strongest joint for a transom

[austin57]

what's the strongest joint for two mahogany planks to be used for transom on a shellback dinghy. I've got a biscuit jointer so could use that; could also use a spline joint or rabbet the two planks - any suggestions?

[Steve Lansdowne]

While I can't find the article at the moment, I read (in WB?) some time ago an article that indicated that just plain edge to edge with no spline, rabbet, or biscuits is the way to go. You might do an search of the WB Index.

[hokiefan]

Don't have any personal experience with them, but I've heard on here many times that bisquits are bad in a marine environment.

Bobby

[JimConlin]

Biscuits, spline or ship-lap are all weaker than a straight glue joint. If you apply, and keep, a good finish on the wood surrounding the joint, the glue joint is stronger than the wood..

[Rob Hazard]

Biscuits are typically made of Beech, a strong wood, but one with with little rot resistance.
I'd go with a plain glue joint.

[sailboy3]

On the boat I'm working on now, I used oak splines which seem to work just fine.

[RodB]

Why not add a spline or a few dowels... and epoxy...

RodB

[brad9798]

Edge-to-edge ... with dowels ...

In my experience in ANY woodworking, this seems to work out!

[Scot L T]

Biscuits, spline or ship-lap are all weaker than a straight glue joint.

That is very true with modern glues but unless one is using an adhesive that has gap filling properties (ie. epoxy) then the wood to wood contact must be tight, tight, tight for the glue to have the required bonding strength. That's where one must take the time to make that joint perfect. Do not depend on the glue to fix a shady joint.

The most common failure of the glue line (meaning the joint fails because of the glue not the wood) is at the point where the glue meets the wood. For one reason or another the glue does not attach itself to the wood. This could be contamination, wrong glue for the wood, joint is glue starved or most often sloppy wood to wood contact which leaves a gap that the glue does not have the strength to bridge. Also knife cut joints have more strength than sanded as there is less damage done to the fibers of the wood if they are cut rather than sanded.

I think it's interesting that one almost never sees a spline in antique furniture. Those old guys really knew their stuff so they must have had a very good reason for choosing not to do it that way.

I'd say go with the well made joint and no biscuit or spline.

[David G]

For this application a straight butt (rubbed) joint is as strong as anything, more likely to be durable toward the end of the boats life-span, and will be easier to repair - if it comes to that. Do you have some specific concerns about a butt joint?

[Terry Haines]

Dowels or biscuits may help keep joint aligned during assembly.

[David G]

Dowels and biscuits will help keep the joint aligned during glueup, esp. dowels. However, when it's not desirable to have either of those (as in this case), it's quite easy to throw a couple extra clamps (C-clamps, or the like) on to keep things aligned.

[Svensk]

My choice is a half lap joint. Gives you more glue (epoxy) surface, long grain to long grain. My second choice would be a full length spline of the same material.

[Bob Smalser]

Structural marine glues only date to WWII. Before then the edge joints were often bedded in white lead and drifted together, the drifts "toe-nailed" slightly to hold the boards together.

http://pic20.picturetrail.com/VOL12/1104763/6583947/379754457.jpg

Even today using modern glues, a few well-placed bronze or galvanized drifts driven after assembly can help distribute the load of an outboard or rudder to all the boards in the transom instead of just one or two glue joints. And after a serious bash to the stern by another boat or a rock, the drift reinforcement may make the difference between limping home and swimming.

http://pic20.picturetrail.com/VOL12/1104763/6583947/379754975.jpg

[peter radclyffe]

you can use less than half lap, say quarter with bronze or copper dowels
so half lap from face
quarter lap from edge

[Nicholas Carey]

Don't have any personal experience with them, but I've heard on here many times that bisquits are bad in a marine environment.Bicuits are compressed beech.

Beech is not exactly rot-resistant. The point of biscuiting or splining long grain edge joints is aligning the boards. I believe Lamello makes plastic biscuits, tho.

[David G]

Lamello makes plastic biscuits, and metal ones.

Some of these schemes are perfectly do-able. None of them are necessary. We're talking about the transom on a small (Shellback) dinghy. If you want to do something beyond a simple butt joint, just to practice up on your joinery skills, go right ahead. But know that there's not much to gain, and - with some of these schemes - there are drawbacks. Some involve added expense (silicon bronze drifts?). Others, I've mentioned already. I would think that this would be a situation where KISS rules :)

[James McMullen]

For a boat as small as a Shellback Dinghy, anything other than a simple edge-to-edge glue joint is an extravagance--unless you are using this boat as a practice run for something more complicated and want to try out something more elaborate on a small scale. Biscuits are the worst idea, though, as the biscuit pockets the cutter makes are bigger than the biscuits themselves to allow for a little adjustment, and the last thing you want to do is build in a few voids into your transom. Useful though it may be for cabinetry, a biscuit joiner has no place in structural boat building.

What I would do? Run the mating edges through a jointer, spread the glue and clamp. It'll be stronger than the surrounding wood.

[Harbormaster]

I've used one of those router bits designed for glue joints for a couple of mahogany transoms and it appears to've worked out fine. Joint the pieces first, run the router and glue. They are self aligning and I haven't had any problems.

Of course, just a plain butt joint has worked too.

[ssor]

Probably a finger joint if you could achieve it.

[ChaseKenyon]

go for show on such a little transom.

cleat the boards alternating front and back with nice tapered butterfly keys out of the same stock one third the depthof the actual boards.

It can't come apart and it will look really cool. You could even go with stain and bleach like some speedboat decks to set the keys off even more.:cool::cool:

Just a thought from a fellow woodworker.

LOL

Remember I'm the guy planning on building a Septagonal Gazebo one of these summers. Why you ask? Simply because I Can.:)

Chase:D

[Eric Hvalsoe]

For a small mahogany transom on the kind of boat your talking about - you're gluing long grain - a simple edge glue joint is perfectly adeqate. Of course as long as you handle the glue and the surface of the joint competently. I tend to add short dowels, merely for alllignment. You could spline for allignment, bur that is adding nothing to the strength of the joint.

[Bob Smalser]

I'd sure take Peter's suggestion to cut up copper or bronze rod to use as dowels, if that's what you intend to use.

http://pic20.picturetrail.com/VOL12/1104763/6583947/84779985.jpg

Because unless you make your own or buy from a specialty supplier, common hardware store dowels are made from a wood from SE Asia called Ramin, which looks good but rots while you watch. Just like beech biscuits do.

And while I don't disagree that all a small transom requires is a common edge joint properly glued, if I were building a shellback I'd probably use three, quarter-inch bronze drifts. Two from the top and one from the bottom. It's faster than marking and installing dowels or a spline, and it's definitely the strongest joint.

[gert]

Lamello buiscuits can swell enough to telegraph their location; particularily with a gloss finish. Trust me, this does not look good.

[deltabrent]

I'm currently having the same debate with my dad regarding a 16 ft inboard launch we intent to restore. Total transom replacement is needed. I vote on a slight bevel to the joint just to add a bit more surface to glue to. He wants to put in a quarter inch plywood spline.
I say no to plywood in a solid wood transom (Yellow Cedar).

Would the bevel make any difference than a squared edge joint? I'd do it through the jointer.

[JimConlin]

A bevel would be hard to keep in alignment when clamped.

[Dave Gray]

Doesn't the Shellback call for a plywood transom?

[austin57]

the shellback plans do call for a mahog. ply transom but buying a sheet of 3/4" ply for a 18"X36" transom is a budget buster, especially when I had a nice 4/4 plank on hand that fit the bill. am I looking at unforseen problems not using the plywood?

[Bob Smalser]

the shellback plans do call for a mahog. ply transom but buying a sheet of 3/4" ply for a 18"X36" transom is a budget buster, especially when I had a nice 4/4 plank on hand that fit the bill. am I looking at unforseen problems not using the plywood?

Not really. The transom is sufficiently small and the mahogany sufficiently stable that seasonal movement differences are negligible.

[ChaseKenyon]

one

http://www.woodworkersjournal.com/Uploads/Imports/PublicationsArticle/MOW/193_2009_JanFeb/193SBB18.jpg

http://www.customcabinetmakers.com/pictures/join/cobut1.jpg

http://www.customcabinetmakers.com/pictures/join/sbut.jpg

http://www.woodworkingtalk.com/attachments/f2/6030d1229625825t-butterfly-inlays-split-boards-img5449478bdbdb27bff.jpg

http://www.rockler.com/images/articles/01_Planing_Key_lg.jpg

:D