Very Small Boat Project Question

[Rich M]

I recently designed an 8 ft pram style duck boat (my 4th design - think I'm going to stop here with the duck boats). 7'-10" long, 44" wide and 14" deep. The sides are 6 inches high. The top deck rounds from side to side & from front to back - 24x48 inch cockpit. Two bulkhead type supports in bow area containing 2 pound foam and supports running along the sides of the cockpit from the bulkheads in the front to the transom. 2 foam boxes in the transom. Would like to use around 3 CF of foam in the 4 foam boxes (180# floatation - exceeds USCG requirements) - it is light enough and a little extra does not hurt.

I did a glass over plywood boat and it is too heavy for my 65 yr old father to lug around by himself. I'd like to try making 2 lighter weight ones out of fiberglass with only a piece of 1/4 inch Luan in the flat bottom/floor to provide rigidity for stepping in and out of on...

I've been reading some things on strengths/compresability/etc... and it is all greek to me. I am trying to learn as I have a 14 ft flats fishing boat I'm wanting to build. That's a future project - this one is a baby step.

The boats are for hunting in calm water waist deep or shallower. We usually pull our little boats up on shore to hunt out of - sometimes do a "layout hunt" where they are actually floating.

Can someone give me an opinion on the following laminate schedules - overkill / underkill / possibly might work well?

(Will make a simple female mold and use Vinyl Ester Resin. I'm also not to worried about having a smooth finish - rough is good for a duck boat.)

1. Hull 12 oz biax (45/45) - 3/4 oz mat - 1/4 inch plywood core on bottom / 6 inch 17 oz biax "tape" on sides of the hull - 1 & 1/2 oz mat
Top Deck 3/4 oz mat - 12 oz biax - 3/4 oz mat

2. Hull 3/4 oz mat - 18 oz WR - 3/4 oz mat - 1/4 inch plywood core on bottom/additional 6 inch 18 oz WR "tape" on sides of the hull - 3/4 oz mat
Top Deck 3/4 oz mat - 18 oz WR - 3/4 oz mat

[JEM]

a lot depends on your hull shape, chines, speed you want to move it at, etc. But what you listed sounds like overkill.

[Rich M]

Thanks, JEM.

The boat has a flat bottom and nothing really for chines - the 6 inch high sides have a 4 inch "flare" at the transom and twist to "straight-up" for the front 3 feet of the boat. The boat is originally a "2 sheet skiff". The load is about 250 - 275 pound and drafts in the range of 4 inches under such load.

Overkill? You don't know how happy I am to hear that. I was afraid someone was going to tell me to beef it up more to obtain a specific hull thickness for the sides and top deck.

I reduced the scope a little on the sides and deck. Thinking along these lines now. So much simpler for a simple little boat... Thank you.

Hull 12 oz biax (45/45) - 3/4 oz mat - 1/4 inch plywood core on bottom - 3/4 oz mat

Top Deck 3/4 oz mat - 12 oz boat cloth

[JEM]

Do you have a link to the picture of this boat or something similar? I can pretty much see it in my head but images work a lot better.

Biax is great for distributing loads of power boat. This boat you're building sounds like a trolling motor or paddle power type craft.

Matting is typically for puncturing resistence for soft cores like foam, or adding bulk and stiffness to solid core FRP (that means the hull skin that is made of layers of glass and resin...no core like foam or wood).

If you're using a wood core, I'd say you don't need matting and you're just wasting resin and adding weight. Maybe someone else will point out something I'm not thinking of but it's really not needed for a wood core boat.

I'd say the biggest concern you have is oil canning. You could address that in easier ways without all the extra cloth and resin. Save you some money and boat weight too.

This next part is just assuming you have a flat bottom: With the time you're spending looking to add biax and mat, you'd be better off just going with a little thicker plywood and adding one chine down the middle. This will prevent oil canning, build faster than adding all the matting, and probably end up lighter.

Even going with 1/4" on the bottom and glassing both side with woven 9-10 ounce will give you a very stiff hull.

I design canoes, kayaks, and some small power boats for amateur boat builders. E-mail me and we can fine tune your boat. I've been tinkering with a small duck boat type design. It would be a small and fun project. Translation: I'd do it cheap or even free with some loose agreements. ;)

[gesdim]

Hi,
see http://gaboats.com/boats/ ,
regards

[John ilett]

Being a timber boat epoxy resins should be used which rules out using chop mat as the binders holding the mat together will not disolve well with epoxy.

Also if the hull can be formed from flat sheet then why use a mould at all?

[gonzo]

I have a lot of flat bottom boats about that size with 1/4" ply and no glass. Two 1" 1/2" runners stiffen the bottom and prevent abrasion. Also a frame in the middle.