reduced at 12 o'clock). That's why you get the imbalance of side thrust. At least that's what I was taught getting my bachelors in nav. arch. Prop walk can vary depending on the flow into the prop also, which is affected by speed and hull shape. Prop walk is really noticeable on tugboats that have old style fixed props on a shaft. Number of blades... usually you want to keep the blade number not an even fraction of the engine cylinders to keep vibration down (can be exceptions). I.e. if your engine has 4 cylinders, having 3 blades is better than 2 or 4 blades. This is due to the additional side thrust of the 12 o'clock blade. If you have an even multiple of blades to cylinders, you tend to get a sync of a cylinder firing at the same time you get that extra side force on the shaft, which can cause a vibration. Good vid, brings back memories of my segment in school on prop design.
@Mission Gameliel Not when crossing oceans or night sailing or if you don't have enough room for the amount of panels needed for the amount of power required. Solar is good and very good, but it's not a solve all resource. If solar alone could do as you say then why solar is not fitting for all solar powered boats? More so the small day boats! (SOLAR HAS IT'S PLACE BUT IT'S NOT A SOLVE ALL)
Interesting your opinion on Kiwi Props. My experience, and the advice of the creator /manufacturer is lube on annual haul out! I've found that to be effective. I've not seen any erosion of the plastic blades, probably due to application of Prop Speed, so other than lube and prop speed I've had no maintenance issues in 6 years.
For a professional skipper who specialized in 12-day trips France to Ireland and back (64 trips total), a folding propeller him gave a good half-day gain on the whole trip. That meant one more stopover in a beautiful anchorage. Speed prediction formulas used in handicap systems assume a mix and upwind and downwind. A folding/feathering prop can make a 1.5-knot difference going upwind, easily. If the conditions are rough (against the current), that could even mean making it to destination vs. not.
The episode conveying the most 'wisdom' of all of your videos, imo. Very nice job, Herbie. Thank you for making that whole complicated issue/topic much clearer for me, and I'm guessing many others as well. Carry on, sailor.
Thanks! Great job. Third time I watched it. I’m going to emphasize P-factor. Airplane propellors get that in a high pitch. Boats with downward angled shafts get it even more. Propwalk will be most pronounced moving forward at low speed and high power and less so in reverse at low speed and low power. It just seems that it’s worse in reverse because of the pucker factor going into a slip and confusion over which way to turn the wheel. You guys are fantastic. Congratulations on your baby. And looking forward to more videos soon when you’re ready.
Super information and delivery. A natural teacher. It's very clear that you researched the subject in great depth and left no stone upturned. Everything was covered in a very considered and systematic manner. Each question that came to my mind was subsequently answered. Your technical knowledge is second to none and your channel is an excellent resource for all things sailing related. Thanks for taking the time to make the video and share the knowledge.
I just want to point out that a kiwi prop costs us$1500 for a 3 blades and OR $150 each blade when you change them. So I think the doctor just looked at the prices for extra blades ☺️
we have a 2 blade maxprop. Working on getting it rebuilt after using it problem free for 16 years. After taking it apart we found some damage inside, but it still worked without issue. Highly recommended, there is a trick to get it to feather, but you can tell when it is not feathered because the shaft spins and you can hear that on our boat. A quick pop into reverse and then neutral when the engine is off feathers the prop and the shaft stops spinning.
My boat came with an Atomic-4 engine with a folding prop (forget the brand). I liked the prop. I had no problems with it, and, though people said the prop walk would be worse, I had very little prop walk. Maintenance was about the same as a fixed prop. I converted to electric, and stayed with the folding prop for the first year. It was fine. After that, I got a used fixed prop at a very good price and wanted to test regen, so I changed the prop out. I noticed no appreciable change in sailing, and I can get a little (very little) regen when I sail >5 knots.
Great presentation! I don't know what date it was recorded but it may require updated especially regarding Kiwiprop pricing and blade composite which are (now) made using Dupont's Zylan HTN composite.
Thanks for the great video! We were on the fence about buying a folding propellor (we have a fixed prop). Got to the end of the video and your information about time saved was invaluable! We had estimated more lost time from dragging. We are going to stick with our fixed prop for now. Thanks again!
Herbie, HERBIE, hERBIE, I love ya man but u gotta get over this molecular plastic prop phobia. The first time i heard you say that (on a different video) i stopped in my tracts and backed up the video to be sure I heard you correctly. Later I found out you are a dentist which makes your comment seem so strange. As an engineer i can assure you your dental practice and day to day living not to mention the sunglasses on your head - contributes far more environmental pollution than plastic prop's microscopic ware in the frigging ocean. Sorry just couldn,t take it a 2nd time LOL. What makes me truly sad is we keep dumping trash in the ocean and it shows up on the shorelines of even the most remote islands. Love you and your sweet wife( and the birds) and have learned soo much about sailing from u 2. Keep up the good work!! PS Please listen to your wife about boat design especially on the artistic aspects of modifying a lady boat's rear end!!.😍
Haha! It’s all good. Every bit counts, and there is a lot going out there!! Thankfully they are starting to clean up the massive amounts of fishing equipment that is floating out there to help the oceans. I do love these props and think they are the best design of feathering/folding props!
Thank you for this great presentation, we are seriously considering changing our 2 blade fixed for either a flexofold or featherstream . Your explanation of prop walk is clear and easy to understand.
I have a two blade J Prop on our C34 MkII. It has a slight prop walk to port but feathers beautifully. I love your splicing videos. Really having problems finishing the knots on soft shackles though! I used to be a merchant mariner, and was taught that our prop walk was a result of the pressure differential between the blades. We were talking 18 foot diameter props !
🫨 18 foot!! Sailboat props must look like a handheld personal fan! Are you doing a button knot or the lovers knot? I like the lovers knot for a few reasons, but you can splice the tails of the knot into each other to make a single tail that is really handy for guiding the knot through the loop.
Great video Herbie. Again, your depth of knowledge and ability to convey it, is impressive. Prop walk is a pain... I owned a diesel powered Pearson with an offset propeller shaft to counter prop walk. Backing out of a slip with that offset shaft can be a major PITA depending on which way you needed to travel out of the slip and how much room you have backing out. If you back out with low speed, she walks. Some spots were tight enough a hi speed burst may not be advisable. Then of course, add the effect of currents! Like you, I paid real close attention to where and how I tied up. ;-) Well done video. Great explanation!
I have s two bladed folding prop on a standard propshaft. I get prop walk to starboard in reverse. I use this to advantage when coming into my slip because I can come almost abreast of my slip give full rudder to port and a stab of reverse and she'll pivot about her keel and I can then motor straight in. Simples!
Great job Herbie! I had a 2 blade ELICHE RADICE prop while sailing in the great lakes as part of preparing to head on down the erie canal then the icw and crossing oceans I decided to replace it with a 3 blade folding flex-o-fold. I ended up with the same speed but more torq. prop walk just a little less, under power. under sail I saw no difference. The big advantage I gained was coming into a dock was stopping distance, I would guess 1/4 boat length quicker. A fixed 14" prop under sail is like dragging a 5 gallon bucket behind the boat! But where you want the prop shaft to spin makes total sense. Bob
.......and then there is also the "variable pitch" propeller, usually controlled via hydraulics. It allows for very fine, infinite control, however it's a fairly complex system that is very expensive. Not usually found on the average yacht, but on the larger mega-yachts owned by billionaires (both sail and power). By the way Herby: You did an excellent job with your propeller lecture. You pretty much covered all the bases and offered a few compelling arguments for and against various types of props and their design characteristics. It appears you've done your homework. In fact you were so convincing, I'm thinking about getting rid of the prop and switching to oars (totally eliminates prop walk😁).
Nice interesting piece which covers it all. One point I'd like to add is I would serious miss my prop if it were not nice and close to the rudder blade. Manoeuvring does require experience as to which way the boat will turn when you put it in astern from standing still. BUT with the rudder close to the prop the walk is really small in ahead as you can blast water direct on to the rudder and make the boat turn any way you want almost immediately.
I know what you mean, it’s practically a stern thruster! I tried to dock a boat that the prop was far from the rudder and it was a very ungrateful event.
I own a Max-Prop and am very happy with it. In terms of maintenance, It requires grease every time I replace the anode. Prop walk is caused by the difference in water level on each side of the boat. We know that a right hand propeller walks the boat to port in reverse. In reverse, the top blade pushes water against the hull and the limited space rises the water level on the starboard side. The bottom blade has plenty of space to move the water hence lowers the water level on the port side. The difference in water levels pushes the boat sideways to port. The Max-Prop is 84% efficient in both directions. It is more efficient than a fixed blade in reverse. The Max-Prop won't stop rotating unless you stop the shaft from turning using the reverse gear. While it is turning, it can be used for the generator. When you are tired of the noise it creates inside the boat, you simply stop it. Cheers, Richard
The most efficient prop is one with the fewest blades (though one is not that practical), as big as possible, so it will have a smaller pitch to suit. Sailboat props are all about static thrust, think trying to make headway against a very strong wind.
I have had my yacht for 11 years, it came with a kiwi prop and it still has the same prop. I Antifoul the prop so maybe that is why my prop hasn’t desolved as you suggest. Works for me
The 2-blade Max-Prop model that you showed is supposedly capable of re-gen if you reverse just before turning off the engine. I don't have the capability to re-gen, but I know how to make the shaft turn if I want (provided I sail fast enough). Answering to one of your points about fixed blade propellers being always more efficient, I have to say the feathering mechanics ensure that the leading edge of the blade remains a leading edge when reversing. The featuring Max-Prop has amazing reverse performance.
I have a feathering 3 blade PYI style, love it. did not want the noise of the spinning fixed prop, did not want to deal with a shaft brake. Nothing wrong with prop walk, just have to know how and when to use it
Thank you very much. Comprehensive coverage on the subject and I learned something new to me which is Kiwi prop. But I must admit that by the 12:00 minute mark my head is spinning like a propeller trying to catch the torrent of terms rolling off your commentary. So I did what was best for me - listen, rewind, listen, stop and think, and head forward to the next segment. That's me, of course. Your knowledge is awesome.
Interesting opinion on Kiwi Props. My experience, and the advice of the creator /manufacturer is lube on annual haul out is essential! I've found that to be effective. I've not seen any erosion of the plastic blades, probably due to application of Prop Speed, so other than lube and prop speed I've had no maintenance issues in 6 years.
What an interesting discussion, about the opposite prop walk when drifting forward compared to when the boat is still. I can't say I have practically seen that, maybe because I am usually drifting very slowly when entering a slip. Reading the comments, it seems to be another illustration of the Dunning Kruger effect, overconfidence by those with less experience. Many of us sail on just a few boats regularly over a lifetime. In the end, learn how your boat responds and use that to advantage.
Great talk and real life examples! Couple of thoughts , the extra drag from the extra blades requires more hp because of the extra drag from the same dia blade, gets complicated obviously but Tugs with unlimited power have 5-6-7 blades. Prop walk in forward is compensated on a properly designed single engine yacht by having the prop shaft at a slight angle to center line 1-2 deg is typical. Love you point about port propwash in FWD and stb in reverse ! Some interesting looking yachts in that yard too! Cheers Warren
I have a U-8D that has twin props. It is actually an airplane, so they have prop walk of sorts as well. Some planes have counter rotating props and some don't. Mine does not. In fact if you lose a particular engine the torque effect may become more than the plane can handle and you get crash city. Though both props can be feathered with a control lever. With a boat I was always taught to put your rudder in the opposite direction of prop walk. That way if you can exactly control the boats speed and the prop speed you can get steerage in both directions at a relatively low relative boat speed.
I believe (hypothesize) that the reason prop walk works "backwards" when you have forward way on is that the wash is not acting on the keel but on the rudder until the boat is stopped, then it starts working on the keel. Just a thought from a guy with a full keel boat that (in reverse) walks to port like crazy!
I came across your video. Very informative, thanks for making it! One thing i do miss, or better I thought of seeing your video is the relation of drag/ loss of speed to the boat LWL and hullshape, cat or tri etc. For a small monohull a fixed large prop can make a difference of 0.5 to 1 knot. meaning 0.5 to 1 Nm per hour less distance. which is significant enough to change a setup. For a bigger vessel this number is reduced 0.1 to 0.2 knots or Nm/h. As for Propwalk...Single engine aircrafts experience this too, specially dragging tail aircrafts at low speed. (Prop is on an angle) Propwash is cause that the effect going forward is different than goin in reverse.
@@RiggingDoctor well thanks! Appreciate that! Wind and/or wind direction, weather, and sails is still a huge topic I've been trying to learn about. So many differences of opinion!
Regarding the kiwi prop, there are a couple of comments that I find difficult to take seriously. Life span, what is short or long? I drove a kiwi on a Harmony 34 between 2007 and 2018. No problems to report from that period. It is probably more important to make sure that these propellers are well lubricated and that the seals that hold the grease in place are changed at appropriate intervals. Wear of material in the blades? I haven't seen any of that at all, the last few years a layer of antifouling was put on the blades, it disappears with time but not so fast either. I see no reason why it wouldn't have worked for another ten years. And a big advantage, the blades angles can be adjusted to have the engine run on desired revs.
Good to know! I have friends in the Chesapeake Bay who have had to replace blades every 5 years or so. Makes me wonder what is in the Chesapeake! One friend barely moved his boat and the sun always hit one blade in particular. One blade disintegrated and it is assumed to have been the one that always had the sun hitting it while in the slip. Another friend (who first introduced me to kiwi props) told me about the polishing blades. He works at a boat yard in Baltimore and frequently would have to replace worn down blades on kiwi props. I really love them! Their simplicity, reliability, and adjustability make them the best non-fixed propeller in my opinion. I’m glad to know you didn’t have the blade polishing issue :) it might just be an issue in the bay.
Great vid as usual. Worth noting that many folding / feathering probs are *much* less efficient in reverse - they vary quite a bit, some are better than others. You did touch on maintenence, but for long distance cruisers the reduced risk of problems must be a tick for a simple bronze prop.
I really dig those Rigging Doctor educational (about propellers, keels, rigging etc) videos. Thanks for making them! After watching this video about propellers it makes me wonder, why don't sailboats have Controllable Pitch Propellers (CPP)? It would give you both port and starboard (by changing the pitch of the propeller) prop walk that you can abuse to get in or out of marinas...
Some sailboats do have them and it’s very nice. The problem is they are complicated and expensive. Also, if the consumer doesn’t know how to work it, the boat builder will have to deal with all the complaints about how the boat doesn’t motor well. I’ve been on a few boats that had different styles and I loved them all! One was a high or low pitch, one for marina maneuvering and the other for cruising and range. Another had fully adjustable pitch instead of a gearbox. The prop was always spinning, but the blades could be rotated to be straight for neutral or pointing forward or back for the direction. By adjusting the pitch, you could make the boat have more torque or more speed without touching the revs. That was by far my favorite! The captain set the revs for docking and did everything by throwing the pitch one way or another. His only complaint was that the prop can’t free wheel while sailing and the blades don’t feather all the way. Also, if he ran over a line, he had to shut the motor down as neutral still had the prop spinning. Everything always has to be a compromise!
Thanks for a great discussion of different prop types, why and when you'd want them, prop walk, etc. Really good stuff! The theory about water density causing prop walk seems very wrong. The difference in density from a few inches of depth in the water is insignificant. r m's discussion from naval architecture school sounds right. The hull is acting as an end plate to constrain the water movement and cause a side thrust.
While the various methods for explaining prop walk exist, I still do not know for certain which reason it is, or if it is wholly one reason and not a combination of reasons acting in synchrony. Our outboard motor has no cavitation plate and is a 13 inch propeller. When I have the motor trimmed perfectly, I get very little prop walk (which makes docking hard for me). I tilt the motor up a notch or two and suddenly I have plenty of prop walk to make docking easier for me (as it behaves more like our sailboat which has a level shaft in an aperture).
@@RiggingDoctor Another explanation is that the hull impedes the water at the top of the prop's path, which allows the water at the bottom of its path to move more freely. Agree it's a bit confusing.
You're suggesting that the 2-blade feathering Max-Prop would automatically set itself vertically when sailing. But that actually depends on the position of the shaft when turning the engine off. That will determine the angle of the propeller. If you absolutely want the blades to sit vertically, you'll have to check your shaft angle from the inside and potentially need to turn it, which is a pain..
@@RiggingDoctor It would ... Oooh you know just what to say !! The Darglow Featherstream has been in her mind.. Is there a way of writing to you other than here ? I only came upon your channel today and am very happy to tell you , an awful lot of sense is being spoken !!
Hi Doc. ........... enjoyed your video. Picked up a few bits of interesting info. Cost !!! NOT CHEAP. Another thing in my research on the net was the composite the blades are made from Zytel, a plastic composite made by DuPont is now used for the blades. High strength, abrasion, and impact resistant thermoplastic poly-amide formulations. Is this newer info or not from what you know? Cheers
My info is from other cruisers who had the blades polish down over the years. It was all word of mouth but from first hand experience on their part. I do not know what material or age their blades were, or if they still have the problem. I contacted Kiwi Prop to see if they would send me a prop to test out on our return voyage. I offered to weigh the blades before and after the crossing to find out conclusively what happens over thousands of miles of sailing but they were not interested in my proposal. Of all non-fixed propellers, Kiwi is my favorite design; it has simplicity which I find elegant. I just wish that I knew definitively if the blades polishing off is an issue or not.
In my thinking you forgot to mention with regards to the folding propellor is the complex reversing mechanism that they do have and which ups their costs as well. Otherwise, you made a good show of a fairly complicated subject, congratulations.
Prop walk occurs because the shaft of the propeller is usually at a downward angle toward the propeller. If the shaft was horizontal making the propeller perfectly vertical. You would not have prop walk.
In a single prop boat, yes you would still have some prop walk (think of it as a paddle wheel) but it wouldn’t be as noticeable. Most high powered twin engine boats have counter rotating props, even if the shafts are horizontal (saildrive & outboards)to cancel it out. I once owned a trawler with a massive four blade prop which was horizontally aligned with the keel, in an aperture, and it would only go one way in reverse.
This is my first time watching one of your videos. As I was watching this I thought you sounded familiar somehow. You have a similar cadence of speech to someone I 'know'. It came to me at the end- and it is someone that YOU know! Ryan, from Jessica and Ryan Adventures.
Guys, Kiwi props are not that cheap. They're about half the price of the others. There's just no way you can purchase a kiwi prop for $400. that just buys replacement blades!! I'm looking at them now and the 3 blade model is $1800 where a Max prop is close to $3k
You have to remember that a 3-blade fixed propeller is concave in the forward direction, and convex in the reverse, and therefore the thrust is a lot less at the same RPM in the backwards direction. This means that when the boat moves forward under sail, there is less drag, because the water is coming from behind the propeller. Furthermore, if the engine is put into neutral, then the propeller can spin under sail creating even less drag. However, my understanding is that spinning the propeller under sail is not good for the bearings (or something).
Some say it is bad for the transmission, but apparently it depends on the type of transmission that the boat has. We have an electric motor with direct drive so the spinning prop in neutral acts as a hydrogenerator to charge our batteries.
There are so many factors to decide on what the correct propeller should be. Engine HP and max RPM, gearbox ratios, size of boat, type of through hull prop shaft. I think a prop with an adjustable pitch is critically important for efficient and reliable engine function. Don't burn up your engine with too big a prop or an over pitched prop, it's important to be able to fine tune!
I’ve met a few cruisers with variable pitch props and it’s amazing! They set the RPM and then play with the pitch to set their speed. It gives them incredible range and efficiency while taking it easy on the motor.
Hiya - great vid and clarified a good few things for me so thanks for that....one thought. It's very easy to cast metal, could you not get a kiwi prop, take it apart and cast the parts in something stronger like bronze or aluminium, make a few spares up while your at it and then reassemble the prop with new metal parts?
I have thought about doing that, using the plastic bits as the mold too. The only hiccup is the blades are supposed to be buoyant so that they feather better, but that drag seems rather trivial compared to a fixed prop.
Great episode! It's nice to hear electric propulsion included in a talk about props. Regen is an other animal altogether. You mentioned propeller companies that are catering to EP, who are they?
interesting video. but you forgot what I was looking fore. Power in revers. I did use to have a fix blade. got a new boat with folding . It dos not work as I want it to in revers. so think about getting a fix for that reason. would love to know how all the different propeller handle revers quickly revers and forward :)
I can’t remember the brand, but there is a company that makes a propeller that works the same forward and reverse. The prop doesn’t look too fancy as the blades are plain and symmetrical. In a test comparing it to other fixed props, it had pretty low drag but it’s thrust in forward was the lowest of the bunch; but, it’s thrust in reverse was the highest of the lot and equivalent to its forward thrust. The main issue with it was that it would end up consuming more fuel to motor a long distance compared to the other props that are biased in their thrust. That said, low drag means that you can sail there and not use any fuel! I apologize for not remembering the name, or where I read about it. All I can remember is that it was in a magazine article where they compared a bunch of props which leads me to believe that it was Practical Sailor or Sail Magazine since they do tests like that. Good luck with your new prop! Reverse is the most important aspect in my opinion. When you want the boat to stop, you need it to stop in a hurry!
Have a saildrive w/ 3-blade. As stated, virtually no walk. Yanmar makes my drive and engine and over the years (I've had 3 models), they seem to go back and forth about keeping the boat in gear under way. The current guidelines (maybe more since they state you warranty is invalid if ignored) is to let it freewheel which I guess reduces some of the drag versus it being fixed? I suppose they are more concerned about the stress placed on the gears being in gear versus the engine parts moving without the oil pump and such operating as God intended?
To free wheel or not to free wheel, that is the question. Weather 'tis nobler to suffer the thrums and degredation or, by selecting, end them? Personally, I would arrive slower but without the noise.
Another great video. You covered everything that any regular sailor would need. You need to be a professional teacher when your done sailing. One of the best in the country is University of Alabama in Birmingham (not the main campus). My last Dentist before he retired, he spent 20 years teaching Dentistry. He was Awesome! Just saying.
very good video. I have a 2 part question of drag difference of a fixed two blade vs. fixed three blade? I have heard it's a full knot per hour difference in speed in terms of drag of a three vs. two blade on a sailboat 1)Wondering if that is accurate. 2) as an example of making a 50 mile run across to Bahamas from Miami and motoring on a Baba 30 sailboat - is the speed increased greatly on the three blade vs. two blade? Have always heard less time on the water when making a crossing the safer it would be....so am trying to weigh the two against one another. (gain in forward speed and the control when backing up in a marina vs. the additional drag when under sail, added cost or savings on fuel etc.... Not so concerned about a racing speed as the point is to be on the water sailing in the first place. More of overall benefit is what I am pondering, and wondering your thoughts as a more experienced sailor......
I have only had a 3 blade on Wisdom but Windpuff has a 2 blade that I would rotate (I marked the shaft so that I could tell where the blades were) so that they would be blind behind the keel. Windpuff sailed better than Wisdom in light air! This is however a very unfair comparison as Windpuff weighs 9,000 pounds and Wisdom 34,000 pounds. I don’t know if it is a full knot of lost speed, and you can get thinner blade props. Wisdom has massive blades that are a lot of drag but I’m certain a thinner blade would not be as horrendous. The issue with maneuvering a 2 blade over a 3 blade is the constant fluctuation in the number of functioning blades. On a 2 blade, the oscillation will be 2 - 0 - 2 - 0 and so on. This is because you will have 2 blades out to the sides of the keel then both blades behind the keel and blind to it, then the two blades come out again, then they hide, then they come out again. This results in a fluctuation in thrust and lost efficiency. When you are moving, you want a constant thrust but a 2 blade will give you thrust “most of the time”. A 3 blade however will always have 2 blades working as the top or bottom blade will go behind the keel but the other two will be out to the sides. The fluctuations of a 3 blade will be 2-3-2-3-2-3 and so on. This will give you a constant thrust when you are motoring which also makes them more efficient. Less time on a passage makes it safer, and electric let’s you set the prop to barely spin so that it isn’t giving thrust but it also isn’t causing drag, or you can turn off regen and let it free spin which is less drag than having it stopped. On Windpuff, the prop is too small of a diameter to produce power from regen, but I am still going to put a 3 blade on. I will be looking for a very thin fixed blade prop though as I don’t want the complexity of a feathering prop or the drag of a wide blade. I would suggest looking into the Sharrow props, they are a torus blade and offer very little drag with incredible performance. If they have finally come to market when I’m at that stage, that is the exact propeller I plan on using.
@@RiggingDoctor that makes sense about being behind the keel and the 2,0,2,0,2,0 etc.... Is there still benefit of using this 3 blade Sharrow on a diesel engine as I don't have plans to go electric as far as motor. Sounds like they have much less drag?
Nice simple explanation of props, good job. I've got a 3 blade fixed, fairly close to the rudder, hooked straight to a Yanmar 15 on my 28ft mid-eighties plastic tank. Pros? Simple as heck. Change the packing and anodes once in a while. Cons? Tons of walk and drag. A buddy of mine has a sort of similar boat with a sail drive and folding prop. Way better, really no comparison. That said, I'm not going to spend 6 to 10 grand to pick up half a knot. How about doing a video or three on boom rigging set-ups? I've noticed you went really minimalist and would like to know more about your choices.
There was a 24 foot boat for sale for about €1000 that had just sailed to the canaries, Azores, and now back to Portugal! But it had a very “interesting” setup.
Yes especially the high end ones with synchronised gear meshing blades like "Gori" and "Wisco" -- Gori can go over centre which reduces the diameter under load thus having a gearing like effect for better utilization of power under load.
I have a 2 blade fixed prop. I broke a blade and need to replace it. If I went to a 3 blade fixed. Can I use the same pitch, or need to go up or down. It is a 13" x 12 pitch right hand.
Sail drive (sometimes called S-drive) have an inconvenience : they aren’t protected! By this I mean that they can de severely damaged by an floating débris. It already happened several time, the entire protruding part was snapped off and this ended with a boat being flooded and as there wasn’t an large capacity pump on board’ the boat sunk! Why not build an protection, like on some rudders? You video is great !
That is exactly why we chose a boat with a full keel where the propeller is protected by t he rudder in an aperture. Horrible prop walk but great peace of mind!
Do you happen to know if kiwi props can help boat speed. I have a boat that doesn’t motor much, but is underpowered. Meaning on days with good 17-20 knot winds it’s a bit iffy on even taking her out. Due to the risks of her being overpowered by the wind when the sails aren’t up. Looking for not very expensive options for keeping this old YSM8 going but getting better performance out of her.
It’s going to be dependent on the pitch of the prop. If you decrease the pitch, you will increase your torque but cut your top speed. I’m not sure if the pitch is adjustable on Kiwi props. If it is, you are golden!
So, Saildrives with two blades and fixed propellers are the best for electric sailboats because they're reliable and cheap, and two blades have less drag than three or four blades, right?
The Max Prop Easy Prop is, by far, the best propeller solution for a sailboat. A folding prop requires waking up to make it efficient, while a feathering prop is at the ready for rotation and work. Prop walk is almost non-existent with this propeller. It is at least 40% more powerful than a folding prop in reverse. Folding props absolutely suck in reverse. Go for the Max Prop.
I jus installed an electric motor. I have a two plane fixed prop. We live on the west coast of Florida where crab traps abound in the billions. I’ve only been on two long sails on this boat and on both of them I picked up a crab trap. I guess I was used to my old full keel Morgan that didn’t suffer this problem. Regardless I would rather have a folding prop to slip past these crab trap lines. I read that a folding prop will give regen if you excite the prop. I’m shopping now to find out. The idea is to use regen by day when you can avoid the traps and feather at night when you can’t see them. I read that the best best prop would be about 15 x 15 three blade but you mentioned a lower pitch for regen? What do you have?
We have a 16 x 14 three blade. The keel does a good job of pushing crab pots out of the way but we have snagged a few in the Chesapeake Bay over the years (thankfully they always slip free).
1st: I’ve tried casting bronze and it is not as easy in practice as it is in theory. 2nd: I wonder if the plastic blades are needed for weight reasons where s bronze one might flop from weight. I imagine they would need to cast it hollow, not easy to do.
Thinking that boats/propellers travel straight ahead when sailing is wrong. No propeller hides perfectly behind any keel when sailing. Leeway causes the blades to see water coming at then from the side at all times when sailing. That is why folding propellers have less drag. Feathering propellers do not completely face water passing by perfectly. A little more drag than folding.
Prop regen only generates meaningful energy at minimum 6kn speeds maintained over many hours. At loer speeds the drag from the prop negates the regen. So prop regen makes sense on a 45ft cruising yacht out on passage 24/7
Agreed. When crossing an ocean, we enjoy it for the power it gives us. If we are coastal and making a short journey, we shut off the regen to avoid the speed penalty.
I need to buy a propeller for my displacement keel, aperatured, electrically powered boat. This video is EXCELLENT! I was leaning toward a three blade fixed for cost, but second guessing myself. Now, if I could just decide on the pitch... :) By the way, what kind of regen do you really see? I have the exact same motor as you.
Cool setup! What kind of powerboat? We want to get a trawler and make it electric when we get a little older :) At 5 knots, we get about 2amps, at 6-7 knots we see about 6 amps, and once at 8 knots we had 12 amps (all in 48v)
@@RiggingDoctor Sorry, it is not a powerboat, it's a sailboat... a Pearson 35. Max hull speed is about 6.5 knots. I'm in the Chesapeake with light winds in late summer, so regen won't be a huge factor. Thanks for the info, I was just curious what you experience.
It’s not great. They will always put wear on the driveline in some way. If you have an electric motor though, the spinning actually charges your batteries while you sail!
The fatal flaw of a sail drive is it hangs out there to get caught on anything. If it gets ripped off your boat your going to have a very big hole at deal with. Pretty much headed for the bottom.
While I wouldn’t want one on my boat for reasons you have mentioned, they do a great job of minimizing prop walk. Some things are more important that others and for some people, backing up straight is more important than safety 🤪
We are struggling about what to do with the two blade Max Prop on our , (new to us), 1989 Beneteau First 35s5. The prop is very pitted and suffering from lack of maintenance. PYI, Inc., the manufacturer, can refurbish the prop for about $1,000. When they install a Max Prop, they cut off about two inches and four or so threads off the end of the prop shaft. Will a fixed prop attach to our shortened shaft? Don't know until the prop shop sees the shaft. Then there is the other issue of the taper length of the shaft and the bushing issue of going from 25mm shaft to standard 1 1/8" bore of fixed props. The French didn't make it easy. We go back and forth on what to do.
Great video! You always have great information. Thank you! I am currently installing my motor from electric yacht now. Well actually building my battery box now🤗 so close so stoked to be on sailing with some regen with my fixed blade prop. Any advice on electric motors, wiring, how much you tax your batteries, how long you run your generator and what battery charger you use. We really appreciate your advice. ⛵✌
Awesome! I will get you detailed info shortly. Brief info is: 4 years on our first batteries, 0.5 years on our new batteries. Charger is Delta Q IC1200 I keep the regen set to “5” as this gives the least drag with regen still on. I also set the motor limiter to 30-50% when we are not in a marina so that we have more fine control of the throttle setting. In a marina, I raise the limiter to 70% of maximum power. In really tight places I take off the limiter so we can use all the power available.
@@RiggingDoctor wow! That's great to know. And makes great sense. Thank you. I'll keep you up to date we have a 1973 formosa ketch, she also has full keel. I think we will share similar results. Thank you for your time 🤙
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Prop walk: the blade at the top of its turn, ie 12 o'clock, gets a bit of end plate effect so gives a bit more side thrust as it passes through 12 o'clock (tip vortex is reduced at 12 o'clock). That's why you get the imbalance of side thrust. At least that's what I was taught getting my bachelors in nav. arch. Prop walk can vary depending on the flow into the prop also, which is affected by speed and hull shape. Prop walk is really noticeable on tugboats that have old style fixed props on a shaft.
Number of blades... usually you want to keep the blade number not an even fraction of the engine cylinders to keep vibration down (can be exceptions). I.e. if your engine has 4 cylinders, having 3 blades is better than 2 or 4 blades. This is due to the additional side thrust of the 12 o'clock blade. If you have an even multiple of blades to cylinders, you tend to get a sync of a cylinder firing at the same time you get that extra side force on the shaft, which can cause a vibration.
Good vid, brings back memories of my segment in school on prop design.
interesting addition on the blade count - thanks!
generic comment.... I never heard of your explanations.
Did you smoke a lot of funny tobacco when you were in college?
Comment is correct. Sail drives CAN have prop walk. Depending on the layout, they can have a lot of prop walk.
@Mission Gameliel Not when crossing oceans or night sailing or if you don't have enough room for the amount of panels needed for the amount of power required.
Solar is good and very good, but it's not a solve all resource.
If solar alone could do as you say then why solar is not fitting for all solar powered boats? More so the small day boats! (SOLAR HAS IT'S PLACE BUT IT'S NOT A SOLVE ALL)
Interesting your opinion on Kiwi Props.
My experience, and the advice of the creator /manufacturer is lube on annual haul out!
I've found that to be effective.
I've not seen any erosion of the plastic blades, probably due to application of Prop Speed, so other than lube and prop speed I've had no maintenance issues in 6 years.
For a professional skipper who specialized in 12-day trips France to Ireland and back (64 trips total), a folding propeller him gave a good half-day gain on the whole trip. That meant one more stopover in a beautiful anchorage. Speed prediction formulas used in handicap systems assume a mix and upwind and downwind. A folding/feathering prop can make a 1.5-knot difference going upwind, easily. If the conditions are rough (against the current), that could even mean making it to destination vs. not.
The episode conveying the most 'wisdom' of all of your videos, imo. Very nice job, Herbie. Thank you for making that whole complicated issue/topic much clearer for me, and I'm guessing many others as well. Carry on, sailor.
Thanks! Great job. Third time I watched it. I’m going to emphasize P-factor. Airplane propellors get that in a high pitch. Boats with downward angled shafts get it even more. Propwalk will be most pronounced moving forward at low speed and high power and less so in reverse at low speed and low power. It just seems that it’s worse in reverse because of the pucker factor going into a slip and confusion over which way to turn the wheel. You guys are fantastic. Congratulations on your baby. And looking forward to more videos soon when you’re ready.
Thank you so much!
I was wondering about the P-factor but you explained it perfectly later in the comment.
Super information and delivery. A natural teacher. It's very clear that you researched the subject in great depth and left no stone upturned. Everything was covered in a very considered and systematic manner. Each question that came to my mind was subsequently answered. Your technical knowledge is second to none and your channel is an excellent resource for all things sailing related. Thanks for taking the time to make the video and share the knowledge.
I just want to point out that a kiwi prop costs us$1500 for a 3 blades and OR $150 each blade when you change them.
So I think the doctor just looked at the prices for extra blades ☺️
This was so much of what I was searching for. Thorough and well organised explanation. I learnt a lot watching this.
You are very welcome
we have a 2 blade maxprop. Working on getting it rebuilt after using it problem free for 16 years. After taking it apart we found some damage inside, but it still worked without issue. Highly recommended, there is a trick to get it to feather, but you can tell when it is not feathered because the shaft spins and you can hear that on our boat. A quick pop into reverse and then neutral when the engine is off feathers the prop and the shaft stops spinning.
My boat came with an Atomic-4 engine with a folding prop (forget the brand). I liked the prop. I had no problems with it, and, though people said the prop walk would be worse, I had very little prop walk. Maintenance was about the same as a fixed prop. I converted to electric, and stayed with the folding prop for the first year. It was fine.
After that, I got a used fixed prop at a very good price and wanted to test regen, so I changed the prop out. I noticed no appreciable change in sailing, and I can get a little (very little) regen when I sail >5 knots.
Once again, you have proven why you guys have one of the best channels on YT. Excellent presentation and information...
Thank you very much!
You've outdone yourself once again Herbie. EXCELLENT JOB and well wort the watch. PEACE OUT! Ü
Great presentation! I don't know what date it was recorded but it may require updated especially regarding Kiwiprop pricing and blade composite which are (now) made using Dupont's Zylan HTN composite.
Thanks for the great video! We were on the fence about buying a folding propellor (we have a fixed prop). Got to the end of the video and your information about time saved was invaluable! We had estimated more lost time from dragging. We are going to stick with our fixed prop for now. Thanks again!
Glad it helped! Keep your life simple so you can focus on other parts of the boat 😎
Herbie, HERBIE, hERBIE, I love ya man but u gotta get over this molecular plastic prop phobia. The first time i heard you say that (on a different video) i stopped in my tracts and backed up the video to be sure I heard you correctly. Later I found out you are a dentist which makes your comment seem so strange. As an engineer i can assure you your dental practice and day to day living not to mention the sunglasses on your head - contributes far more environmental pollution than plastic prop's microscopic ware in the frigging ocean. Sorry just couldn,t take it a 2nd time LOL. What makes me truly sad is we keep dumping trash in the ocean and it shows up on the shorelines of even the most remote islands. Love you and your sweet wife( and the birds) and have learned soo much about sailing from u 2. Keep up the good work!! PS Please listen to your wife about boat design especially on the artistic aspects of modifying a lady boat's rear end!!.😍
Haha! It’s all good. Every bit counts, and there is a lot going out there!! Thankfully they are starting to clean up the massive amounts of fishing equipment that is floating out there to help the oceans.
I do love these props and think they are the best design of feathering/folding props!
Thank you for this great presentation, we are seriously considering changing our 2 blade fixed for either a flexofold or featherstream . Your explanation of prop walk is clear and easy to understand.
So glad we could help!
Great video! You've helped me decide.
I have a two blade J Prop on our C34 MkII. It has a slight prop walk to port but feathers beautifully. I love your splicing videos. Really having problems finishing the knots on soft shackles though!
I used to be a merchant mariner, and was taught that our prop walk was a result of the pressure differential between the blades. We were talking 18 foot diameter props !
🫨 18 foot!! Sailboat props must look like a handheld personal fan!
Are you doing a button knot or the lovers knot? I like the lovers knot for a few reasons, but you can splice the tails of the knot into each other to make a single tail that is really handy for guiding the knot through the loop.
Great video Herbie. Again, your depth of knowledge and ability to convey it, is impressive. Prop walk is a pain... I owned a diesel powered Pearson with an offset propeller shaft to counter prop walk. Backing out of a slip with that offset shaft can be a major PITA depending on which way you needed to travel out of the slip and how much room you have backing out. If you back out with low speed, she walks. Some spots were tight enough a hi speed burst may not be advisable. Then of course, add the effect of currents! Like you, I paid real close attention to where and how I tied up. ;-) Well done video. Great explanation!
I have s two bladed folding prop on a standard propshaft. I get prop walk to starboard in reverse. I use this to advantage when coming into my slip because I can come almost abreast of my slip give full rudder to port and a stab of reverse and she'll pivot about her keel and I can then motor straight in. Simples!
Great explanation... I get it now... great video
Bronze Kiwi propeller is a really great idea!
Great job Herbie!
I had a 2 blade ELICHE RADICE prop while sailing in the great lakes as part of preparing to head on down the erie canal then the icw and crossing oceans I decided to replace it with a 3 blade folding flex-o-fold. I ended up with the same speed but more torq. prop walk just a little less, under power. under sail I saw no difference. The big advantage I gained was coming into a dock was stopping distance, I would guess 1/4 boat length quicker. A fixed 14" prop under sail is like dragging a 5 gallon bucket behind the boat! But where you want the prop shaft to spin makes total sense. Bob
.......and then there is also the "variable pitch" propeller, usually controlled via hydraulics. It allows for very fine, infinite control, however it's a fairly complex system that is very expensive. Not usually found on the average yacht, but on the larger mega-yachts owned by billionaires (both sail and power). By the way Herby: You did an excellent job with your propeller lecture. You pretty much covered all the bases and offered a few compelling arguments for and against various types of props and their design characteristics. It appears you've done your homework. In fact you were so convincing, I'm thinking about getting rid of the prop and switching to oars (totally eliminates prop walk😁).
Hunsted makes a really good vari-pitch prop.
The dominant vs weak arm comes into play once you go with the human propulsion, though. ;)
@@SkySailor75 🤣🤣
When I was in highschool in Puerto Rico, we referred to it as the “sinning arm”
@@RiggingDoctor LOL
Love this episode. It wasn’t the info I was searching for but learned/ crystallized prior learning so well. Thank you for doing what you do!
Thanks :)
Nice interesting piece which covers it all. One point I'd like to add is I would serious miss my prop if it were not nice and close to the rudder blade. Manoeuvring does require experience as to which way the boat will turn when you put it in astern from standing still. BUT with the rudder close to the prop the walk is really small in ahead as you can blast water direct on to the rudder and make the boat turn any way you want almost immediately.
I know what you mean, it’s practically a stern thruster! I tried to dock a boat that the prop was far from the rudder and it was a very ungrateful event.
I own a Max-Prop and am very happy with it. In terms of maintenance, It requires grease every time I replace the anode.
Prop walk is caused by the difference in water level on each side of the boat. We know that a right hand propeller walks the boat to port in reverse. In reverse, the top blade pushes water against the hull and the limited space rises the water level on the starboard side. The bottom blade has plenty of space to move the water hence lowers the water level on the port side. The difference in water levels pushes the boat sideways to port.
The Max-Prop is 84% efficient in both directions. It is more efficient than a fixed blade in reverse. The Max-Prop won't stop rotating unless you stop the shaft from turning using the reverse gear. While it is turning, it can be used for the generator. When you are tired of the noise it creates inside the boat, you simply stop it. Cheers, Richard
They really are an awesome design!
The most efficient prop is one with the fewest blades (though one is not that practical), as big as possible, so it will have a smaller pitch to suit. Sailboat props are all about static thrust, think trying to make headway against a very strong wind.
On the sailing ship I was on we had twin Eight cylinders Gardners engines with variable pitch and folding propellers.
Nice
Richard Mason , yes it was very nice
I have had my yacht for 11 years, it came with a kiwi prop and it still has the same prop. I Antifoul the prop so maybe that is why my prop hasn’t desolved as you suggest. Works for me
That’s great to hear!
Kiwi props are actually my favorite “non fixed” prop. They are the simplest design and have the fewest points of failure.
Brilliant video, good timing also as was just considering changing my fixed 3 blade, have to say might not bother now
The 2-blade Max-Prop model that you showed is supposedly capable of re-gen if you reverse just before turning off the engine. I don't have the capability to re-gen, but I know how to make the shaft turn if I want (provided I sail fast enough). Answering to one of your points about fixed blade propellers being always more efficient, I have to say the feathering mechanics ensure that the leading edge of the blade remains a leading edge when reversing. The featuring Max-Prop has amazing reverse performance.
Very informative! Thank you!
I have a feathering 3 blade PYI style, love it. did not want the noise of the spinning fixed prop, did not want to deal with a shaft brake.
Nothing wrong with prop walk, just have to know how and when to use it
This informative, instructive video, is the reason why I subscribed!
Hello nice video looking for the next I learned many more things about propellers. Saludos
Thank you very much. Comprehensive coverage on the subject and I learned something new to me which is Kiwi prop. But I must admit that by the 12:00 minute mark my head is spinning like a propeller trying to catch the torrent of terms rolling off your commentary. So I did what was best for me - listen, rewind, listen, stop and think, and head forward to the next segment. That's me, of course. Your knowledge is awesome.
Glad it was helpful :)
Interesting opinion on Kiwi Props.
My experience, and the advice of the creator /manufacturer is lube on annual haul out is essential!
I've found that to be effective.
I've not seen any erosion of the plastic blades, probably due to application of Prop Speed, so other than lube and prop speed I've had no maintenance issues in 6 years.
What an interesting discussion, about the opposite prop walk when drifting forward compared to when the boat is still. I can't say I have practically seen that, maybe because I am usually drifting very slowly when entering a slip. Reading the comments, it seems to be another illustration of the Dunning Kruger effect, overconfidence by those with less experience. Many of us sail on just a few boats regularly over a lifetime. In the end, learn how your boat responds and use that to advantage.
So informative, thanks Herby. Give Maddie a hug for us, please.
😊
Great talk and real life examples! Couple of thoughts , the extra drag from the extra blades requires more hp because of the extra drag from the same dia blade, gets complicated obviously but Tugs with unlimited power have 5-6-7 blades.
Prop walk in forward is compensated on a properly designed single engine yacht by having the prop shaft at a slight angle to center line 1-2 deg is typical. Love you point about port propwash in FWD and stb in reverse !
Some interesting looking yachts in that yard too!
Cheers Warren
I have a U-8D that has twin props. It is actually an airplane, so they have prop walk of sorts as well. Some planes have counter rotating props and some don't. Mine does not. In fact if you lose a particular engine the torque effect may become more than the plane can handle and you get crash city. Though both props can be feathered with a control lever. With a boat I was always taught to put your rudder in the opposite direction of prop walk. That way if you can exactly control the boats speed and the prop speed you can get steerage in both directions at a relatively low relative boat speed.
I believe (hypothesize) that the reason prop walk works "backwards" when you have forward way on is that the wash is not acting on the keel but on the rudder until the boat is stopped, then it starts working on the keel. Just a thought from a guy with a full keel boat that (in reverse) walks to port like crazy!
Amazing channel. Best on You Tube.
Great explantion of prop-walk!
Thanks
prop-talk.
Very Informative video. Thanks. I learned something today.
I came across your video. Very informative, thanks for making it! One thing i do miss, or better I thought of seeing your video is the relation of drag/ loss of speed to the boat LWL and hullshape, cat or tri etc. For a small monohull a fixed large prop can make a difference of 0.5 to 1 knot. meaning 0.5 to 1 Nm per hour less distance. which is significant enough to change a setup. For a bigger vessel this number is reduced 0.1 to 0.2 knots or Nm/h. As for Propwalk...Single engine aircrafts experience this too, specially dragging tail aircrafts at low speed. (Prop is on an angle) Propwash is cause that the effect going forward is different than goin in reverse.
This would seem to be a logical lead-in to a video on the pros and cons of saildrives.
Good idea!
Great video. Thanks for posting
Thank you SO much on the i sights regarding props... much appreciated! Will have to look into your system re electric motor.
Good info here. I will send people here instead of trying to explain it and have people looking at me like I’m speaking another language lol. 👍
Thanks! I appreciate it :)
Great to see a few bilge keels in the background🤙
They were a pretty common sight in Portuguese boat yards. Very cool designs!
@@RiggingDoctor love my bilgey
Great presentation & excellent video
Thanks!
Don't have a boat ....yet, but trying to learn lots before I do. Great information 👌
If you have any questions, let us know and we can make a video on the topic or point you in the right direction for that information.
@@RiggingDoctor well thanks! Appreciate that! Wind and/or wind direction, weather, and sails is still a huge topic I've been trying to learn about. So many differences of opinion!
Regarding the kiwi prop, there are a couple of comments that I find difficult to take seriously. Life span, what is short or long? I drove a kiwi on a Harmony 34 between 2007 and 2018. No problems to report from that period. It is probably more important to make sure that these propellers are well lubricated and that the seals that hold the grease in place are changed at appropriate intervals. Wear of material in the blades? I haven't seen any of that at all, the last few years a layer of antifouling was put on the blades, it disappears with time but not so fast either. I see no reason why it wouldn't have worked for another ten years. And a big advantage, the blades angles can be adjusted to have the engine run on desired revs.
Good to know! I have friends in the Chesapeake Bay who have had to replace blades every 5 years or so. Makes me wonder what is in the Chesapeake!
One friend barely moved his boat and the sun always hit one blade in particular. One blade disintegrated and it is assumed to have been the one that always had the sun hitting it while in the slip.
Another friend (who first introduced me to kiwi props) told me about the polishing blades. He works at a boat yard in Baltimore and frequently would have to replace worn down blades on kiwi props.
I really love them! Their simplicity, reliability, and adjustability make them the best non-fixed propeller in my opinion. I’m glad to know you didn’t have the blade polishing issue :) it might just be an issue in the bay.
Herb...One of your better ones..GREAT JOB!!
Thanks 😊
Great vid as usual. Worth noting that many folding / feathering probs are *much* less efficient in reverse - they vary quite a bit, some are better than others. You did touch on maintenence, but for long distance cruisers the reduced risk of problems must be a tick for a simple bronze prop.
That’s why we really like our fixed propeller. If it is present, it works ⛵️
I really dig those Rigging Doctor educational (about propellers, keels, rigging etc) videos. Thanks for making them! After watching this video about propellers it makes me wonder, why don't sailboats have Controllable Pitch Propellers (CPP)? It would give you both port and starboard (by changing the pitch of the propeller) prop walk that you can abuse to get in or out of marinas...
Some sailboats do have them and it’s very nice. The problem is they are complicated and expensive. Also, if the consumer doesn’t know how to work it, the boat builder will have to deal with all the complaints about how the boat doesn’t motor well.
I’ve been on a few boats that had different styles and I loved them all!
One was a high or low pitch, one for marina maneuvering and the other for cruising and range. Another had fully adjustable pitch instead of a gearbox. The prop was always spinning, but the blades could be rotated to be straight for neutral or pointing forward or back for the direction. By adjusting the pitch, you could make the boat have more torque or more speed without touching the revs.
That was by far my favorite! The captain set the revs for docking and did everything by throwing the pitch one way or another.
His only complaint was that the prop can’t free wheel while sailing and the blades don’t feather all the way. Also, if he ran over a line, he had to shut the motor down as neutral still had the prop spinning. Everything always has to be a compromise!
Thanks for a great discussion of different prop types, why and when you'd want them, prop walk, etc. Really good stuff!
The theory about water density causing prop walk seems very wrong. The difference in density from a few inches of depth in the water is insignificant.
r m's discussion from naval architecture school sounds right. The hull is acting as an end plate to constrain the water movement and cause a side thrust.
While the various methods for explaining prop walk exist, I still do not know for certain which reason it is, or if it is wholly one reason and not a combination of reasons acting in synchrony.
Our outboard motor has no cavitation plate and is a 13 inch propeller. When I have the motor trimmed perfectly, I get very little prop walk (which makes docking hard for me). I tilt the motor up a notch or two and suddenly I have plenty of prop walk to make docking easier for me (as it behaves more like our sailboat which has a level shaft in an aperture).
@@RiggingDoctor Another explanation is that the hull impedes the water at the top of the prop's path, which allows the water at the bottom of its path to move more freely.
Agree it's a bit confusing.
You're suggesting that the 2-blade feathering Max-Prop would automatically set itself vertically when sailing. But that actually depends on the position of the shaft when turning the engine off. That will determine the angle of the propeller. If you absolutely want the blades to sit vertically, you'll have to check your shaft angle from the inside and potentially need to turn it, which is a pain..
Excellent and very interesting .. Just saved myself 1800£ +, Thank you !!
You are very welcome. Would the possible prop be for that gorgeous gaff rig in your picture?
@@RiggingDoctor It would ...
Oooh you know just what to say !!
The Darglow Featherstream has been in her mind..
Is there a way of writing to you other than here ?
I only came upon your channel today and am very happy to tell you , an awful lot of sense is being spoken !!
@@Trevessa24what did you decide on? We are currently considering the 3 blade Featherstream .
Message me on my channel Bev.
@@Trevessa24 seem to be unable to comment in your channel?
Hi Doc. ........... enjoyed your video. Picked up a few bits of interesting info. Cost !!! NOT CHEAP. Another thing in my research on the net was the composite the blades are made from Zytel, a plastic composite made by DuPont is now used for the blades. High strength, abrasion, and impact resistant thermoplastic poly-amide formulations.
Is this newer info or not from what you know?
Cheers
My info is from other cruisers who had the blades polish down over the years. It was all word of mouth but from first hand experience on their part. I do not know what material or age their blades were, or if they still have the problem.
I contacted Kiwi Prop to see if they would send me a prop to test out on our return voyage. I offered to weigh the blades before and after the crossing to find out conclusively what happens over thousands of miles of sailing but they were not interested in my proposal.
Of all non-fixed propellers, Kiwi is my favorite design; it has simplicity which I find elegant. I just wish that I knew definitively if the blades polishing off is an issue or not.
thanks, that is a great explanation...of something the +average sailor probably thinks they have a handle on...like me
Gave u a great review 2 months ago. But love seeing it again!
My retention is getting slower....lol! 🤣
Thanks :)
In my thinking you forgot to mention with regards to the folding propellor is the complex reversing mechanism that they do have and which ups their costs as well. Otherwise, you made a good show of a fairly complicated subject, congratulations.
Thanks 😊
Very interesting thanks .
Very welcome
Prop walk occurs because the shaft of the propeller is usually at a downward angle toward the propeller. If the shaft was horizontal making the propeller perfectly vertical. You would not have prop walk.
In a single prop boat, yes you would still have some prop walk (think of it as a paddle wheel) but it wouldn’t be as noticeable. Most high powered twin engine boats have counter rotating props, even if the shafts are horizontal (saildrive & outboards)to cancel it out.
I once owned a trawler with a massive four blade prop which was horizontally aligned with the keel, in an aperture, and it would only go one way in reverse.
This is my first time watching one of your videos. As I was watching this I thought you sounded familiar somehow. You have a similar cadence of speech to someone I 'know'. It came to me at the end- and it is someone that YOU know! Ryan, from Jessica and Ryan Adventures.
I see you took up my Suggestion. Great.
Guys, Kiwi props are not that cheap. They're about half the price of the others. There's just no way you can purchase a kiwi prop for $400. that just buys replacement blades!! I'm looking at them now and the 3 blade model is $1800 where a Max prop is close to $3k
You have to remember that a 3-blade fixed propeller is concave in the forward direction, and convex in the reverse, and therefore the thrust is a lot less at the same RPM in the backwards direction. This means that when the boat moves forward under sail, there is less drag, because the water is coming from behind the propeller. Furthermore, if the engine is put into neutral, then the propeller can spin under sail creating even less drag. However, my understanding is that spinning the propeller under sail is not good for the bearings (or something).
Some say it is bad for the transmission, but apparently it depends on the type of transmission that the boat has.
We have an electric motor with direct drive so the spinning prop in neutral acts as a hydrogenerator to charge our batteries.
@@RiggingDoctor Right, but I meant for diesel engines.
There are so many factors to decide on what the correct propeller should be. Engine HP and max RPM, gearbox ratios, size of boat, type of through hull prop shaft. I think a prop with an adjustable pitch is critically important for efficient and reliable engine function. Don't burn up your engine with too big a prop or an over pitched prop, it's important to be able to fine tune!
I’ve met a few cruisers with variable pitch props and it’s amazing! They set the RPM and then play with the pitch to set their speed. It gives them incredible range and efficiency while taking it easy on the motor.
Hiya - great vid and clarified a good few things for me so thanks for that....one thought. It's very easy to cast metal, could you not get a kiwi prop, take it apart and cast the parts in something stronger like bronze or aluminium, make a few spares up while your at it and then reassemble the prop with new metal parts?
I have thought about doing that, using the plastic bits as the mold too. The only hiccup is the blades are supposed to be buoyant so that they feather better, but that drag seems rather trivial compared to a fixed prop.
Great episode! It's nice to hear electric propulsion included in a talk about props. Regen is an other animal altogether. You mentioned propeller companies that are catering to EP, who are they?
interesting video. but you forgot what I was looking fore. Power in revers. I did use to have a fix blade. got a new boat with folding . It dos not work as I want it to in revers. so think about getting a fix for that reason. would love to know how all the different propeller handle revers quickly revers and forward :)
I can’t remember the brand, but there is a company that makes a propeller that works the same forward and reverse. The prop doesn’t look too fancy as the blades are plain and symmetrical. In a test comparing it to other fixed props, it had pretty low drag but it’s thrust in forward was the lowest of the bunch; but, it’s thrust in reverse was the highest of the lot and equivalent to its forward thrust.
The main issue with it was that it would end up consuming more fuel to motor a long distance compared to the other props that are biased in their thrust. That said, low drag means that you can sail there and not use any fuel!
I apologize for not remembering the name, or where I read about it. All I can remember is that it was in a magazine article where they compared a bunch of props which leads me to believe that it was Practical Sailor or Sail Magazine since they do tests like that.
Good luck with your new prop! Reverse is the most important aspect in my opinion. When you want the boat to stop, you need it to stop in a hurry!
@@RiggingDoctor Thanks for a long answer :) I will look myself if I find some who mention that problem
Herb... Very interesting. You could show us how to turn a boat in its own length using prop walk....it would make a nice vid,
In fact I challenge you!!
Have a saildrive w/ 3-blade. As stated, virtually no walk. Yanmar makes my drive and engine and over the years (I've had 3 models), they seem to go back and forth about keeping the boat in gear under way. The current guidelines (maybe more since they state you warranty is invalid if ignored) is to let it freewheel which I guess reduces some of the drag versus it being fixed? I suppose they are more concerned about the stress placed on the gears being in gear versus the engine parts moving without the oil pump and such operating as God intended?
To free wheel or not to free wheel, that is the question. Weather 'tis nobler to suffer the thrums and degredation or, by selecting, end them? Personally, I would arrive slower but without the noise.
Another great video. You covered everything that any regular sailor would need. You need to be a professional teacher when your done sailing. One of the best in the country is University of Alabama in Birmingham (not the main campus). My last Dentist before he retired, he spent 20 years teaching Dentistry. He was Awesome! Just saying.
When we get back, I do plan on teaching on the side. Part time faculty at the dental school and give talks at sailing classes.
@@RiggingDoctor you should! You will be fantastic! And all you have to do for your resume is show them these videos! Resume, check, check!
very good video. I have a 2 part question of drag difference of a fixed two blade vs. fixed three blade? I have heard it's a full knot per hour difference in speed in terms of drag of a three vs. two blade on a sailboat 1)Wondering if that is accurate. 2) as an example of making a 50 mile run across to Bahamas from Miami and motoring on a Baba 30 sailboat - is the speed increased greatly on the three blade vs. two blade? Have always heard less time on the water when making a crossing the safer it would be....so am trying to weigh the two against one another. (gain in forward speed and the control when backing up in a marina vs. the additional drag when under sail, added cost or savings on fuel etc.... Not so concerned about a racing speed as the point is to be on the water sailing in the first place. More of overall benefit is what I am pondering, and wondering your thoughts as a more experienced sailor......
I have only had a 3 blade on Wisdom but Windpuff has a 2 blade that I would rotate (I marked the shaft so that I could tell where the blades were) so that they would be blind behind the keel. Windpuff sailed better than Wisdom in light air!
This is however a very unfair comparison as Windpuff weighs 9,000 pounds and Wisdom 34,000 pounds.
I don’t know if it is a full knot of lost speed, and you can get thinner blade props. Wisdom has massive blades that are a lot of drag but I’m certain a thinner blade would not be as horrendous.
The issue with maneuvering a 2 blade over a 3 blade is the constant fluctuation in the number of functioning blades.
On a 2 blade, the oscillation will be 2 - 0 - 2 - 0 and so on. This is because you will have 2 blades out to the sides of the keel then both blades behind the keel and blind to it, then the two blades come out again, then they hide, then they come out again. This results in a fluctuation in thrust and lost efficiency. When you are moving, you want a constant thrust but a 2 blade will give you thrust “most of the time”.
A 3 blade however will always have 2 blades working as the top or bottom blade will go behind the keel but the other two will be out to the sides. The fluctuations of a 3 blade will be 2-3-2-3-2-3 and so on. This will give you a constant thrust when you are motoring which also makes them more efficient.
Less time on a passage makes it safer, and electric let’s you set the prop to barely spin so that it isn’t giving thrust but it also isn’t causing drag, or you can turn off regen and let it free spin which is less drag than having it stopped.
On Windpuff, the prop is too small of a diameter to produce power from regen, but I am still going to put a 3 blade on. I will be looking for a very thin fixed blade prop though as I don’t want the complexity of a feathering prop or the drag of a wide blade.
I would suggest looking into the Sharrow props, they are a torus blade and offer very little drag with incredible performance. If they have finally come to market when I’m at that stage, that is the exact propeller I plan on using.
@@RiggingDoctor that makes sense about being behind the keel and the 2,0,2,0,2,0 etc.... Is there still benefit of using this 3 blade Sharrow on a diesel engine as I don't have plans to go electric as far as motor. Sounds like they have much less drag?
Nice simple explanation of props, good job. I've got a 3 blade fixed, fairly close to the rudder, hooked straight to a Yanmar 15 on my 28ft mid-eighties plastic tank. Pros? Simple as heck. Change the packing and anodes once in a while. Cons? Tons of walk and drag.
A buddy of mine has a sort of similar boat with a sail drive and folding prop. Way better, really no comparison. That said, I'm not going to spend 6 to 10 grand to pick up half a knot.
How about doing a video or three on boom rigging set-ups? I've noticed you went really minimalist and would like to know more about your choices.
Good idea! They will be coming out soon ;)
thanks for the info. if you're still there maybe you could do a tour of the yard and any boats for sail or abandand.
Thanks! We are actually in Spain now
There was a 24 foot boat for sale for about €1000 that had just sailed to the canaries, Azores, and now back to Portugal! But it had a very “interesting” setup.
Now we know...
Can feather propellers go in reverse? Very informative video by the way.
They can, and you can lock them in reverse for regen mode with electric motors
Yes especially the high end ones with synchronised gear meshing blades like "Gori" and "Wisco" -- Gori can go over centre which reduces the diameter under load thus having a gearing like effect for better utilization of power under load.
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@@RiggingDoctor How is that done? Is it the same for all kinds of folding/feathering propellers?
I have a 2 blade fixed prop. I broke a blade and need to replace it.
If I went to a 3 blade fixed. Can I use the same pitch, or need to go up or down. It is a 13" x 12 pitch right hand.
Sail drive (sometimes called S-drive) have an inconvenience : they aren’t protected! By this I mean that they can de severely damaged by an floating débris. It already happened several time, the entire protruding part was snapped off and this ended with a boat being flooded and as there wasn’t an large capacity pump on board’ the boat sunk!
Why not build an protection, like on some rudders?
You video is great !
That is exactly why we chose a boat with a full keel where the propeller is protected by t he rudder in an aperture.
Horrible prop walk but great peace of mind!
Do you happen to know if kiwi props can help boat speed. I have a boat that doesn’t motor much, but is underpowered. Meaning on days with good 17-20 knot winds it’s a bit iffy on even taking her out. Due to the risks of her being overpowered by the wind when the sails aren’t up.
Looking for not very expensive options for keeping this old YSM8 going but getting better performance out of her.
It’s going to be dependent on the pitch of the prop. If you decrease the pitch, you will increase your torque but cut your top speed. I’m not sure if the pitch is adjustable on Kiwi props. If it is, you are golden!
Will a 2 bladed prop position itself vertically behind the rudder or do you have to rotate it into position?
So, Saildrives with two blades and fixed propellers are the best for electric sailboats because they're reliable and cheap, and two blades have less drag than three or four blades, right?
Pretty much, but you won’t get Regen with a 2 blade, so you need to weigh out your options.
The Max Prop Easy Prop is, by far, the best propeller solution for a sailboat. A folding prop requires waking up to make it efficient, while a feathering prop is at the ready for rotation and work. Prop walk is almost non-existent with this propeller. It is at least 40% more powerful than a folding prop in reverse. Folding props absolutely suck in reverse. Go for the Max Prop.
I jus installed an electric motor. I have a two plane fixed prop. We live on the west coast of Florida where crab traps abound in the billions. I’ve only been on two long sails on this boat and on both of them I picked up a crab trap. I guess I was used to my old full keel Morgan that didn’t suffer this problem. Regardless I would rather have a folding prop to slip past these crab trap lines. I read that a folding prop will give regen if you excite the prop. I’m shopping now to find out. The idea is to use regen by day when you can avoid the traps and feather at night when you can’t see them. I read that the best best prop would be about 15 x 15 three blade but you mentioned a lower pitch for regen? What do you have?
We have a 16 x 14 three blade. The keel does a good job of pushing crab pots out of the way but we have snagged a few in the Chesapeake Bay over the years (thankfully they always slip free).
Could you get a kiwi prop, take it apart and use the pieces to cast a bronze one?
1st: I’ve tried casting bronze and it is not as easy in practice as it is in theory.
2nd: I wonder if the plastic blades are needed for weight reasons where s bronze one might flop from weight.
I imagine they would need to cast it hollow, not easy to do.
Thinking that boats/propellers travel straight ahead when sailing is wrong. No propeller hides perfectly behind any keel when sailing. Leeway causes the blades to see water coming at then from the side at all times when sailing. That is why folding propellers have less drag. Feathering propellers do not completely face water passing by perfectly. A little more drag than folding.
Also shaft angle will make a feathering prop be more in the way than a folding prop.
Perhaps a bit of overspeak, but certainly interesting stuff.
Prop regen only generates meaningful energy at minimum 6kn speeds maintained over many hours. At loer speeds the drag from the prop negates the regen. So prop regen makes sense on a 45ft cruising yacht out on passage 24/7
Agreed. When crossing an ocean, we enjoy it for the power it gives us. If we are coastal and making a short journey, we shut off the regen to avoid the speed penalty.
I need to buy a propeller for my displacement keel, aperatured, electrically powered boat. This video is EXCELLENT! I was leaning toward a three blade fixed for cost, but second guessing myself. Now, if I could just decide on the pitch... :)
By the way, what kind of regen do you really see? I have the exact same motor as you.
Cool setup! What kind of powerboat? We want to get a trawler and make it electric when we get a little older :)
At 5 knots, we get about 2amps, at 6-7 knots we see about 6 amps, and once at 8 knots we had 12 amps (all in 48v)
@@RiggingDoctor Sorry, it is not a powerboat, it's a sailboat... a Pearson 35. Max hull speed is about 6.5 knots. I'm in the Chesapeake with light winds in late summer, so regen won't be a huge factor. Thanks for the info, I was just curious what you experience.
I assume that folding props are not s likely to catch on floating lines (when folded), whilst feathering props still have this issue.
I assume that as well, but if you are unlucky, it could be both snagged or pinched in the blades
What about gearbox wear when fixed props are spinning. Of Even when they are in gear and gearbox is fully loaded in reverse?
It’s not great. They will always put wear on the driveline in some way. If you have an electric motor though, the spinning actually charges your batteries while you sail!
Out of curiosity, do cats have opposite turning props?
The fatal flaw of a sail drive is it hangs out there to get caught on anything. If it gets ripped off your boat your going to have a very big hole at deal with. Pretty much headed for the bottom.
While I wouldn’t want one on my boat for reasons you have mentioned, they do a great job of minimizing prop walk.
Some things are more important that others and for some people, backing up straight is more important than safety 🤪
We are struggling about what to do with the two blade Max Prop on our , (new to us), 1989 Beneteau First 35s5. The prop is very pitted and suffering from lack of maintenance. PYI, Inc., the manufacturer, can refurbish the prop for about $1,000. When they install a Max Prop, they cut off about two inches and four or so threads off the end of the prop shaft. Will a fixed prop attach to our shortened shaft? Don't know until the prop shop sees the shaft. Then there is the other issue of the taper length of the shaft and the bushing issue of going from 25mm shaft to standard 1 1/8" bore of fixed props. The French didn't make it easy. We go back and forth on what to do.
sounds like you need a new prop shop! plenty of metric bore props on the market. adapter is bad advice.
Great video! You always have great information. Thank you! I am currently installing my motor from electric yacht now. Well actually building my battery box now🤗 so close so stoked to be on sailing with some regen with my fixed blade prop. Any advice on electric motors, wiring, how much you tax your batteries, how long you run your generator and what battery charger you use. We really appreciate your advice. ⛵✌
Awesome! I will get you detailed info shortly.
Brief info is:
4 years on our first batteries, 0.5 years on our new batteries.
Charger is Delta Q IC1200
I keep the regen set to “5” as this gives the least drag with regen still on.
I also set the motor limiter to 30-50% when we are not in a marina so that we have more fine control of the throttle setting. In a marina, I raise the limiter to 70% of maximum power. In really tight places I take off the limiter so we can use all the power available.
@@RiggingDoctor wow! That's great to know. And makes great sense. Thank you. I'll keep you up to date we have a 1973 formosa ketch, she also has full keel. I think we will share similar results. Thank you for your time 🤙
Trailing a fixed blade prop does rotate but it doesn't turn the motor, it just freewheels the gearbox
Depends on the setup. Ours does spin the motor as we move through the water.