Boat question- Filling old mount holes in transom

mram, Jan 4, 4:40am
Hi, am wanting to repower my fathers old plylite compass 5m from mercury power to OMC V4 and was wondering what the best way to fill in the old 1/2 inch holes was? Bog and gelcoat? any tips? also have to move the bilge bowl drain due to wider footprint(about 5/8) Much appreciated

gammelvind, Jan 4, 4:47am
The easiest way that I have found is a great product from Dinitrol called Fibrestar. Use it just like bog but it is more like chopped strand matting and resin in a can. Strong, flexible, waterproof and can be finished off very nicely. Had a fibreglass dingy with a 30cm crack length wise along the curve of the hull. Ground out the crack bogged it with this stuff, when sanded off the finished result flexed as good as the orginal boat.

grangies, Jan 4, 5:18am
Yes. As gammelvind has said. I use a similar thing called USC Pro-Glas, but it only comes in a 4.7kg tin, which would be far too much for what you need. Dinotrol may come in smaller packages.

The beauty of the fibre-resin fillers is they don't have to be painted over if you're no too fussy.

If you are going to paint it, you don't need gelcoat. Use a 2 pot or a 1 pot marine enamel.

Gelcoat is only used on boats, because it allows the factory to form the boat and paint it all in one step. As in the finish is complete when it is released from the mould.

The big fancy super yachts etc are filled, faired, and spray painted in a 2 pot system.

Trust me, gel coat is a pain in the ass for touch ups.

gammelvind, Jan 4, 5:32am
The dinitrol Fibrestar is a 1.5kg can, or there abouts.

mram, Jan 4, 5:49am
Thanks gammelvind and grangies, Im glad to not use gelcoat!

bwg11, Jan 4, 6:10am
I may be a bit old fashion here, but I would use wooden dowel (1/2" and 5/8") slightly shorter than the holes Secure with 2-pot marine glue. When dry, finish with a marine filler. I would fill the well drain hole and finish completely, then re-drill in the required new position using new skin fittings.

gammelvind, Jan 4, 6:40am
Nothing at all wrong with this technique, but the products we have been talking about do the same job but in one go. Fills hole, glues itself in place and is a marine filler in one go, as well set in 15mins.

lookoutas, Jan 4, 8:08am
Hang on, these holes are through a transom, so I'm picking it will be about 2" thick, and made up of a wooden core sandwiched between glass. If this is so then bwg gave the best method of attack.
Using a marine filler would knit into the glass more effectively and ensure a waterproof seal. You don't want any water getting through to the wood.

I would use proper resin & chopped strand to effect the final plug. Even counter sink the hole a fraction and feather it out to a good 2" circle.

The glass impregnated bog is a good product and quick to use, but no-where near as good as resin.

kazbanz, Mar 25, 12:16am
Without question I'd say THIS ^^^^^^ is the best approach. especially if the dowel can be same material as original timber.