19 foot Offshore Power Dory Build #16: Crack in Fiberglass on Transom

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Blog entry by English posted 04-30-2017 09:07 PM 4415 reads 0 times favorited 2 comments Add to Favorites Watch
« Part 15: Perfomance Update. Part 16 of 19 foot Offshore Power Dory Build series no next part

Over the summer last year I noticed a crack developing beside my outboard on the transom.

The crack is where a butt splice was on the transom when I originally built the boat. I had built the transom for a 20” motor and when I received the motor it needed 21 3/4” to get the cavitation plate even with the bottom of the hull.

I considered several options for the repair. I considered removing the plywood off the entire transom, removing the 2×4 and the 2×8 and replacing them with a 2×12, installing new plywood, glass and repainting. I considered just adding a ½” marine plywood layer over the transom, glass, and repainting. I considered milling out the original patch and replacing it with a new patch that covers 3 more inches of the 2×8, re-glass, repaint. Not wanting to do this repair but once. I contacted fellow Lumberjock Shipwright. Paul thought the options I was considering, though effective, were a bit extreme. He recommended a very simple repair, to sand off the area around the problem and re-glass with a couple of layers of bi-axial or if I could find it tri-axial cloth. Make the patch a good six inches or more past the motor contact areas in all directions and make sure it more than covers the crack. Run a router down the crack at 5/8” depth to get to clean, dry wood and epoxy a spline in first just to seal the crack. So this was the method I chose to follow.

Here I have removed the motor, and sanded down to the epoxy.

There are 4 drain tubes in the area to be covered with Tri-axial fiberglass, so they will have to be replaced.

The crack can be seen here in the fiberglass.

I routed out the crack with a 1/2” router bit 5/8” deep which is the thickness of the marine plywood on the transom.

I installed 2 layers of 23 oz. Tri-axial fiberglass, this is the first layer.

After the first layer was wet out with epoxy, I put on the second layer overlapping the first into the wet epoxy.

Then after 5 or 6 coats of epoxy to fill the weave I finally got the repair area smooth.

Next I have to replace the drain tubes. The original ones were brass with flared ends. I never had a good feeling about the flared ends on the brass tubes, so this time I went back with PVC. Paul had recommended Using ABS pipe and sanding the outside with 80 grit. ABS is not available down here in the south smaller than 2” So after finding information on a West Systems web page on how to install PVC with epoxy I went with 1” sch 40 PVC, I first filled the old holes after the brass was removed with thickened epoxy. Then I drilled a 1 3/8” hole for the tube, but before the hole saw came out the far side I changed over to a 1 1/2” hole saw and drilled in 1/4” from each side. The 1 3/8” hole keeps the pipe in the center of the 1 1/2” opening to allow epoxy to get in all the way around the pipe to insure a positive seal. Here is my test hole in a 2×4 .

All of the tubes were installed using this method.

Then the boat was taped off and the three different paints were used to repaint the transom and the splash well.

At this point I just need to reinstall my motor, swim platform, depth transducer, and Smart Tabs. Then the boat will be ready for the water. I plan to let the paint cure for a few days before I re-install the motor.
I plan to install vibration isolation pads between the motor and the transom when I re-install the motor.

A big thanks to Paul (shipwright), thanks for saving me a lot of work and for teaching me new methods.

That’s what is so great about Lumberjocks, So much talent and so many people who want to share the knowledge.

Thanks for Looking!!

-- John, Suffolk Virgina

2 comments so far

View shipwright's profile


8727 posts in 3913 days

#1 posted 04-30-2017 11:07 PM

You’re welcome John. I hope it works out well for you. It should be a very strong repair.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese!

View changeoffocus's profile


467 posts in 2732 days

#2 posted 05-02-2017 10:40 PM

As usual you have provided an interesting new chapter of your work on “Big Brother”.
Sorry that it required a repair to provide us with a great read and testimonial to Paul’s generous sharing of his experience.
Enjoy the summer.

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