Foamboat construction

Step 12 P05, one mold and one finished

One finished mold and a twin after it has been fiberglassed and painted with white exterior latex house paint.
I will be glad to reply to comments and questions posted by interested folks who have first thoroughly studied this Instructable.
U. S.

Comments

[michaelhoover]

im curious to know how the boat hull has held up over time. Is there any cracking or denting?

[unclesam]

michaelhoover, the hulls look the same today as they did the day I finished painting them, no dents, no cracking, no flaking of the paint. They have been stored outdoors uncovered year round, bottom side up, exposed to the weather and direct sunlight, Mid-Atlantic U.S. coast. To see more photos in my related Instructables, enter unclesam in the Instructables home page search box, page and scroll to see them all. Uncle Sam

[sdavisrt]

I have a fiberglass boat that was stored with the hull facing up.  The gel coat now looks horrible and I want to paint it with something.  I have sanded the bottom so whatever I used would have a good surface to adhere to.  Does the latex paint hold up ok? This seems like a very economical way to make my boat look better. And I don’t mind if it has to be reapplied now and then.

[minipancho94]

if your gona go the cheap way instead of the better way that unclesam said, i wouldnt go with latex, it can get peeled off by the tape if your painting borders n stuff, also not all latex paints are water proof if any are. you can use latex but your gona need to water proof it.

[whowild]

Please do not use latex, if you can not get your hands on some gel coat then an automotive enamel will work well.  If you're just going to paint the bottom of your boat, a quart would probably do.

[unclesam]

sdavisrt, sanding will really help any coating to adhere. See my other instructables about boat construction and fiberglassing by entering unclesam into the home page search box, page and scroll to see them all. I would use a primer under the latex paint. For the latex paint to be durable in this application, it needs to be premium, it needs to be white with titanium dioxide as its pigment, in order to block sunlight, such as Sears Weatherbeather exterior. If the paint you choose calls for a primer on its label, I would use that primer. A primer provides a stronger bond between the surface and the first coat of paint than does paint alone. On the two long hulls featured in my fiberglassing instructable, I used a sanding primer. It brushes on thick, like a coat of plaster, and fills pockmarks, cracks and the weave of fiberglass cloth. It sands smooth very easily, helps the coats of paint to adhere. The latex paint on those long hulls still looks perfect after over 10 years of direct exposure to the weather, all year long in Mid-Atlantic U.S.
Unclesam

[broham]

I want to use my old 10' jon boat for a mold (outside of boat ). I want to lay glass or kevlar over boat that has been treated with a release and copy about half of it (bow section). Then make a second copy of about half (bow section again) and join the two together, I now have a punt for shallow water work. How would I join the two halves together for the strongest bond?

[unclesam]

Second thought, make one half as you propose, make the second half several inches longer and the added inches slightly larger, nest the two open ends and epoxy the halves together. Before laying up the second half, tape band of cardboard across boat bottom and up sides, several inches wide and as thick as your expected layup. Fiberglass over the boat bottom and the cardboard band. Open end of first half should nest into those enlarged few inches of second half. Overlap should provide plenty of area for adhesive and provide extra strength there. U.S.

[broham]

Hey thanks for your quick follow-up. I'll do as you suggested. I purchased plans for a 16' lapstrake row/power/sail called the "whisp" several years ago and never built it. I'm planning to make it out of foam and laminating it. Just started the learning curve building and working with foam. Thanks again for your help...bill

[unclesam]

Best would be to incorporate overlap at the joint, but I cannot figure out an easy way to do that without creating a bulge on the outside of the bottom of the boat. Next best would be to make butt joint and put glass and epoxy patch over it that overlapped several inches onto each half of the boat. It would make a small bump, but it could be feathered. Once crack had been covered on inside of the boat with several layers of glass, I would putty any crack on the outside between the two halves with epoxy filled with very short strands snipped from scrap fiberglass cloth, add at least one layer of glass over the underside of the crack in the boat. If you are worried about strength, you could epoxy strips of thin plywood over the butt joint on inside of the boat, then glass over it. U.S.

[Jerobajas]

For a smooth, yet stronger butt joint, insert rigid discs called "biscuits" , wooden dowels or even carbon fiber spars buried 50% into each of the sections being joined. The discs, or other planar form such as battens should be placed in plane within the pieces' joint. A ribbed structure, sort of like a wing layed over equal lengths of each section would be a very strong way to reinforce a two-piece boat, if enough ribs are used, and enough epoxy and glass roving goes on top of them. I've seen a nice design which made use of the interior volume of the "wing" in the bottom of the boat by placing waterproof hatchways through the fiberglass into the cells between the ribs, for handy storage of gear. This design was made to stow nested, and be joined only during use; a sort of "collapsible boat", and though I dislike that juxtaposition of words, the virtues of the concept are undeniable for cruising yacht tenders or cartop use.