Canvas and tar boatbuilding

I recently have attempted a sharpie build that can't afford to stay in the water for long enough durations as to swell each time it is used, and am considering a solution I had read about on small boats concerning double plank with a sheet of 10 oz canvas between the layers. Supposedly, I'm supposed to smear both sides of this canvas in bedding compound, which could end up being really costly given a bottle of life caulk is looking around 27$ now. I mainly was thinking asphalt roofing tar (Henry 208, which claims its good even underwater) as such bedding compound, so I can actually turn a profit on this boat. Any suggestions?

 

It will double the weight of the boat. There are different techniques used in the past, including muslim bedded in shellac. They all assume the planking is tight. It would be cheaper and better to double plank and glue with epoxy. For a sharpie, plywood would be the best solution. What do you mean by "attempted a build"; did it fail?

 

no, the build is going strong. I just don't want to say I did it until its done.

Anyways: so I should use shellack instead? or paint? And why muslin?

 

You should first tell us some construction details. I will assume traditional plank on frame, but the devil is in the details, since there are many ways to make such a boat dry, especially if she's not finished yet. One of the simplest is to glue the seams and apply a layer of fiberglass. Or go with a ply bottom.

Roofing tar is way down on the list, right next to white lead and canvas.

 

I try and build in a more traditional style hence the double plank scenario: pictures are attached. I had done some reading online about Tomas Asa's skiff, from which I got the idea of double plank with muslin smeared in bedding compound -- what bedding compound was't specified, so reading some Pete Culler, I came to the conclusion that "black shingle stickum[his words]"=bedding compound , and (interpreting black shingle stickum as Henry 208 roofing tar) that I could therefore have decent success with tar on my current boat

 

Forget the roofing tar. The traditional bedding for double planking was white lead paste, the "black shingle stickum" would have been coal tar. Both products aren't really available today.

If you want to double plank, use 5200 (or similar flexible PU/PS) without canvas.
For the bottom wich I presume you will plank transverse, split the plank thickness in two, install in one go with overlapping seams. For the sides, sand them down to the fastener heads, add 1/4-3/8" boards with copper roofing nails.

 

Back in pre WW2 days Uffa Fox was building International 14s with two layers of mahogany.Between the layers was a skin of oiled calico.The workmanship was of a very high standard and some are still sailing almost ninety years later.For a basic boat that is kept out of the water,gonzo is quite correct,plywood is the better option.Given the state of the build progress it could still be the solution for the bottom.Seam battens on the inside might have been a viable option for the sides but it would be a bit of a pain to add them now.

 

so use a modern adhesive to goop up the canvas . . . . I heard 5200, but what is the consensus on other compounds, like butyl rubber?

 

I've also seen patented deigns for pine tar soaked muslin for between double plank, which sounds sketchy

 

I wrote "without canvas" above, but to avoid miscommunication: you don't use any form of canvas with 5200 or similar, just the stuff from the tube. Youtube has plenty of "5200 bottom" content, watch some.
If 5200 is to expensive, Loctite PL S40 is 9.78$ at Lowe's. If that's also to expensive start searching for free truck inner tubes on craigslist.

 

Changing construction methods half way through the build is a bad idea. The simplest, cheapest and most durable solution is to fiberglass the outside. You could do tight seams, which require a fair amount of skill fitting them. One method is to use a tool that crushes the fibers on the middle of the plank at the seam edge. You then plane off the wood that was not crushed and is softer. The crushed wood will create a seal with the crushed wood from the previous plank. The edges must fit absolutely tight. There is also a glued seam method: Glued-Edge Carvel Planking – Mastering Skills with the WoodenBoat School https://skills.woodenboat.com/articles/glued-edge-carvel-planking/

 

I hate the idea of glassing the exterior. I like most of Gonzo’s posts, but one sided glass is a bad recipe for boat in n out and wet bilge.

Use a PL sealant; take @Rumars advise.

Or follow the glued seam approach Gonzo shared…

my 2 cents

 

Hello Gonzo -- I kinda think glued planks are a little too new a method for my taste. It may be viable, it may be the future, but is way to far above my skill level And no, I am not shifting construction methods halfway through. I built this far knowing I could either approach the next step before me either with Asa Tomson's double cross plank method or normal cross plank method.
Rumars-- thanks for the 5200 suggestion, and I've done some research on it, and really like the idea employed in both 5200 bottoms and setting canvas in 5200 (which is apparently what they do at IYRS. ) I think its the best idea so far
Wet feet-- do you know what oil was used on the calico? Were the Internationals able to remain in the water for extended periods of time. Their record of ninety years of the canvas lasting has me impressed

Thanks for all the advice so far: I'se soaked up every bit of it!

 

The planking looks pretty thick. For double planking on a small skiff each layer may be about 1/4". The Aschcroft method would work well too. I am confused though. At the start you said the boat would never be in the water long enough for the planking to swell, but now want it to stay in the water for extended periods.