Transom Cracks

[williamtii]

Hello All,

I have some cracking on the transom that I have been trying to fix cosmetically without success. Every year I put on Marine-Tex and shape and sand to form. And every year it cracks again.  This is the worst so far on the port side, followed by other areas:







Should I be worried about any of this structurally? The transom looks solid and strong but it is original and I dont know how many times it has been re-powered. At least once by the poorly sealed holes I have had to clean and re-fill.

Is there a better filler that maybe isn't as rigid as Marine-Tex ? I think a bit of the cracking comes from trailering the boat with the motor trimmed up, putting stress on the top edge. This year I will put the lower unit on at the boat ramp to help with the weight bouncing.

[RickK]

What you're seeing is the part of the liner that covers the transom core. You can keep using MarineTex or even use latex caulking. With your engine tilted up put weight on the lower unit and bounce it while watching the transom for any flexing. If you see flex, it's time to rebuild the transom.

[Enginerd]

You could grind back to fresh glass/wood and fill with a mix of epoxy, cabosil, and long fiber. The reason the marine tex keeps coming out is the crack is expanding more than the marine tex can expand. And/or the marine tex is not bonding well to the weathered cracked glass. The fiber reinforcement will prevent the crack from opening up.

There's a good chance your getting to the point of needing a transom rebuild, as Rick said.  If you're trying to hold off, I'd either fill as described above, or remove the motor and glass over the entire top edge of the transom, extending down onto the transom face. It looks like cracking has begun all along that joint.

[wingnut]

I'd agree with the others that your transom may be approaching the end of its life - just as a word of caution, mine looked similar when I brought it home... Very minimal flex to it, but it was still wet mush inside when I dug it out. Catastrophic transom failure on the water is bad news...

Similar crack:

[CTsalt12]

Strictly curious and I don’t mean to 2nd guess: has anyone ever heard of a catastrophic transom failure on the water or off?  I remember I looked at an older Seacraft being sold by an older gent once, the transom had basically split where it met the gunnels and the guy said he was still using it ! Crazy.   

[theFunsmith]

I have had a transom failure on an early 70s 16' starcraft. Rotten wood insert let go, and the motor came loose under power. Not a fun deal pulling an outboard back to the boat by the steering cable. Luckily it was only a 25hp.

I would drill a test hole ~1/4" in the lower center part of the core material. Ten to one you're going to have water coming out of soggy plywood. At least then you'll know whats in there.

[williamtii]

Thanks guys. Yes I think it's becoming about time but trying to get as much life out of it as possible without major surgery. When the current "98 motor was put on they just filled the old holes with caulk. We have had it about 10yrs and I would guess it was repowered long before that. I removed the caulk plugs, drilled the holes a little bigger and let dry over the winter 2yrs ago. Definitely mushy stuff in there around waterline height.

I do not notice flexing under power but will do the tilt up and bounce test. I dont think the transom would survive another repowering without rebuilding it, but it does seem strong as is.

[RickK]

The original transom fiberglass skin is around a 1/4" so it can hide a bad core for a little while plus adding the liner thickness could seem strong. When I rebuilt my 170 the transom seemed solid but when I started removing the core it was rotten.

[theFunsmith]

Definitely mushy stuff in there around waterline height.

Then you know what the right answer is.