Hollow vs. Solid Mast S2 E66
HTML-код
- Опубликовано: 17 июн 2022
- What you need to know before you make a wooden mast. In this episode of the Art Of Boat building, Bob Emser Boat builder guides us through his decision to build a solid mast for his Haven 12 1/2.
“If you’re going to make it, make it beautiful.”
Bob Emser
Birdmouth Calculator: duckworksmagazine.com/10/howt...
Boat Building Clinic:
bob-s-school-e7ca.thinkific.c...
"How to Build a Wooden Boat" David "bud" McIntosh
www.amazon.com/Build-Wooden-B...
Subscribe for more Boat Building from The Art of Boat Building:
ruclips.net/user/bobemser...
Share this video with a friend:
• Hollow vs. Solid Mast ...
How to support The Art of Boat Building.
Purchase Official Merchandise here:
www.bonfire.com/store/the-art...
Become a Patron:
/ theartofboatbuilding
Watch next
Recommended Playlists
Carvel Planking Playlist:
• Carvel Planking
Haven 12 1/2 Playlist:
• Season 2 - Haven 12 1/2
Tool Making:
• Tool Making
Let’s connect:
Facebook:
/ bobemseramericansculptor
Instagram:
/ artofboatbuilding
Twitter:
/ bobemser
Linkedin:
/ bobemser
Bob Emser American Sculptor:
www.bobemser.com
Video equipment used:
CanonM50: amzn.to/2TVob5l
Takstar SGC-598 (shotgun mic): amzn.to/2ZSVmup
Saramonic Lavalier Mic amzn.to/3drnZCK
Disclaimer: Some of these links go to one of my websites and some are affiliate links where I’d earn a small commission if you make a purchase at no additional cost to you.
#theartofboatbuilding #artofboatbuilding #makeitbeautiful#woodenboatbuilding #buildingasmallboat #buildingasailboat #shipwright #toolbuilding #Haven12 #herreshoff #shipwright 
Хобби
I'm a naval architect, been building sailing wooden boats for the last 20 years, restored, own and sail a Rival 32 on which I build a cedar hollow mast, along with a cedar boom and spreaders, which are in use for the last 15 tears. never had a problem with it. The core is reinforced at the base, about half way to the spreaders, at the spreaders and at the top. It's been coated on the interior and exterior with epoxy, all the glued joints are also epoxy. All thru bolts are predrilled and fitted with stainless steel tubing epoxy glued where the bolts fit into. electric wiring goes thru the interior from bottom to top, all running and hoisting cables are exterior running with guiding holes on the steps fitted along the mast, this steps are a easy way to inspect the mast at all times. The construction is a simple case with 4 sides and planned to shape. simple and robust, overall it saved about 30% of the weight. The mast is 36 feet long and I can lift it alone, with some difficulty but still can.
I have a bit of a confession to make. I don't build boats. Probably never will. Don't even know if I want a boat.
But, your videos are always interesting and very calming.
I guess you could say I'm using your videos as some sort of theraphy or means for destressing.
Just wanted to let you know. :)
Ditto.
In my youth most masts were wooden, rectangular in section, hollow and stayed. Most were also tapered. Very few seemed to be sealed inside and without epoxy, 'sealing' would have been limited to a coat of primer. They lasted ok and when they did rot, it was usually around fittings and penetrations. From an engineering perspective a hollow mast can be stronger and lighter if properly engineered. I have built solid and hollow masts - the choice driven by boat type, use and scale (wall thickness is determined more by the need to resist impacts than rigging loads on a very small mast). If your trying to earn a living boat building, solid will be favoured every time - its so much less labour.
One thing I have learned about Bob in the time I have been watching him is that he extremely talented, organized, and he always he has the proper tools to complete his projects. The proper tools are only as useful as the craftsman using them. Bob is definitely an expert. I just love watching him!
I'm a structural engineer so immediately your question of hollow vs. solid was intriguing. In bending which I think is the primary stress acting on the mast, a hollow cylinder is virtually the same strength and stiffness as solid. I watched to see how you built the mast and it seems that building it from 2 pieces is quicker and less prone to problems that building it out of 8 strips. I don't think the savings in material is worth the complicated joinery. You appeared to have gotten 2 good pieces of wood to build from, the advantage of building with smaller pieces is that you might have a better chance of getting 8 uniformly good pieces of small wood than 2 uniformly good larger pieces. This would likely be more true if you were building a significantly larger mast. In building construction you've likely seen composite materials such as glue laminated wood beams. These are significantly stronger than a beam sawn from a large piece of lumber because each small piece can be made up of uniformly good wood, a large piece is more likely to have variations that would reduce its overall strength. However I think even if you were building a significantly larger mast it might still be better to laminate boards flat than to join them to form a circle. Something you didn't address about the methods of building the hollow mast- how do you taper it to 2/3 of its diameter at the ends? It seems that the material would get too thin at the ends to work with.
Easiest way to do it is to gradually reduce the width of the dovetail piece as it gets closer to the top, just take a mm off the flat face every 10cm or so, for example
If you are really looking for performance then you could also reduce the thickness of the piece but personally I’d prefer to keep the internal thickness as the diameter gets thinner,
"best" ... after all is said and done, IF you don't need electronics up in the mast, THEN go with the strongest / most efficient / cost effective, BUT if you NEED electrical up in the mast, there are some sacrifices well worth the trouble in order to have a way to get that wiring up there....just a thought, I haven't heard addressed here. success, I too like your videos very much, thorough...complete...thanks
hey so i have a question, for a 19ft long sailboat, replacing the mast with a wooden one. for that length of a boat which would be about a 22ft long mast, could that be made from a single piece of lumber or would joining two pieces like in this video be better? the boat was salvaged and the alum. mast is not so hot. i would like to make one out of wood
@@jamessawyer8744 assembling from smaller pieces has a strength advantage. you can select enough small pieces without flaws to put together into a larger piece but you would have difficulty finding a single large piece that was high enough quality wood.
@@billj5645 awesome thank you so much
Always a pleasure to watch (and learn).
Wow I really liked the belt sanding device. Definitely stealing the idea for my future boat.
Wonderful. Thank you so much for showing us your stupendous work, time and again.
Oh, so many tips and tricks! Thank you, Bob! I really appreciate it.
As always instructive and entertaining.Thank you,Roly 🇬🇧.
Ooh! He said "Next Boat"!!
I really enjoy your episodes. Especially the in depth analysis and explanation of the decisions you make.
Of course there will be a next boat. You didn’t expect him to stop now, did you? And after the second one there will be a third, a fourth, etc.
I have a pine mast on my Grundel 665 witch is sawed longitudinally in two parts, the sapwood core has been removed and the two halves are glued together, so this has been for over 45 years a very flexible good mast!
such a joy watching your art taking shape.. thank you Bob for sharing.. fair winds always
Thanks Bob that was a very informative show. Great to see a mast from start to finish.
great stuff. I always pick up something from your videos. Thanks
Man, you're so good at explaining stuff! Very informative. This was beautiful to watch take shape and I look forward to future videos as always.
Neat trick drill sander. Love watching your work
Thanks for another great episode Bob. That inside out belt sander is the cat's meow! And nothing like having a handy 16 ft. aluminum I-beam lying around. What a great shop you have. Thanks for sharing your project with us. - Don from a little town on the Erie Canal.
I'M HERE FOR THE SPRUCE!! As an instrument builder/Luthier here in Australia I am eyeing up your beautiful Mast and Spa grade Stika. Really hard to get here fortunately I got some recently. I enjoy your channel and your knowledge.
Really fantastic work, Bob! Nicely done! 😃
Looking forward to the next part!
Stay safe there with your family! 🖖😊
I'm not surprised you went with solid mast. It looks great. 👌
Oh that Sitka spruce! What beautiful wood!
nice job on that mast bob...looks good .....perfecto as usual..
Good job, Bob. Real clear look at the pros, cons, and process.
Thanks Greg!
Wow! I'm extremely impressed with your woodworking skills. Taking that square mast to a smooth diameter with a planer and some sandpaper is amazing to watch.
What an artist! That boat is turning out to be beautiful and you named her. That mast turned out much lighter than I figured it would. Very nice job.
Hey Bob, just discovered your videos and they have me very inspired. I just finished watching all 65 episodes. I am a complete greenhorn when it comes to boats, or boat building for that matter, but there is something therapeutic to watching you build this boat and the Aero from season one. Looks like you have christened your Haven 12 1-2 the 'Skylark'. Thank you for the thorough explanations of all the steps you use to accomplish your floating art. It may be some time but I will eventually build my own sailboat and I will be using your videos as a reference. We have quite a few lakes to put into here in NC and learning how to sail and building my own boat has just been put onto my bucket list. Thank you so much!!
No question that this small gall rigged boat was best fitted with a solid mast. I built a Herreshoff Marco Polo back in the early 70's and the three masts were designed as hollow tapered box spars. They were an awesome project...we sorted through MANY units of spruce to find good 11 rings per inch vertical spar grade planks....and then scarf joined the 20'ers into 55' long boards from which I could cut the rabbets and tapers. They turned out quite nice, two other builders had me make their spars as well.....So I did it 9 times. Mine, I did all with hand planes...but the commissioned ones, I purchased a power plane. Gotta say, the time spend using a hand plane was well spent, the lines of the spars were truly sweet....and it was good PT as well.
-Veteran '66-68
Nice work there mate. About 10 years ago I made a new mast for my 28ft gaffer, it was solid with a 30mm hollow that I use for cables to mast head. I purposely didnt seal the indide but allowed air flow from both top and bottom by using a fashioned cap on top . I figured that if any moisture gets behind any fittings and could potentially start to rot, that the air flow insde the mast would help out. 10 years later, no problems what so ever.
I used resorcinol glue and also no issues so far.
Thanks for sharing your work, cheers
Very nice, Having carried lumber as a carpenter for a loooong time I thought it was going to be around 28 lbs but I included paint🙃 thanks for posting enjoy your trip to the east coast!
I would be very curious to see “destructive testing” of solid versus birds mouth masts. The grain direction and knots have very large impact on strength. With a solid mast it would be impossible to align grain direction in 360 degrees and very costly, if not impossible, to avoid all knots. I built a 12 foot birds mouth mast with NO knots and all straight grain aligned perfectly in all directions. Once the jig was set up all sections were cut in far less time than shaping a square chunk, with less waste.
Rot from within can me mitigated by coating the inside with epoxy while gluing up.
Btw the glue up was very easy as the pieces fit together like a jigsaw.
I actually don't do woodwork. But i know from steel work the rule about hollow structures:
A pipe is stronger then a rod *if* the cross section is identical. Same cross sections means identical weight (with identical materials, of course). *But* , you have to increase the outer diameter. As long as pipe and rod have the same OD, the rod will always be stronger.
The calculation get's more interesting the other way: You can get the same strength with less weight (but still, larger OD!).
In vehicles this is quite often justified for shafts and sometimes axles. In boats it might with regard to center of mass.
Just what I was looking for. Thanks for such clear explanation.
Glad it was helpful!
Very instructive. From Malta.
Agree on the glue joint. Titebond III wood glue is a “intrusion” resin, made to be “injected” into the wood via clamping pressure. Epoxy, on the other hand is surface held, meaning it “grips” the surface instead of being forced into the microscopic cells of the wood.
Good move.
That analagy makes sense! The clamping pressure forces the glue into the wood pores! Thankyou👍
@@chrisleggatt3240 S
(means smile)
Bob a great episode. I have to admit a little hope that you were going to build a hollow mast, just to see all the glue-up. But this solid made explanation was terrific. Have a successful how next weekend. Wish I could be there. And thanks.
Found your channel from the Acorn to Arabella discussion at the boat show. Looking forward to seeing the build!
The belt sander trick is a touch of brilliance.
Sorry, but will probably miss you at Mystic, but look forward to the live broadcast! Can’t wait to see this beauty in the water!
Thanks for the great video!
First video I’m looking of this channel. Immediate subscribe
Love the MCM doors on your shop!
very nice work and informative
I enjoyed that, thank you (I'll save my life story for another day)
Vary vary nice job on your mast!!!!👍🏻👍🏻👍🏻👍🏻⛵️⛵️⛵️
I'm excited too see you build the tender "Victoria" ✌♥️
Loved watching this 2 to times
That was great! Thank you!
Nice way to round it off!
Hi Bob - really great mast - well done! Just one comment to your intro about spars structures. Hollow masts labor, in comparison to the whole boat work effort, is not really significant. They are also not really difficult to assemble as you suggested - there are number of approaches as you know and just one more step for boat building that is fairly complex itself. The main advantage of various hollow masts is that you may rearrange the wood structure to get given properties in term of long and short distances, there is also problem with availability of proper wood for long solid spars. But anyway, I was absolutely impressed on your approach to this issue and final product - brilliant work. Take care and sail safe! Kind regards from Poland, Pawel
Brilliant technique
Ok, from a structural engineering point of view all of the material at the center of a solid mast isn't doing very much to make the mast stiffer and stronger relative to it's weight - just heavier. On the other hand from a material point of view with a solid mast all of the fibers of wood are all aligned and bound together as perfectly as possible - but perfect trees are rare these days. Solid masts are probably the simplest and most reliable and is easiest to control degree of stiffness and bendiness by controlling the exact profile of the taper. You can see why Yankees at least prefer a solid mast if performance isn't crucial.
On the other hand, with a built-up mast you can cut out all of the flaws in the wood and optimize the inside and outside diameters to achieve your desired balance of stiffness and light weight but requires a much higher degree of craftsmanship and engineering. With a built-up mast your joints also have to be pretty flawless. The birds-mouth mast gives you a greater glued area than the coopered mast and may have some structural advantages over a straight joint - but I don't think anyone has ever actually tested that. In either case, a built-up mast is *a lot* more work. Cheaper? more expensive? hard to say.
Amazing. Great viewing...cheers..rr Normandy, Fr.
Hi Bob, just seen your boat building Vido on the Contruction of the mast. I noticed that you glued both sides, i was taught that you need to only glue 1 side. I built a 12 ft. cedar "stripper" several years ago. Bob wonderful job. see you next week.
Bill Rees
Hilton Head S.C.
You have a beautiful shop, Bob. And, another great video. How many times did you have to sharpen the blades on the power plane while making the mast?
Hi, this is my first time watching your channel, and so far I'm loving it!
I just wanted to say that there is a better way to set up your saw horses to ennsure that your aluminum beam is even straighter. It's very late where I am, and I can't find the exact formulas that I'm looking for, but I will try to sumarize as best I can. I will also post an update with the exact formula when I'm able to find it in my books. To put it simply, to get the flattest line with a beam supported on two points, subtract 31.5% (total guess that I'll fill in with the math later) of the beams overall lenght from each side, and place the support there. The second formula is for a beam with the least deflection (different from the straightest line). It's the same principle, but the % of total lenght subtracted from the ends is slightly different. I apologize for sucha long comment that has no conclusion, but I will do my best to update with the correct information as soon as I'm able to.
I look forward to a lot more time spent watching these great videos. Take care!
Matt, I happy you're enjoying the videos.
As for the aluminum beam deflection I think you way over thinking a simple set up. The mast weighs 23 lbs. Most mast makes don't have a I beam and generally just use the straightest timber they can find.
"...don't look for perfection. We're not building a Steinway piano. The goal is good old-fashion workmanship"
-Greg Rössel, MasterBoat Builder, "Building Small Boats"
Thanks for watching!
Cheers,
Bob
Beautiful, and really fun to watch
Wow ! Good thinkin’
Built a couple of Bolger’s boats w/my Dad, worked at Legnos in Groton CT, and studied naval arch. in school. It would’ve been nice to actually test some varying sections (torsion, shear, bending) modulus and failure strength, but in general the strength contribution of the section is provided by the outer edge, with very little by the core. As noted by others, failures are common at bolts & fasteners or penetrations so sealing is key. Without ANY actual test data at hand, my instinct is that: 1. Laminating evens out anisotropy (differences in strength by direction). 2. Hollow is only marginally weaker, maybe not significantly, in repeated failure tests. 3. Hollow allows wire concealment. The particular joinery is mostly aesthetic, but I’d use a hollow section with epoxy and seal every surface. Great workman’s, btw!
Very nice!
Very enjoyable video. Just curious as to why you placed the clamp handles down instead of up on the glue-up? Also, glad to see your Wen planer. I bought one as a throw-away for one project, yet it has really held up and performs better than my old Makita. Still going after many projects.
Fascinating. I always thought Masts were one continual taper.
I have clamp envy!!
I recognized those clamps as the same as mine. When it comes to clamps Harbor Freight is your friend. Just check them for alignment before you put them in your cart.
Great piece of wood you got there fella.......I hand made some vertical grain Sitka Spruce oars with Wenge tips for a 16' skiff I made in 1985 and still going strong. That mast should be a around a long time unless you hit a LOW bridge! OUCH! Why dont you protect the sides of SKYLARK with packing blankets so you dont ding her by accident when moving lumber around?
Thank you Bob for the video. Excellent and beautiful work as usual. Having built a 23' birds mouth mast many years ago, I definitely prefer the glue up of pieces for a solid mast. I was curious what the center of your sanding drum was made of. It looked like discs of rubber or rubber bands. Can you let us know what you used there? Have a great show this next weekend.
Hi Matt,
Yes, the traction drum has rubber bands on it. ( I meant to mention it in the video and just forgot) One could use an old inner tube, I had rubber bands so I thought I give them a try since I didn't have any inner tube rubber. Well it worked fine so I keep it. I may replace the rubber bands if an inner tube finds it's way into my life. The Drum need rubber on it so it has more traction that the friction of the belt sanding the wood.
Thanks for watching!
Cheers,
Bob
28:00 That is one fine tool. Very Clever.
Hello, Bob ‐ thank you for the amazing content! You're attention to detail and accuracy is outstanding!
My only concern with this episode is that you used an aluminum I-beam to construct your mast. Aluminum beams are NOT straight or flat. Unless you had your beam precision flattened/straightened, do not rely on it for accurate construction of your boat.
Skylark is looking grand, throughout the episode. Soon to have a mast.
Hi,
Thanks for sharing your knowledge. Is there a known difference between Titebond 3 and epoxy in terms of aging ? Do we have experience about it ?
Best wishes
I was looking for a hollow mast build but never mind !
I like the inside out belt sander, I was thinking about turning the mast using skate wheels as steadies in the same sort of way that you have your supports. Mind you, your way you can make an oval mast. Now, a tapered oval hollow mast, there would be a thing !
Yes, in fact it is a thing. My friend Steve, who has done my 3D modeling and metal lathe work, built an ice boat many years ago. His mast is not only tapered but in cross section is egg shaped with the thick edge being the leading edge.
He use the same method it did to get the results.
Thanks for watching!
Cheers,
Bob
Replacing rotted stringers in a 16ft fiberglass factory boat i realized how much rigidity was gained by the closed cell foam. Wouldn't filling a hollow mast with foam help keep moisture out as well as create a little more strength? I'm not a sail boat guy. I'm retired and want to stay that way.
23 pounds - unexpected - though I did notice how easily you moved the unshaped lamination. I was wondering about the titebond III grab after coating both boards as you slid the top plank into place. Is a solid mast less rigid/more flexible than a hollow mast? (And everybody should have a 13’ I-beam straightedge for those big clamping jobs!
Doesn’t the sandpaper also take material off the carrier spindle changing the mast sanding area and possibly altering the taper from round to oblong? Do you do a final check of the diameter and taper?
You could always cut a channel in the roof to accommodate mast installs. 😄
The spindle attach to the drill has a rubber coat. In my case I used rubber bands ( hence the multiple colors) so it has traction. It does not change size. As I mentioned in the video it is best to go at a moderate rpm and turning the spar as you go. This is important as it would be easy to get the spar out of round. Takes a bit of practice and paying attention.
Great question! As for suggestion of cutting a hole in the roof, I think I’ll pass on it 🤔
Thanks for watching!
Cheers
What astonished me is that you mentioned pine/spruce. I always thought it was hardwood that was used, as cornefirs are less strong. I am wondering if american cornifers are fine for mast, woudl European pine would be good as well?
Also I thought mast, if glued, would be glued from 4 pieces to prevent any kind of wrapping.
How did you orient the glue plane with respect to the boat? Fwd-Aft or Port-Starboard?Spectacular work Bob. Thanks for sharing!
Forward Aft.
@@TheArtofBoatBuilding That is what I thought would be best - thanks for the feedback :)
Thank you.
thanks for the video QQ Can you estimate the "error" in the dimensions considering all this transfer processes involved ??? I guess +- 3mm/ 1/8 inch
There is another option in mast building which can be 5x stronger then a solid mast. That's a laminated one wite epoxy glue. The biggest advantage is its flexibility. Be safe and joyful building your boat.
Bob - I like your explanation of epoxy vs. titebond. I am hoping to make frames for my small boat by laminating oak strips that I have sitting around. I've seen this done with epoxy. If thats more of a gap filling glue than the titebond, should I consider laminating them with titebond instead?
Hi Weston,
Yes, you can consider using Titebond III.( make sure it's Titebond III for exterior use) As long as the laminates are clamped well and there is squeeze out.
Best wishes,
Bob
@@TheArtofBoatBuilding Thank you, Bob. Cheers.
I used to erect big tents and we used mostly fir poles. Tough as hell. We had a few old spruce ones left they were pretty beat up and old. It wasnothing for one gut to carry a 25 foot or 30 foot center or quarter pole by himself.
Is there any advantage to strengthening the mast by epoxying fiberglass or Kevlar spiraling strips up the mast?
Hi from Arizona Bob! Have you always preferred a hinged stick rule over a tape measure?
There are several reasons I use a folding rule. For short measurements, under 6, it is more accurate. In some cases for frequent short measurements it’s handy to leave unfolded. I do use a tape as well especially for long measurements over 6 feet.
I also grew up seeing my father always using a folding ruler so it’s a bit of nostalgia for me, it constantly reminds me for him.
Thanks for asking and watching.
Cheers,
Bob
I didn't catch you explaining why the mast is made of two pieces. Is it stronger that way, or is 2X4 lumber easier to find or less expensive in these lengths?
When you were looking for the mast timbers, was it possible to find quarter saw wood, or did you have to take whatever came in that length?
I think it works like this: Because the mast is round, one side will be quarter-sawn, then walk around it 90 degrees and it'll be flat sawn. So you can just rotate the mast for the best strength. Since he glued up two pieces, it would be good if they were both sawn the same way.
I purchased the Spruce from Johnson Workbench is MI. I ask for clear quarter sawn and that's what I received. Great people to work with.
Just looking at the drawing of the gaff rigged boat at 0:01 and I wondered what the advantage is over a straight up mast with a full triangular sail instead of the gaff boom.....I have a 125 dinghy and it's rigged with a long aluminium mast etc.
You cited densities for Douglas Fir being ~6% heavier than Sitka Spruce; These are natural products with inherent variations; it would seem to me, pretty likely, that these are close enough that you could actually find some Douglas Fir that is less dense than *some* Sitka Spruce...but you might have to search through a good-sized pile to find it.
Also, a factor in comparing options here is the cured weight of measurable quantities of adhesives.
The major benefit of a sectioned mast is your ability to have more uniform stength in different planes, versus the 'pole', which, even if you can get one that has grown quite 'straight', it is still a little hard to tell how symmetrically it has grown.
Assembling a sectioned mast can let you be more discerning in examining the grain structure and patterns, for symmetry/balance.
Personally, I like the idea of the 'birds mouth' joinery, as it rather functions as an integrated tongue/groove system...except for the part where the tapering is going to eliminate much of that, in the upper portion of the mast.
Unless you 3D modeled it, and had a MONSTER CNC machine!
;-)
Happy waves!
clamps are important to make sure you have enough clamps or a vacuum bag handle too
is there such thing as filling the hollow mast with a urithane foam or closed cell foam?
when are you planning to install the mast show making sails and rigging the 12 1/2 or did I miss some episode ?
Hi Larry,
No, you haven't miss it. Currently, I'm still casting bronze parts. Last week I cast the mast partner and the coaming clips. I'll be casting a mast cone soon. I'll be doing an episode on those bronzes soon. As for the sails I've ordered a sewing machine and the supplies for the sails. I hopefully will be sailmaking this winter.
Thanks for asking.
Cheers,
Bob
Very useful. A couple of questions: 1. You stated that the weight difference between solid and hollow was insignificant, but did not explain how you arrived at that conclusion. Just from looking at the proportion of space in a hollow mast I’d have thought it was 2/3 or less of solid weight. 2. I’d have thought that a birdsmouth spar would far easier to taper and to assemble than a coopered one (simply prepare rectangular battens with the desired taper towards each end before cutting the birdsmouth; no angles to maintain). Coopered staves risk sliding about in the clamps; am I missing something?
I wonder if you considered cutting the board in four in order to align the grain in different directions. Wasn't your wood quarter sawn?
No did not consider cutting it as the grain it so straight to would not have helped. And yes, the Spruce is quarter sawn.
There's more surface area glued together in the bird's mouth method, which ought to make it stronger. A friend and I made a 4 inch tapered mast, 12 feet long made from white pine 2x4s. Sitting on sawhorses at the very ends, I sat my 240 pounds in the center and and the spar hardly flexed.
I also made two masts this way from white cedar, each just under 40 inches long and about 7/8" in diameter, for a radio-controlled schooner. They weight almost nothing though I think I'll refrain from the sitting a fat man in the middle test.
If you did create a hollow mast, could you run lines internally - would that be a good reason to build a hollow mast?
Bob, how did you get your sanding belt inside out?
Hi Roger,
The belt does want to resist but with enough persuasion it will flip outside in. The first belt I used was a 3 x 18" I then tried a 3 x 21" which was much easier to convince to turn inside out.
Thanks for watching,
Bob
I built a goat island skiff and went hollow birdsmouth. I didnt have to calculate it but the build was easy. You cut the strips on a tablesaw and plane to taper on the flats sides. When glueing up i used epoxy and i taped off two of the joints on the first glueup. You just bind it with tie wraps it will lie straight. After the glue dries you cut it open and you have two halves. When i glued the final two joints i coated the inside and the endplugs with epoxy. When dry plane the corners off flush and you have a hexagonal spar which is where youd be after a pass with spar guage and plane. The OP here says the weight savings is insignificant but i disagree with that. Theres half as much wood. The condensatin and rot inside issue i hadnt heard of. Mine is only 2 years on so cant say but the inside is completely coated just like the hull. I made my yard and boom from solid stock milled square spar guage and plane and that was easier by a couple steps.
i wish i had all the tools and a palace of a shop.
To answer the question on at what point would a hollow mast make more sense than a solid mast: When the difficulty and expense to procure a solid clean and straight piece of mast wood outweighs your budget and time.
Bigger the mast the harder it will be to get an appropriate log. Laminating does provide a certain strength, but as you mentioned its life will be considerably shorter if not kept dry within.
Bob, interesting discussion, I have gone down the "birds mouth" construction (with taper) for the mast, for the boat I am building which is a clinker construction Ilur by François Vivier. I can concur its a lot of work.
What about filling a hollow mast with urethane foam? The foam is closed cell and would prevent water from gettin inside and it would provide some additional structural integrity although not as much as solid wood. The advantage would be overall weight. Your statement about weight was comparing sitka spruce to douglass fir but not hollow to solid.
A question if you please? I would have thought that ripping the Sitka Spruce into four "Quarter" sawn pieces would result in a stronger main mast joint than two pieces since you would be able to orient the grain for maximum streangth..
The spruce I have is quarter sawn and had over 50 annual rings in one inch. My guess is that sawing it into 4 section would not have added any significant strength if any. On my way to the Wooden Boat Show I’ll ask some folks more experienced than me.
Good question, thanks for watching.
Bob
@@TheArtofBoatBuilding thank you for sharing. Love the channel. ^~^