A plank transom

[HarryH]

I'll be planking my lobster/picnic boat with 3/4+" strips per the designer, who also called for a 3/4" ply transom, in part to accommodate the amateur builder, I guess. I am a fairly skilled woodworker, and am thinking the Wana planking stock I have drying, being sort of a cross between Teak/Cypress/Mahogany, would make a strong and durable transom. Makes nice looking brightwork, too.

How should I build it? I can size planks to 1" in thickness and nearly 8" in width and still avoid sapwood. I need some guidance on building up this stern, I.E., preferable width of planks, and how fastened together: spline, batten, dowelled, other? I am using resorcinol glue elsewhere and would probably use it here.

The stern will be approx. 6'+ or so in beam, with some tumblehome, and about 30" from bottom to top of camber.

I am interested and will appreciate hearing from any and all who have done this...much thanks.

HarryH

[Bob Smalser]

Know what species the wood is so it's properties can be evaluated?

This flat, rift or qsawn stock?

Transom has how much curve in it from gunwale to gunwale?

[Bruce Hooke]

Bob, he seems to be identifying the wood as "wana," which I have never heard of...

[Bob Smalser]

I think this is it:

http://www.deepwaterventures.com/woods_wana.html

Same weight as H. Mahog but a bit weaker, stiffer, softer and much less stable. Also somewhat unreliable in air drying. Likes to check. Which usually means it's also subject to check in seasonal movement over time.

Same seasonal movement as Doug Fir, which means to me at first blush that q-sawn is a requirement for the movement to be compatible with framing size and cedar planking stock....and that double planking requires some thought, especially if there's a curve in the transom.

[ 04-14-2005, 06:43 PM: Message edited by: Bob Smalser ]

[mmd]

Assuming that the boat is inboard-powered, not outboard...

Transoms in smaller boats usually have thicker transom timbers than the hull planking so that plank end fasteners have sufficient material to land in. This is not so critical if the plank ends are glued, but it is still reasonable to beef them up a bit. If your hull planking is 3/4", I'd suggest that the transom planks should be 1" or even 1-1/4" thick. Transoms take a fair bit of wracking stresses, so a bit of overkill will ensure longevity. If your transom gets to be 1-1/2" thick or more, laminate it up in two layers, staggering the seams by a half-plank width.

Transom planks are commonly blind-splined or dowelled at the seams, and wide planks are not usually used because they have a tendency to split. I'd suggest widths between 4 and 6 inches (max), depending on the tendency of the selected species to split. Alternate end-grain radial rings orientation to control cupping. If the transom is wide (say, over four feet), consider installing vertical cleats off-centre on the interior to stiffen the structure. These are often in line with, and connected to, the engine bed longetudinals.

Remember that the upper outboard corners of the transom is the spot where rot is most likely to start. Make sure that your joinery between transom, hull, clamp, quarter knee, and any other structure in that location is tight, and that there is no place for moisture to get in. The area is notorious for not being able to be ventilated adequately, so build in rot resistance. You'll not get much chance to inspect it after the deck goes on.

[HarryH]

Yep, the Deepwater Ventures page tells the story on "Wana"...in fact, I got the stock from Brad himself, who supplies the same to Gannon & Benjamin on the Vineyard, among others. Nice stuff, exceeding straight and knot free, pretty rot resistant. Grain can be a bit wild here and there, and I will rip it to sizes needed before planing.

I forgot to mention a salient fact as Bob noted: it is flat transom, though raked. No curvature. Inboard power.

Michael, those are the construction details I am looking for....I will rip planks 4" wide or so then. It is spec'd to be 3/4" (in ply), so if I go the double plank/staggered seam route, which seems attractive, I will plane the stock to give a net 1" ormore thickness in the finished product. Other comments are noted and appreciated, too.

I will pick over the stock to get the best looking grain I can. I do not find it easy to pick out straight grain or rift sawn stuff in "mahogany families" or such because often the annular rings are invisible, very faint, or do not stand out in the dark material. Any tips, Bob?

Thanks,

_H

[Bruce Hooke]

Originally posted by HarryH:
I do not find it easy to pick out straight grain or rift sawn stuff in "mahogany families" or such because often the annular rings are invisible, very faint, or do not stand out in the dark material.There was what I thought was a good article on this in issue 172 of Fine Woodworking magazine (Sept/Oct 2004).

[Bob Smalser]

I go through all my mahogany boards on sawhorses in the sunlight and draw the end and face grain I can see in pencil to seperate them. Dunno about your stock, but most H. Mahog I'm getting around here originally destined for the music wood trade has a lot of grain runout also hard to see, and I get surprised occasionally when bending it.

Grain runout isn't as big a problem for you as seasonal movement, and I'd want to talk to builders used to it, as from the numbers it is not a simple, direct substitute for H. Mahog.

In a hard-to-dry wood subject to checking, double planking using two layers of stock makes the most sense to me. I haven't done it, so I'd email Dave Fleming who has done a lot of it. Two thin layers move almost as much as one layer of the same thickness but without the same force as the layers are attached but usually seperated by felt and bedding compound..the fasteners providing some "give". I'd alternate cups even in riftsawn stock and stagger the seams.

Make sure your moisture meter is corrected for temperature and species (I'd use H. Mahog because of similar density) and that the pins are penetrating to the center of the boards. 12% is ideal and I wouldn't use anything over 15% without more drying time, as it's gonna dry to under 10% sitting in the hot August sun.

I grew up with thick galvanized drifts bedded in white lead in 1 1/2" solid oak transoms and still use bronze drifts even when I glue the board edges....I just don't glue the drifts into their holes but drill them after layup and bed them in red lead covered by bungs or plugs. That way even with the worst-case crack or hole I still have a reinforced structure on both sides of the damage, and the drifts provide no additional crossgrain glue joints that promote cracking in wood that likes to move. Ain't lightweight construction tho, where that's a consideration.

[ 04-14-2005, 11:31 PM: Message edited by: Bob Smalser ]

[HarryH]

Great stuff Bob...thanks for the benefit of your experience.

Did not see the WB article mentioned by Bruce, but gonna take a look.

_H

[dcobbett]

HarryH,

Sounds like you are making progress. Any chance you could post some pictures so we could see what she looks like?
I have had no luck chasing down any leads on the location of Bates's work or a source for plans for your boat (Pogo).

[Bruce Hooke]

Originally posted by HarryH:
Great stuff Bob...thanks for the benefit of your experience.

Did not see the WB article mentioned by Bruce, but gonna take a look.

_HNote: it was not in WoodenBoat it was in Fine Woodworking...

[seayou77]

I have a repair looming on my Crosby Striper transome, the drift bolts make the job a complete replacement. Glad to read why they are there.
Re; grain in Mahog. I carry my LieNielsen rt. angle plane to the pile and clean a spot on the end of the plank. Can get an idea what grain exists in the plank without messing with the face of the board.

[Stephen Hutchins]

Sounds too thin to me. Is there a transom frame onto which this "planking" is built?

[carioca1232001]

mmd wrote:


Remember that the upper outboard corners of the transom is the spot where rot is most likely to start. Make sure that your joinery between transom, hull, clamp, quarter knee, and any other structure in that location is tight, and that there is no place for moisture to get in. The area is notorious for not being able to be ventilated adequately, Had I seen the "writing on the wall" above prior to leaving my boat out in the open for the bottomsides refastening and replanking , I would have definitely taken the requiste countermeasures in order to avert the wood decay you have painstakingly pointed out.

[HarryH]

Dave- I am making slow progress, as I am limited to a few hours per week it seems, what with chronic health stuff, a small house to run and a couple of teenagers who need lookin' after. No complaints though, as I love the process of building this boat. I took some time this winter to build a boat shed (Stimson style). Has been 75 degrees in there when it is 40 outside, so I am already thinking of opening a gable for spring.

Thus far, I have done all the lofting and made patterns of all frames, stem and transom, sawn all frames and companion cheek pieces, laminated the stem, and built, levelled and squared the building jig, which is 24 x 7'. ( And built the shed of course). I was hoping to have the boat set up before posting pics, but maybe I can find time to show what I have so far.

There is indeed transom framing, 1-1/2"x 2" all around the perimeter, with vertical cleats, etc.

Oops.My mistake Bruce.

I'm going to see if a plane will give me a shot at seeing the end grain clearly as suggested.

http://www.imagestation.com/picture/sraid164/pc607b01b376e851e3a6f7349c769dd92/f475d36e.jpg

[pipefitter]

If it is the bright wana wood you want to see on the transom,why not use one layer of ply with the solid wood over that? Wouldn't that add more stability?

[HarryH]

I did consider using plywood covered by planking. But my concern centers around plywood edges. Yes, they could be sealed, and perhaps I am putting too fine a point on this, but it seems to me a double plank glue up with solid lumber would result in a tighter interface between surfaces, as well.

Having said that, I am using plywood on interior frames, and the stuff I purchased from Maine Coast Lumber (1088 Meranti, $100 for 18mm) has turned my plywood reservations completely upside down. The local fir marine ply I've seen has plenty of voids visible in end grain, but this stuff is PERFECT, through and through, 13 ply with NO VOIDS OF ANY KIND or of any size anywhere in the whole sheet. None. Zip. Zilch. Nada. It's incredibly well pressed and glued, HARD, dense and heavy, to the point that driving fastenings into it can be a chore. In fact, threads hold better in it than solid stock of similar thickness.(I sheared off a few STEEL screws with improper pilot holes). How well will it hold up over time? Dunno, but I'd bet much better than any ply I've ever seen or used.

_H

[pipefitter]

I had the same reaction to the 1088 stuff as well. Was nice to work with it.Could also start out with a thicker planking and router out the inside to take a ply insert with the end grain of the solid wood exposed? I dunno.just a thought,maybe too much trouble and I guess solid would suffice afterall. I just like laminating over plywood. I have a hard time finding quality lumber here on the west coats of FL. I have to order across the state for meranti. I did find nice mahogany for frames tho.

[Bob Smalser]

Easy enuf to edge your plywood with 2"-wide solid to protect those edges.

But laminate anything that moves more seasonally than stable Teak, H. Mahog or cedar to plywood and you are asking for big, big trouble without consulting somebody who's already done a lot of it successfully.

I'm a little nervous about the movement numbers of Wana for a conventional solid transom, let alone laminated to plywood. If I didn't get a warm fuzzy from the supers at yards who've used it...

...I'd spring for H. Mahog.

Thta doesn't mean it isn't going to work just fine....book numbers and actual practice can sometimes be two different things on woods that haven't been studied a lot....but I'd sure do some consulting before risking an expensive mistake.

[ 04-18-2005, 09:49 AM: Message edited by: Bob Smalser ]

[pipefitter]

Yeah,I don't know about the wana wood either.I saw a ply /solid wood lam where they used solid edging outside the ply that was shaped like the last frame before it but I agree that it would be better to use mahogany for whatever you use in your build up. I just never liked laminating where the grains go in the same directions.I think single layer splined would be better than that. With substantial opposite grain stiffeners to keep the whole thing flat no matter what you make it of. Maybe is why the designer said to use ply. Apparently there must be some kind of substantial framing back there that makes the ply he recommends stout enough.