27' Ocean Master transom rebuild

[Billyclub]

Hi everyone. I've been lurking about for awhile and finally have a question and am looking for some guidance. I am rebuilding my transom that was very wet. I am going to complete this transom from the exterior and not the interior. The core has already been removed when I took the boat out of the water last fall. I left the inner skin intact so the boat would not deform. I have received a lot of information from may people but this forum keeps coming up for an excellent knowledge base. I know that the exterior approach is not the standard way but It was by far easier but I believe I can make up the strength by enclosing the transom (currently a notched transom).
I plan on using BS1088 Okoume, two 1/2" pieces that will sandwich a 3/8" piece in the middle. My first layer that is in the layup schedule will be a layer of 1.5 CSM epoxied to the inner layer. Then the first of three layers of marine ply will be epoxied to the CSM. I am using System 3 Gel Magic for the adhesive between layers of plywood. Should I apply a layer of glass between each layer the plywood? some say yes others say it's not needed because of the Gel Magic and the bond it offers. Next after the 1/2" will be the 3/8" and then over that will be another 1/2" plywood. I need to stay under an 1.75 thickness for fairing and blending considerations. I plan on finishing the lay up with 2-4 layers of either 1708 or whatever the consensus recommends.
The inner outboard well will be trimmed and all gel coat removed. Two knees will be extended for the top of the new transom ply down to the stringers in the bilge where they will be tabbed into. I additionally will layup a horizontal member that will bridge from port side to the starboard side on the interior side on the new transom. This structural member will most likely be a laminated piece of several layers of marine ply to approx. 1-2" thick and 4-6" wide. When the inner transom components are all glassed in they will resemble the letter "H" only the horizontal reinforcement will extend the entire transom width.
What do you recommend for the outer layup schedule of glass? Was thinking 1708/ CSM / 1708 / CSM then fill, fair and paint. Is that enough glass on the exterior?
I am having a Bracket built by Custom Marine Welding in Miami. The platform is 70" wide and is a floatation style bracket.

The engines are a set of 1998 Johnson 200's Loopers. Each engine weighs 440lbs.

A lot to read, sorry. trying to give everyone a clear picture of my project

[Billyclub]

137 reads and no one?

[XstreamVking]

The glassing between layers is only going to add strength. Especially if you run it past the wood onto the old fiberglass surfaces on the hull. I have done many transoms where I replaced the outer skin that I removed. re-bonded and glassed around the edge. If this is not possible or not what you want to do then I would build it up with 1700 biaxial glass. You want about 1/4'' of glass where you mount the motors and bracket on the outside of the transom. Using the 3/8'' ply will only leave you with approx 3/8'' inches for glass total. I believe you might want to consider using more glass between the two 1/2'' plys and leaving the 3/8''ply out. You are hanging a lot of weight and power on the back and it would only be stronger with more glass. A 1.75'' transom is fairly thin for a dual motor bracket system. Most would have a 3'' transom for that application. Interior structure sounds good the way you have it described.

[XstreamVking]

And some might wonder why most won't bother to respond to queries from one time posters.

[spbutler]

Send pictures.

[XstreamVking]

Wasn't patient enough to wait 24 hrs, he won't post any pics now. Long gone to another info source...

[roadkill636]

^^^^^

I agree. Looong post with no pics . Not worth responding to.

Just like another NEW member here that starts a new thread every few hours about the same boat and motor... nope not responding to thoes

[RobF]

guy next door has one, we talked about full transom and bracket.

Issue, with his at least, is the drains were direct out the transom and already AT or slightly below waterline.
A full transom and bracket presents a few issues- first the drains themselves, they will likely have to go THROUGH the bracket then out the other side. Bigger issue- those drains will likely always be below waterline.

Is your boat set up the same?


aaaaaaaaaaaaaand I just read the other responses lol. oh well I typed this out im leaving it
would be nice when someone asks for advice especially if its a problem that they reported back what happened/if its fixed, etc