Moulding engine well plug inside well - technology?

[slawosz]

Hi,
I would like to upgrade my outboard well plug. To do this, I need to create a mould from existing plug, or use well itself as plug. I am thinking about using normal CSM, this resin: Lloyd's approved Polyester Resin (including catalyst) Crystic 2-446 PA
I don't plan to use gelcoat, I will just sand element afterwards, as well I will surface tissue for better finish. However, what should I use as release agent? What else should I remember?

 

[William_H]

What no replies? I presume you mean a removable plug for the outboard well hole. If you have a plug the easiest thing is to make a female mold from the existing plug. Release agents can be purpose made paint on stuff. Onto this you can add wax like floor wax. However cling wrap and plastic throw away carrier bag plastic can also be OK.
The thing is to be careful of the shape of the mold to permit the old plug to be removed. So taper sides are better than square sides. Make the mold from CSM and polyester resin. You often need structure around the outside of the mold to keep it's shape as GRP will be thin and floppy. Use steel ali wood or similar. Once you have a female mold you can improve the surface with filler etc to get the right finish. Then make the new plug out of polyester and CSM. Fortunately when it is a one off you can destroy the mold to get the plug out. I would say you would be foolish not to do a gel coat first. ie ordinary resin with a pigment if you want that is allowed to go semi hard (gel) before you apply the CSM and resin.
The whole thing will be more difficult if you don't have decent old plug to copy but then why would you make a new one? If you have to, make a cover over the bottom to the shape of the hull. Then line the well and bottom cover with cling wrap and possibly card board etc to make a clearance size and lay up the plug in situ. (all while standing on your head). If it were me I would plug up the hole permanently and fit a transom bracket. But my sailing is perhaps different to yours. (haven't had a motor on for some years. ol'will

 

[Ian_Edwards]

You could use a sheet of hardboard, covered heavyweight builders polythene, cargo strapped the outside of the hull to give a fair shape to the under side to the plug.
If you can then fair around the inside edge with some modeling clay/ plasticine and coat with release agent, Carnauba Wax or similar, and then carefully lay in some glass and polyester resin, preferably using some woven mat, rather than CSM, because, it will conform mare easily to the shape of the edges. When the resin has hardened, if you remove the hardbord, you should be able to push the shape the plug up. This will give you a good start for the shape and curvature of the base of the plug.
You need to be care full that you don't get resin on bits of the trunking that haven't been liberally coated with release agent. The plasticine pleas off and you then fill, grind, sand and shape it as required.
When I did this with a Jaguar 21 some years ago ( the boat didn't have plug for the outboard well when I bought it). I reinforced the basic moulding with 10mm marine ply bedded in on a micro sphere polyester mix, and then after trimming up I painted it with 2 pack polyurethane paint, mainly because I had some in stock.
I held in place with some 1/4 turn tabs, because it got pushed up when sailing, and you might want to tie lanyard to it, as a safety line, it might drop though the hole, if the diagonal is greater than the length of one side.

 

[V1701]

I don't know if it's of any use but last time I did a some fibreglass filling I used greaseproof/waxed paper then peeled it off afterwards, the benefits being that I was better able to press it all in to the gaps and it needed less work finishing...