Transom Flatness out of Tolerance

[Boatpuller]

I am disgusted with myself, once again. I clamped the heck out of my transom when installing the new wood and now the outer skin is outside the flatness tolerance. It appears to be right at 3/32" in the middle of the keyhole. See attached photo. Any tips on what I should do to fix it? Sand off the gel coat and add a layer of fiberglass, then sand flat and re-gelcoat?

If I don't learn the hard way I learn nothing at all it seems...

 

[AShipShow]

how long is your straight edge? The Mercruiser specs say it only needs to be within that spec where the transom assembly bolts together? so your straight edge should only be spanning your keyhole plus maybe 5 inches or so past on each side. Only saying this because maybe your lucky and measuring too long of a surface.

 

[Boatpuller]

I believe this was a 24" straight edge / carpenter's square. There is a swim platform of sorts that sticks out above the keyhole (see attached) that is molded into the hull - very little clearance between the top of the drive and hull. The 24" straight edge goes all the way past the bottom of the hull. The distance between the bottom of the hull and the bottom of the keyhole is only about 4".

 

[alldodge]

Does the other side have the same gap?
How about horizontal?
Is the thickness all around within 2 to 2 1/4?

 

[Scott Danforth]

Worse case, a bit of fairing and gell

 

[mickyryan]

just grind and flatten to rest then spray your gel coat or level it with filler and sand and paint , just be sure you constantly checking with strait edge so you don't over sand your repair

 

[Boatpuller]

Thanks all! Gap is not quite as bad on the other side. It might actually be in tolerance. Thickness is currently 1 7/8” but I haven’t skinned or tabbed in transom yet. I clamped the heck out of it in order to stay close to the original thickness (which was 1 7/8) which was probably not necessary. Would I just use glass and resin as filler then?

 

[alldodge]

Could be the reason your transom had issues to begin with is because the transom was not flat from the manufacture. You could use resin and glass but might need to grind away the gel to bond. Maybe Woodonglass has a better idea. I would lean to use a few more layers og gel and sand flat

 

[Woodonglass]

I'd grind it a bit and then mix up some structural PB ( Resin, Cabosil and 1/2" CSM fibers) . use a WIDE spreader and spread it smooth couple hours later use a R/O sander with 60 grit and sand her smooth & Flat.

 

[mickyryan]

you got plenty of room then , i usually go max thickness, as long as i can get bolts on and have thread showing after some worry the splines wont line up as well, i find that hard to believe and i always look and they are bottomed out in the coupling so im pleased.

 

[Boatpuller]

Excellent! Thanks all! I will post pictures of how it turns out!