Nutshell Questions

[Clinton B Chase]

Hey Nutshell fans. I am building a big Nutshell this winter and would like to show off with some very pretty brightwork. I would like to have varnished transoms and a varnished sheerstrake. My question is, Should I use plywood or butt together a coule 10" wide pieces of nice mahogany hardwood for the transoms? Can you get a super pretty varnished look off plywood? How have folks joined two boards for a transom blank? Any tips for finding a good piece for the sheerstrake in terms of nice grain, etc. for a varnished finish?

Cheers and thanks,
Clint
Portland, ME

[JimConlin]

Talk to the good people at Maine Coast Lumber (http://mainecoastlumber.com/) in Westbrook (and York). They have a good selection of high-quality boatbuilding plywoods and represent them honestly. What you order is what you get.

[LLaver]

You could use a light ply for the transoms and laminate a layer of solid timber onto it.

Lee

[ishmael]

Most ply has a rotary sawn face veneer which doesn't look all that nice varnished, to my eye anyway. You can buy it with plain or rift sawn face veneers, but you have to ask and maybe order it special. If you go with the ply transom I think it would be worth it. But, the other problem with a ply transom is that you are going to ding it at some point, and the face veneers are almost paper thin these days.

All in all, I think I'd go with the solid mahogany, or if weight is an issue hunt up some nice cedar. Though lighter in color it takes a lovely bright finish.

I've not looked at the nutshell plans. How is the transom fastened?

[Rod Tait]

We are currently building a whitehall with a solid cherry transom. It may be a bit overkill for your boat but we have some photos on our site gallery.
http://www.orcaboats.ca/photopost/showgallery.php?cat=521

[Bob Smalser]

Prams have relatively big transoms. What you can get away with in a 10" wineglass transom may not work in 22" crossgrain expanse of pram transom.

Your glued lap plywood planks won't more at all seasonally.....but a solid transom certainly will, and the wrong wood glued and screwed to those planks will crack. Q-sawn H. Mahog and the cedars are the most stable but are still a risk....especially when the paint is neglected later in its life.

I'd use marine plywood, either face-cut mahogany or DF I overlaid with 1/8" mahog veneer got out on BS and planer. Marine epoxy, of course....the most flexible and forgiving of glues.

[ 10-12-2005, 02:05 PM: Message edited by: Bob Smalser ]

[ishmael]

Bob's point is well taken, which is why I asked how the transom is fastened. However, the Whisp I built, similar width in the transom boards, glued lap planking and a glued cedar, plain sawn, transom hasn't had a problem. The side planking is glued and nailed to the transom. It's been through the moisture cycle repeatedly.

I assume it's because cedar doesn't move much, and the transom was well sealed.

What do the plans call for? White knew his business and when in doubt follow the designer.

[Bob Smalser]

Regardless, if you do glue up a solid transom, then also drift it properly with bronze rod and if it cracks, it'll be no big deal...stuff some 5200 in there and go to the movies.

Without the drifts, if it cracks, the crack will get larger, even to the point of requiring transom replacement, because you won't have any backup structure to support the loads there.

[Ocean Spray]

Clint . . . . my brothers and I built three Nutshell Prams,
two with plywood transoms and one with solid .875" Hundoras mahogany transom and bow. The wood was recycled from an old carved sign. The boards were glued up horizontly using biscuits. Other than that it wasn't any different building the hulls using .75" Okoume plywood for the transoms.
The solid wood does stain up and varnish a little better than the plywood but not that much. We also stained and varnished the sheer strake after fastening a
rub rail to the top and bottom of the strake. For the sheerstrake we just used the .25" Okoume that was spec'd out in the instructions.
I'd be glad to e-mail you photos of what the different boats look like as well as give you some building tips,
especially after building three boats.

[Clinton B Chase]

Tx for thoughts all. Joel White wants a 3/4" mahog plywood for transoms, but his boats are also historically painted all over with little to no varnish. I do not see the reasoning behind the concern with cracking if screw holes are predrilled and the boat is built properly with healthy epoxy glued laps. I have rowed/sailed these prams and have found them to be unbelievably stiff...meaning hardly any flex -- not flex really-- at the transoms. Moisture won't be an issue since it will be dry sailed and stored inside and carefully maintained. I will look into these different veneers for the mahogany ply and I liked the idea of considering another wood for the transoms. Cedar perhaps...howabout longleaf pine?

Cheers,
Clint
Portland, ME

[Bob Smalser]

Originally posted by Clinton B Chase:
I do not see the reasoning behind the concern with cracking if screw holes are predrilled and the boat is built properly with healthy epoxy glued laps. .... I liked the idea of considering another wood for the transoms. Cedar perhaps...howabout longleaf pine?
It's the solid transom that's gonna move while the planking stays put. The difference in those shrinkage rates, less the amount of "give" in the planking, can be always measured in the size of the resulting crack...and glued plywood has almost zero "give".

http://www.woodbin.com/calcs/shrinkulator.htm

You can figure this out for any wood you want to use...for flatsawn Yellow Pine, one of the worst, your 22" transom will move almost 3/4 of an inch from kiln dried to 18% EMC in the water.

So it'll swell significantly, straining your glued laps, then when it shrinks that 3/4 inch again, it will move faster that those glued planks can adjust and it will crack. I guarantee it using SYP.

Q-sawn H. Mahog, under the same conditions will move only a quarter inch, which should work for you if the boat is well protected. The cedars are similar...but very soft and will get dinged up quickly.

Also, enuf solid mahog to do your transom will cost close to a hundred bucks. With 15 dollars worth of marine ply and a 20-dollar mahogany board, I can easily resaw that board into 8th-inch veneers to make a transom I know will last the life of the boat under any conditions. Those 8th-inch veneers will move seasonally, too, but with much less force than 3/4" solid boards, and they won't overcome the flexibility of the epoxy.

[ 10-13-2005, 02:06 AM: Message edited by: Bob Smalser ]

[JimConlin]

If you can't find an appropriate plywood and are daunted by slicing veneers, another alternative is to buy some 1/16" veneer. In either case, i'd vacuum bag it to the ply. I'd prefer any of those to solid stock on a plywood-planked boat.

[ishmael]

Digesting all of this, I think I'd buy a sheet of ply with a nice face veneer. It'll be a bit pricey, but a single 4x8 will get both transoms. It'll obviate the movement issue, and will look good with varnish.

[Bob Smalser]

That wood movement table I posted is linear, hence worthless at over 20% EMC where moisture and movement are more geometric, and also a bit of a generalization when it comes to boats.

The denser the wood is, generally the wetter it will be and the slower it shrinks and swells. In equal weather conditions, cedar will be drier than spruce and H. Mahog, which in turn will be drier than D Fir....and etc to SYP and oak.

Around here, topside D Fir in a moored boat varies from 6% EMC in late August to 15% EMC in January. (the reverse of most climates) In a transom, the submerged outside planking remains at around 25% and the dry inside at 18%, with 25% throughout in bilge water. Lower those numbers for cedar and mahog and raise them for SYP and oak. Pull a boat out of the water in August after its been there a couple weeks and you can see the potential problems from all that unequal EMC....and why just anything in the lumberyard can't go in your transom.

If the boat lives in your garage 99.9% of the time, less of this applies. But it's never a good practice to build any boat with the assumption it'll live its whole life dry sailed...and be well cared for, to boot.

The best practice is to build for the water, not the trailer. Build for the water, and it'll take some abuse and survive.

[ 10-13-2005, 02:01 AM: Message edited by: Bob Smalser ]

[StevenBauer]

I glued and screwed 1 piece plywood planking to a 7/8" solid mahogany transom on my John Gardner skiff and it looks fine 5 years later.

Clint, do you have any need for some clear vertical grain fir? I've got a bunch that's 3/4" by 2". 12 to 16 foot lengths. Salvaged from some porch flooring I tore up in Cape Elizabeth.

Steven

[Rick Tyler]

Originally posted by StevenBauer:
do you have any need for some clear vertical grain fir? I've got a bunch that's 3/4" by 2". 12 to 16 foot lengths. Rats. Wrong Portland.

- Rick

[Clinton B Chase]

Well, I am definitely going with hardwood transoms on the pram. I am considering Spanish Cedar instead of mahogany to save some $ and a little weight. I understand that this is not a true cedar and shares many of the durability and aesthetic benefits of H. mahog. Any reason not to try this wood?

Cheers,
Clint Chase
Portland, ME