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Old Nov 11, 2011, 04:55 PM
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Homemade silicone Marblehead bowbumpers

Hi all

Has anyone made these and can I have some instruction please?

I have access to silicone material at work ( Otoform) but looks too soft to last.

Or do I just keep making new ones from it?

Any help gratefully received .

Regards

Arhtur G
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Old Nov 11, 2011, 04:59 PM
Useful Idiot
Asturias, Spain
Joined Mar 2001
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Foam flip flops can usually be cut to shape and one old pair should provide enough for many years of sailing.
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Old Nov 11, 2011, 05:06 PM
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Tnx. That was quick. I'll give it a try!!

But to answer my question??

Regards

art.
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Old Nov 11, 2011, 05:45 PM
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Asturias, Spain
Joined Mar 2001
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Silicone takes a fair bit of time to cure for something the thickness of a bumper. But go ahead and make a plaster mould from the current one and keep one or two in reserve. That Otoform seems a bit pricy compared with the normal caulking silicone that most use. However being two part, its curing time is much less, and unless your into naval warefare in your M, it's worth a try testing its durability. Usually most carve a bow block from balsa and use that to make the plaster of Paris mould
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Old Nov 11, 2011, 09:21 PM
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USA, LA, Mandeville
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I have used a 2 part silicone to mold an IOM bumper, and it works well. I made a plug that fit the hull, and poured a two part urethane moulding compound over it and let cure. Then pulled the plug out and poured 2 part silicone, with a colorant added, into it. A few hours later, pulled the bumper out. I used 3M 5200 to glue to bow.

I got both moulding compounds from http://smooth-on.com.

I even made a mold of the bow of one boat, with a bumper "plug" attached to it. Then removed the plug, slipped the mold back onto the hull, and poured 2 part silicone into an opening in the top. Once cured, I had a molded-in-place bow bumper!

You HAVE to use a non-silicone based material for the mold, or the new silicone will bond to the mold and you will have a disaster. Silicone will not stick to urethane and vice versa.
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Old Nov 12, 2011, 10:06 AM
Guz
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Tempe, AZ
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How I did it.

I used double sided tape and taped on a big piece of balsa to the bow. Then I shaped the balsa with a plane and sandpaper. Removed the balsa block and sealed it with epoxy, then painted it.

From there I mounted the balsa on a piece of plexiglass. Then I coated the balsa and plexiglass with Vaseline. Mixed up some plaster of paris (rather soup'y) and poured it a container. Then I pressed the balsa/plexi into the plaster and let cure over night. Popped out the balsa/plexi.

Then I coated the plaster mold with Vaseline, and then filled with black silicone from the hardware store. Using the plexiglass to scrape it smoth to the top of the plaster mold. Again, let cure overnight. I would just poke at the silicone with my finger to see if it was "solid'. You can tell because it feels 'squishy' if it's not. If it isn't, just wet a toothpick with water and poke it into the silicone a couple of times and wait another day. My silicone cures from the outside to inside.

When it's 'solid' pull out of mold. As time goes on, it gets harder.

My silicone bumper looks just like the plug

But the important thing is to use a liberal amount of Vaseline in the mold! If you don't, it's a pain getting the silicone out of the mold.

I hind sight, had I known about using old 'flip-flops', I would have gone down that route.
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