Replacing plywood with solid wood?

[MyReprieve]

I’ve recently purchased a 30’ fiberglass center console that currently has a plywood cored transom that is rotten due to the builder not sealing the penetrations. I bought it as an investment because I got a great deal due to the repairs needed, but it is a dream setup for my needs, so I really don’t want to sell it. I was planning on buying Coosa Board for the replacement of the rotten plywood because that is what all of the cool kids are doing, but I’ve got a large stock of African mahogany that I purchased to build a skiff and haven’t gotten around to.

My question for the masses: Does anyone see an issue with building the transom out of two layers of African mahogany instead of plywood? They are still building boats out of the stuff. I have driven a couple modern multimillion dollar yachts that were double hulled mahogany. It’s strong, water resistant due to oil content, and will be fully encapsulated in polyester resin and glass. Plus it will save me $3,000.00 in materials.

 

[alldodge]

Modern hulls still using Mahogany, haven't heard that but ok I guess

I would use ply or coosa, thinking the resin wouldn't stay stuck to the mahogany, but I'm no expert. Maybe @Woodonglass has an answer

 

[todhunter]

I used Sapele mahogany at a few key points in my build (like engine mounts) - resin and glass adhered just fine. It's how mine was originally built and there was no noticeable difference during the "gut" phase in how the original 35 year old glass was stuck to the original plywood vs. original mahogany.

 

[Scott Danforth]

Plywood can take a load from any direction because each ply is on the bias

Single direction grain like what you are proposing will take a larger load in one direction, and much less if a load in the other

There is a reason that plywood has been used for the past 100 years on transoms

As AD suggested, if you dont want plywood, look at coosa

 

[MyReprieve]

Double layer cold formed boats run the grain in opposite directions in much the same way plywood does. My thought is to run 2 layers of 3/4” planks with the grain opposing directions. Just think two layer high quality 1.5” thick plywood.

 

[Chris1956]

Isn't mahogany quite an oily wood? If so, resin will be a challenge to get to stick well. An old friend of mine had a 50's mahogany hull with fiberglass over the mahogany on the bottom. The fiberglass had a bad habit of peeling.

Stick with the plywood, would be my recommendation.

 

[KJM]

I'd use the Mahogany. Most of the strength in the transom is from the fiberglass, with the core more for creating an I-Beam effect. As well coosa board isn't as strong as either plywood or wooden plank by itself, but works just fine, I know because I just finished using Thermolite (very similar)in my transom and its solid as a rock. My stringers were made of mahogany (or some similar tropical wood and were still solid despite being wet for who knows how long. They were covered with fiberglass but the fiberglass had delaminated, but it was wet and made in 1978 so no surprises there. My point being that I doubt the manufacturer would have used the mahogany if FG wouldn't adhere as this was a well made boat. Just my thoughts.....

 

[Woodonglass]

Mahogany is just fine !! Wipe it liberally with Acetone before applying the pre-coat of resin!

 

[sphelps]

My problem with using mahogany is your covering up such pretty wood that you could make brightwork out of .. Ply is much cheaper ..

 

[todhunter]

My problem with using mahogany is your covering up such pretty wood that you could make brightwork out of ..

I hear that! I about cried when I laid glass over my new engine mounts. I only used it in places where screws were going to be used, though. On my tear-out, I was surprised to find the original center stringer was made of mahogany, but it did it's job. It was soaking wet and still a solid piece of wood when I pulled it out. The other 4 stringers were plywood and they were a crumbly mess when they came out.

 

[Ned L]

Teak is oily, .......... Mahogany? mmmmmm.

 

[Lectro88]

I hear that! I about cried when I laid glass over my new engine mounts. I only used it in places where screws were going to be used, though. On my tear-out, I was surprised to find the original center stringer was made of mahogany, but it did it's job. It was soaking wet and still a solid piece of wood when I pulled it out. The other 4 stringers were plywood and they were a crumbly mess when they came out.

That is Beautiful.
I know what you mean on crying when covering.
And I just looked at Mahogany 2 weeks ago, decided against it.

 

[MyReprieve]

Thank you to everyone who took the time to help with your input. I have decided to bite the bullet and paid the $1k for a 1-1/2” thick sheet of Coosa Bluewater 24. I just couldn’t stomach hiding all of that pretty mahogany under the gel coat and it will be a good selling point if I ever sell the boat that the transom no longer has a wood core.

 

[MasonK.]

I’ve recently purchased a 30’ fiberglass center console that currently has a plywood cored transom that is rotten due to the builder not sealing the penetrations. I bought it as an investment because I got a great deal due to the repairs needed, but it is a dream setup for my needs, so I really don’t want to sell it. I was planning on buying Coosa Board for the replacement of the rotten plywood because that is what all of the cool kids are doing, but I’ve got a large stock of African mahogany that I purchased to build a skiff and haven’t gotten around to.

My question for the masses: Does anyone see an issue with building the transom out of two layers of African mahogany instead of plywood? They are still building boats out of the stuff. I have driven a couple modern multimillion dollar yachts that were double hulled mahogany. It’s strong, water resistant due to oil content, and will be fully encapsulated in polyester resin and glass. Plus it will save me $3,000.00 in materials.

African mahogany is strong, water-resistant, and can be encapsulated in polyester resin and glass. However, it's important to consider factors such as structural integrity, weight implications, compatibility with resin and glass, long-term durability, and compliance with boat building standards before proceeding. But consulting with a Bluewater boatbuilding professional is recommended to ensure suitability and adherence to safety guidelines.