JEM Watercraft

Got my plans in the mail yesterday
and have a few questions...

1. Regarding the frames--I didn't see them sketched out on the plywood panels in the plans, are the frames just supposed to come from scrap plywood--or is another sheet required? Also, is there a minimum thickness required for the frames (to be more stable during assembly), or should it be about the same as that used on the hull?

2. There are three options listed, which refer to using less thick plywood depending on how much fiberglassing is being done--1/4" (6mm) vs. 3/16" (4mm). I was planning on glassing the entire hull--but I'm not sure if I can find 4mm ply--how much difference will it make on the 15.5 foot Iroquois if I use the 1/4" ply and glass the whole thing? I'm assuming it's a weight issue--how much difference are we talking?

Frames should have a separate drawing. They are temporary and disposable. So use any cheap 1/4" or thicker ply. Partical/press board would even work.

Using 4mm and glassing inside and out would be about the same weight as 1/4" and taping the seams. But glassing inside and out yields a better overall boat in the long-term.

So if I can only find 1/4" ply, should I just tape the seams and not glass the whole due to increased weight, or go ahead with the glassing and live with the weight?

G'day JT,

If building out of 1/4" marine grade ply, I would recommend just taping the seams, inside and out. The fibre-glass will add significant weight.

If you choose this method, I would also recommend several coats of epoxy resin to all surfaces of the ply. it will increase the strength of the ply and protect it well.

As Mick told you ... the saturated wood is stronger...

Take a scrap piece of the wood and epoxy saturate it ( both sides) and let it cure , now take a piece identical in size and width... Break it and then try to break the epoxy saturated one .... see which is stronger.

I can't prove it but it sure seems like the truth ... they say the epoxy saturated wood is 4 times stronger the the plain wood.

Now you can ( if you want to ) fiberglass that wood on both sides and you have a very strong boat but light weight. Plus the epoxy saturation soaks into the wood giving the epoxy for the fiberglass something to bond with and it also protects the wood in case a puncture gets threw the glass's to the wood. Double protection for your boat.

I made one pirogue out of 1/4 , then epoxy saturated the wood ...and only taped the seams , it is still with me and has been used. Some of the boats I have only glassed the outside while others are glassed inside and outside , it just depends on how you want to make it.

One thing... ALL of mine have been epoxy saturated 1st.

Chuck.

jt wrote:So if I can only find 1/4" ply, should I just tape the seams and not glass the whole due to increased weight, or go ahead with the glassing and live with the weight?

Whoops! I didn't communicate my meaning very well.

Ugly 1/4" is ok for THE TEMP FRAMES ONLY!!!

For the hull panels that will be a permanent part of the boat, use the best ply you can find/afford.

Using 4mm ply and glassing inside and out will yeild the about same weight as using 1/4" and taping the seams. You can get lighter by using light-weight options. But I would not recommend that for a first time builder.

Thanks for the replies. I'll look around and see what's available. I know that the big box stores only have the 1/4" ply (oak, birch, or luann), but there's a company in Ft. Worth that has marine ply about twice the cost, but sounds worth it.

Matt,

You're meaning was fine, I understood the temporary nature of the frames meant they could be ugly...(kinda like a few relationships back in the day...temporary and ugly)

Hopefully, we'll get some materials and get started soon...

I called the company in Ft. Worth, but the thinnest they have is 1/4", no 4mm.

Sooo, approximately how much weight would be added by
1) glassing the whole thing inside and out using 1/4" ply

or

2) glassing just the bottom using 1/4" ply

versus just taping the seams?

Also, if using 1/4" ply (and glassing optional) could I use lighter cloth, or would that make a difference?

I'm not trying to shave pounds (it's just my first build), but wasn't sure if we were talking 20 pounds difference or more like 5...

you'll be about 8-12 pounds heavier. Maybe more.