Transom Wood Selection

[propav8r]

Hey y'all, new boat owner here with a project, a 1956 Feathercraft Vagabond II.

I'm in the strip down/clean/polish portion of the project now, but I need to build a new transom for my boat. It's pretty simple, basically a long plank that runs the width of the transom on the inside, about 48" long by 7" tall, then two planks on the outside, each one about 8" wide by 14" long.

Ignore the rectangle on the right, someone put that there to hold a trolling motor, it won't be returning.

Mainly, I'm trying to choose a material. I'm lucky enough to have an exotic hardwood/plywood supplier here in town, and I have a few choices:

3/4" Mahogany plank ($35 total)
3/4" Sapele plank ($35 total)

The sapele planks have a tighter/straighter grain than the mahogany.

3/4" Sapele plywood ($164 for a 4x8 sheet)
3/4" Aquatek marine mahogany plywood ($130 for a 4x8 sheet)

I'm just wondering if there's a compelling reason to buy plywood over a plank, especially if I'm finishing the plank with a spar varnish or something?

A single 4x8 sheet of plywood would allow me to do the majority of the floors as well, but my initial pan is to get a sheet of 1/2" plywood for that, I feel like 3/4 is overkill for floor thickness but maybe I'm wrong.

I'm not really interested in Coosa board as it won't suit the look of the boat at all. The boat will be stored out of the water if that makes a difference on material selection.

 

[rolmops]

I would use marine grade plywood with eight ply layers.
The ply layers are made with the grain crisscrossing at 90 degrees for every layer whereas a wooden board has all the grain in one direction only. When the wood gets wet, the board may split length wise along the grain, plywood will never split. Believe it or not ,but plywood is stronger that a regular board. As for the floor. It depends on the support that is underneath the floor. If the distance between supports is small, the 1/2 inch will be plenty thick. But if there is no flotation foam support (by law there should be) and the distance is such that the 1/2 inch starts bending, then 3/4 inch is the better way to go.

 

[Scott Danforth]

I'm just wondering if there's a compelling reason to buy plywood over a plank, especially if I'm finishing the plank with a spar varnish or something?

because 2 laminated pieces of 3/4 plywood for the transom is many many many times stronger than dimensional lumber. its why engineered beams are made out of plywood and not dimensional lumber. you can also do 3 laminated pieces of 1/2"

I would go with the marine ply like rolmops states vs ACX for that barrel back.

1/2" for the floor is plenty, especially with the ribs you have in the second picture. you could go with 3/8" if needed.

did we mention that plywood is stronger than dimensional lumber

 

[propav8r]

Sounds like the 3/4" marine ply is the way to go then. I'd really like the woodgrain to show through, so I guess I'll seal it with spar varnish or spar poly.
The rear floors are easy, but I'll have to do some supports that run the width of the boat for the passenger compartment floors that are more of a V shape. Shouldn't be too bad.

 

[jbcurt00]

Mahogany or Saeple would look period correct and be significantly better looking.

Join the Feathercraft website & Facebook pages, invaluable resources for all things FC.

3/4" transom panel on inside and out on the transom

 

[propav8r]

Yeah, I'm on the FC forums as well, figured I'd post here for more eyes on the topic. No doubt the Sapele would be nicer looking.

 

[cyclops222]

Stained and sealed Exterior Plywood for the inside transom floor. And inside of the transom

How much HP are you going to put on it ? Will determine transom outside woods. Could be a combination of Ply, wood planks and a thick enough Aluminum motor clamping plate. Inside should have a plate to prevent engine bolts from chewing holes in wood. S S bolts with thick washers and locking nuts.

 

[JKLknik]

I would not hesitate to use oak it has been used for centuries to build boats and ships, and it is hard to beat the look of a nice piece of oak. Put several coats of spar varnish on it and you will be good to go.

 

[propav8r]

Stained and sealed Exterior Plywood for the inside transom floor. And inside of the transom

How much HP are you going to put on it ? Will determine transom outside woods. Could be a combination of Ply, wood planks and a thick enough Aluminum motor clamping plate. Inside should have a plate to prevent engine bolts from chewing holes in wood. S S bolts with thick washers and locking nuts.

It's getting a 40-45hp motor, likely a Mark 44 or Merc 400, something along those lines.

Here's the wood that came out, just mahogany (I think) dimensional lumber.

 

[cyclops222]

How many cracks are hiding under that 1" X 1" angle at the bottom of the transom ? The transom piece of Aluminum just looks very thin. There is normally a piece of U channel on the top of the Aluminum transom to prevent the thrust of the motor from bending it inward. It just does not look like it will survive 40 hp.

 

[jbcurt00]

@cyclops222 ever seen a Feathercraft up close?

Factory 1×1 isn't an addon brace, it's a mini trim tab.

FCs don't have a transom cap

Eothet 40hp mentioned is a great motor for a vintage FC