How to mold a bow bumper?

I would appreciate any suggestions for making a bow bumper.

I have made a master out of balsa and cast a plaster mold.

I put some vasaline in the mold as a parting agent.

I filled the mold with silicone sealant. It set on the surface but did not set through after 24 hours.

Should I layer the silicone to let it cure, or just fill the mold and leave it much longer?

Any other suggestions or materials?

Thanks in advance

John Ball
Vancouver Island. BC
IOM Triple Crown (under construction)

I think it will cure if you leave it set long enough. Might take several days.

If you can get the stuff in small quantities in the US, the best stuff I know is a 2-pot urethane rubber.


Try this method - a heck of a lot less cumbersome. It does take at least 48 hours to setup as silicone cures very slowly.

courtesy of us “Multihull Freaks” ;):stuck_out_tongue:

you know that is a realy good idea. i do it somewhat harder. i think i am going to try and do it your way dick. never would have thought of using the cardboard that way:zbeer:

Glad to be able to help out a “monohuller” :smiley:

Cougar, remember that silicone does cure very slowly from the outside in - be patient, Have a couple of beers - maybe more.


well dick
from us guys who are “SINGLE MINDED” :lol: We like when you guys who has along good infromation. what i have been doing was making a balsa plug. then using making tape. and glueing it to posterboard. we make a box and then pour plaster. when that is cured, i pull the balsa plug. then use pam cooking spray and spray the entire mold, and just use silcone. wiat for 3 days ( or a case of beer) and then pull the bumper
i like your way better. and i am going to try it

Another way to speed up the cure time is to put the silicone into the mold, and then insert a foam filler piece so that the silicone thickness is only 1/8 -1/4 inch (3-6 mm) instead of the full thickness of the bumper.

It’s still going to take more than 72 hr to cure, if I recall correctly. But I remember I still had a gooey liquid center after a week without it.

Cougar, I never thought of using Pam as a mold release. I’ll have to give it a try.


I dunno, I just buy a pair of cheap flip-flop sandals of the appropriate color from Walmart, chop out the bumper using a belt sander and glue it on with 3M 5200. But then for free sailing you want a bit “spongier” bumper than an R/C boat, where hitting the side of the pond is supposed to be a rare occurence :slight_smile: I do admit molded ones look better.



If that means you don’t need the case of beer any more, I’ll stake my claim to it now:sly:

Cougar -

Martin is correct - please forward the case of beer to his attention at your earliest… in fact, just go ahead, buy and send him one trust me that mine will arrive at your doorstep any day now ! Like many of my checks - they are in the mail.

:smiley: :wink:

Thank you to all who replied to my question.

My second molding attempt using silicone caulking seems to have worked, after leaving it for three days to cure.

If the silicone turns out to be too fragile in use, then I’ll try to recast using a molding rubber.

Thanks again

I am building the Nimbus MK II and it suggests for the bumper " the foam used for the sole of some inexpensive sandals is an excellent material." I would think that you would glue them together and shape it, and attach it with silcone.