The effects of Cavitation - Ventilation
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- Опубликовано: 17 ноя 2017
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I am giving a short explanation of the effects of cavitation and ventilation on a boat propeller. This is a simplified explanation for a very complicated effect.
Changing out my water pump and noticed it was ripped apart. Didn't know why till stumbled across this video. My propeller has all kinds of nicks and wear and tear all over it. Now I know why ! Thanks for the video !
Been boating for years good explanation
You taught me something new, ole timer! Thanks for the video
Great video and explanation mate!
Thank you for the taking your time to explain it!
Thanks for commenting. Stay Well !!
very well explained by you and understood well on this end because your explanation of a complicated physics situation was applied and demonstrated on the prop with your fingers on the edges. I've heard this explained a 1000 times by very well informed and knowledgeable people, your explanation visual demonstration best by far. thank you.
Happy to help. Thanks for watching.
Thank you for this. I’ve found myself confused trying to understand this concept. Makes perfect sense now!
Happy to help thank you for watching.
I have had a few people ask about this. Thanks for watching
Very well explained.
Thank You
Best video on RUclips!
Yep. It helped. Thanks!
Wow man thank you, super informative
Great explanation. Thank you!
Thanks for commenting. Stay Safe.
really enjoyed the information thanks for sharing
Thanks for watching and Stay Safe!!
Much Thanks 🙏🏼 from down under 🦘
for your Considerate Sharing.
My late På used to say that if yà don’t learn something per day, it was just a waste.
I bought a trailer boat recently kitted for moderate seas 🌊 & your info’ builds muy Confidence 🖖🏼🍻😃
Be Well, YåLL🙏🏼
Happy to help and thanks for the kind words. Stay Safe and I hope you have a lot of great days ahead.
Om Fishing Ü2 🖖🏼😃 🎣 🌊
Great explanation! Thanks!
I am happy it helped. Thanks for watching and commenting.
I like people like that smart and simple and knowable not too many people left like that
Thanks for the great video! How will I know if my engine is mounted too high? What are the clear signs that the propeller is getting air, even a little bit?
Great job. I am a newbie and you explained this very well
Happy to help. Thanks for the feed back.
Thank you. Best explanation I found.
Glad it was helpful! Thanks for watching and commenting.
You're the man!
Thank you and keep watching.
Great explanation.
Thanks for watching and commenting!!
Good Stuff...Thanks
Outstanding explanation
Thanks for commenting and watching. Stay Healthy!!!
You have cavitation a little backwards. The vapor bubbles are formed at the leading edge of the blade and collapse at the trailing edge. Cavitation happens when there is a lack of net positive suction head NPSH. In the case of a propeller, NPSH is obtained by the speed of the water, towards the leading edge of the blades. This is why high pitched props, cause cavitation during hard acceleration. Once the boat is up to speed, the cavitation goes away.
Hey hey Jeff your the Chieff. Pretty good doh clear and slowly, way to go
Hey, thanks
that bottom end has seen some rockatation lol
😂😂
Good explanation...its something boaters need to know.
I agree thanks for commenting!
@@OmFishing Good stuff...thanks.
Lovely video,,thanks to you sir
Most welcome Thanks for commenting.
ty om finally i understand
Thanks for watching and Stay Safe!!
Hi there,
I am new to boating, I have a concern about my boat I still couldn't figured out. I bought it used the engine is 5.0 Murcruiser I/O with 220HP. It's not getting the speed. Once I watched your video I learned about cavitation. Do you think this is the problem I am having too. I know my prop is pretty bad shape. What would you recommen for me.
Thanks
Sam
Thank you
Interesting information. Great description! I have a 40 horse force motor. Short shaft. When I am at full throttle, I get what seems like occasional Misses.
I do have some slightly chewed up edges on my prop. Do I have a carburetor issue or might those Misses be cavitation?
I think ventilation maybe. Anytime you have places on the prop can be a issue. I would make sure I had new spark plugs and clean fuel first. Than look in to the other.
What pitch prop are you running? I have tried running a 14 on my 30 evinrude and it ventilates on take off and if I'm following behind another boat where the water is aerated. Do you think moving up to a 15 pitch would help
I am running a 10x15 on my 30 hp evinrude.
You shouldn't be running a 14 pitch on a 30horse. Try an 11 or...12 pitch max. 9.9 diameter. And also pay attn to your trim. If its not power....just drop it down a hole. You'll usually lose about 2mph top end for every hole in but boat will handle and turn better. And stay on plane at lower speed.
As far as a 15 pitch The only way id ever run that much prop on a 30 is if it was pushing a super light and skinny jon like a 15 foot tracker with a 42 inch bottom and absolutely nothing in it but me. . there's no benefit to that much prop except you might eek out 35mph wide open with a boat that weighs nothing.
You’re a smart man!
Thanks for watching and stay safe.
Thanks for that wisdom, that is why stainless prop are better yeah?
Thanks for watching and as always Stay Safe!!
Thank you for the info. I just put a “prop guard” on my 200hp Yamaha. At slow speed its fine but over 20 mph it starts listing the boat hard (23footer). At about 25 mph I thought it was going to completely roll over. Any idea what is happening and how to correct it?
My first guess is the motor is not mounted straight and the prop guard brought it to your attention.
Thanks for that description, also that is a very worn looking outboard leg!
If I can use that motor enough to wear the leg off I will be a happy man.
I couldn't agree more.
hello i m from croatia.. i have old johnson 60 on a smal plastic 4.20 meters boat. the motor is put in corect hight but the problem is when i go from standing still to full trotle boat instantly jumps in plain but then goes in high rpm like it sucked air or the prop is sliping. but when i go easy on trotle lets say 10% every 5 sec i can get to 100% trotle without any problem and at 100% max rpm is 5600... realy dont know what 2 do. prop is 11 3/4x17 aluminium and i m mising CONVERGING RING on it. is it posible that its sucking exaust in and velntilating? tywm for any information :) ps. sory for my english
I really am not sure on that one. Is their a chance the motor is just to big for the boat it is on. Don't know just asking.
5600 RPM is higher than I would rum an engine. Try a 19 or 20 inch pitch or just run it around 4000. You'll get better fuel economy around 3500 or so anyway. Also check the tilt of the motor, if the water is pushed up over the surface of the water, it is probably set too high.
What's a meter 🤣
Metre. About 3 Feet
great video thank you. could you please tell me if hydrofoil would be beneficial for my 6hp 4stroke outboard? its on a 10ft inflatable dinghy. some say hydrofoils are only good for 10+ hp outboads anything smaller is a waste of money and will slow down the boat.
If you are having trouble with getting on plane it might help if the engine has enough power to push through the water with the hydrofoil helping to lift. My boat would get ventilation when just running straight ahead. That is why I installed mine.
Can boats with a lot of seagrass grown on it experience ventilation? It feels like mine is spinning in air on top speed because it goes much slower than before it was so grown under the boat.
The growth on the bottom of the boat can change the drag in the water. I would clean the boat before I start to change a lot of stuff.
Great explanation...although no water is turning to steam. It's just pockets of air or a difference in high and low pressure creating an absence of water.
Still...thank you.
HI MAYBE YOU CAN GIVE ME SOME SUGGESTIONS ON AN ISSUE IM HAVING. I HAVE A JOHNSON 30HP AN I HAD TO MAKE A HARD TURN AN I GUESS THE MOTOR VENTILATED, BUT NOW WONT START. WHEN TRYING TO START IT, IT SEEMS TO BACKFIRE FOR LIKE 3 SECONDS THEN CUTS OUT.
Back fire when starting is a lean fuel problem most of the time. When you made the hard right you probably suck up some trash in the fuel line and might be in the carb.
@@OmFishing I TOOK IT IN FOR SERVICE, WHAT HAPPENED WAS I SHEARED THE KEY ON THE FLYWHEEL AND THREW TIMMING OFF
so why does surface propping work so well then isn't that a ventilated situation? I surface prop sometimes with the prop half-submerged and go faster...
Surface propulsion is half the prop is in the water the top half create a ventilation and the bottom half propulsion. The key point here is half the prop in the water and half out.
I have one of this dory! I just purchase a brand new Yamaha f25 tiller motor. The dealer wanted it to charge me 300 dollars to install the motor, but I was painting the bottom and doing some modifications on the inside. I went by what the manual and the Yamaha dealer recommended on how to install it. They required that the cavitation plate is level with the bottom of the transom. So I did and when I took the boat out for the first time with my brother in law going out and being out there was perfect until we started heading back in we noticed the motor propeller slipping my brother in law said its sounds like it’s cavitating. I have a 20” transom with a 20” long shaft. I thought maybe it was because my brother in law is a heavy guy and he was standing right in the front of the bow. so when we hit any small wave the propeller was coming out of the water. He said it shouldn’t do that. I email the Yamaha owner and send them pictures of my installation and he said he was going to pass the pictures to his worker guy. It’s been a week haven’t heard anything. I want them to reinstall it to see if it would solve the problem. When I took the boat yesterday out for a ride myself to see how it rides with one person it was a horrible ride if I tried to go fast at all. The bow would stick really high and any little wave felt like you hit a rock and it was scary. I just want to sell this boat and motor if I can’t fix it. 🙁
Don't give in so easy. It could be the hull design that is causing the problem. You might have to get the long shaft. Maybe you could fine a longer shaft motor and try it. I know they use them a lot on pontoon boats because of that problem.
Try to trim the motor on the mount; push the prop out to lower the bow when running without the front load(person)
Balance on small boats is everything. Boat at cruising speed should have a slight bow up orientation.. Trim your motor in. Till you find sweet spot.. And some boat hulls are just poorly designed. So they will ride like garbage no matter what you do
Seiko SKX007. I've had the same watch for 15+ years.
I like mine. I have had it about the same 15 years.
How does surface drive work
Surface drives use different propellers much higher RPM. I don't know a lot about them I am more of a salt water person.
Atmetferic pressure is around 15 psi, water boils at 100 degrees, when you apply a absolute vacuum lowers Atmetferic pressure water will boil at aroind 20 degrees.
Thanks for sharing your knowledge.
Lookin at the lower unit of this outboard....He's still got a lot to learn! It's beat to #hit! Maybe he should learn how to take care of his outboard....
Looks like mostly shallow water soft bottom . My outboard looks the same way motors are over 20 years old as well could have been previous owner
Thank you for this good explanation. Why can't USA hurry up and change to the metric system :)
Thanks for watching and stay safe.
That prop has seen some sand. Mine looks the same
40-50,000 Dollar prop ! OMG!
I have looked at use props for over $20,000. I can't even afford the prop let alone the boat.
The majority of the bubbles is exhaust.
Your right I was just trying to give a short explanation to a very complex subject.
All of the bubbles are exhaust, the vapour bubbles immediately revert to water when they leave the low pressure zone.
Not all the bubbles my friend. SOME... just some, are my flatulation bubbles.
You can feel the difference
You sure can feel the difference the prop will not work with air around it. That is why boaters get in trouble around a water fall. The prop sucks air and the current sucks you in. Stay Safe!!
Simply, ventilation is sucking in air, cavitation is boiling water.
Thanks for watching and Stay Safe!!
What will cure burp cavitation. I can go at full throttle then you will hear a burp and the boat hesitates slightly. This only happens at top speed. 4.3 l8tr with alpa one drive 200 up hydrofoil did not help.
That is not a easy answer. Problems like that can be hard to solve. You might have to talk to a prop shop. Does it do it with a different prop?
@@OmFishing I am using original prop. Only time this happens is at top speed the only thing that I see is maybe I am raising out of the water as not much of the boat seems to begin the water. Can outdrive be adjusted down farther or in.
We are creating a 'kayak' site for marine/boating parts and accessories to help people find the best deal vs. having to go to lots of individual stores to research - we may also provide links to content on youtube such as yours so people can also get advice.
What do you think about this idea? Do you think it is a good idea for yourself/your audience? We would like to get some feedback before we get too far down the road.
If you do like it, is it the kind of site that you would feel comfortable advising your audience to check out?
Thanks!
Cheers,
Steven
Email me at omfishing@yahoo.com
At sea level atmospheric pressure is 14.7 lbs/sq.in
14.6959 actually
Cavitation is pockets of vacuum causing implosions, not pockets of steam causing explosions. Aeration is when there is air in the hydraulic system, basically what a prop submerged in water is, that compresses and the energy is lost through the compression of air.
ruclips.net/video/ON_irzFAU9c/видео.html
Your an idiot
Your prop shouldn't be spinning while you're putting it on the trailer.
I am by myself a lot and I use the outboard to run the boat on the trailer. Then I just get off the bow and drive the truck up to the parking area. Thanks for watching and Stay Safe!!
@@OmFishing I also launch by myself, and I have never run my prop while loading the boat. Yesterday I loaded without a dock by myself, and I didn't run the prop while loading. I also didn't get my feet wet. The prop should never be turning while loading the boat.
What are you talking about. Just drive it right on the trailer
When I am fishing by myself I just back the trailer in the water and run the boat on with the outboard motor. Check out my video (Fish oil fishing on the ICW {at 6:30 minutes} you will see me do it.
Or you can check out my video Running the Evinrude 225 Robalo Boat Project 60