New transom installed but outside of transom is not flat

[78 Thompson]

PBed new transom wood in, but now outside of transom is not flat. Looks like about .100 almost an 1/8 inch, in middle of keyhole going vertical.
Now what, do I have to grind all the gel coat off and fill with fiberglass, then new gel coat.

 

[Baylinerchuck]

The Mercruiser install manual wants no more than 1/16” variance around the keyhole on the outside. Mine was fairly significant, yours is close. Roughing up the area a little and faring with some gelcoat would most likely bring you into spec. If you choose to use a faring compound you’ll want to topcoat with gelcoat. Just make sure it’s something made for below the water line.

 

[78 Thompson]

The Mercruiser install manual wants no more than 1/16” variance around the keyhole on the outside. Mine was fairly significant, yours is close. Roughing up the area a little and faring with some gelcoat would most likely bring you into spec. If you choose to use a faring compound you’ll want to topcoat with gelcoat. Just make sure it’s something made for below the water line.

Ok thanks,
Was that on your Chaparral rebuild? I will have to check out how you did it.

 

[Baylinerchuck]

Ok thanks,
Was that on your Chaparral rebuild? I will have to check out how you did it.

Yes it was. My transom was much more out of spec. I had to sand down my gel to rough it up. I mixed a faring compound using polyester resin, cabosil, and phonelic micro balloons with surfacing wax. Once I fared the area out, I applied more gel coat and sanded out. I most likely bowed mine in when I applied the clamps in replacing the transom core. But like anything on a boat, it can be fixed with time and a little money.

 

[Grub54891]

Mine was like that also. I applied glass on the outer transom then faired as minimal as possible. Used a long straightedge to make sure it was flat as flat. The only worry I had was if the motor would line up properly, but it was perfect. Only had to tweak the mounts a touch. I had rebuilt all the stringers before hand so as much measuring and angles I had to deal with it came out well.

 

[ZippyDoodah2]

Just make sure you're not overcoating with gelcoat. Thick gelcoat is brittle. Cracks and crumbles. No more then 14mils