Layup of kayak material question

[Thin water]

I have a mold for a 12' kayak. I made a boat in it a few weeks ago using three layers of 1 1/2 oz mat and polyester resin. The top fits like a shoe box. I fiberglass taped the inside, foam filled the ends. I flipped over and filled the little gap between the top and bottom with thickened resin.

The thickness seems fairly close to what "Feels" like it is right, no excessive flex but not a brick either.

The weight seems a little excessive, it ended up being around 65 lbs.

I want to try one with one layer of 1 1/2 oz mat and one layer of 24 oz woven roven. It (the 24 oz woven) is only slightly heavier than a layer of 1 1/2 oz mat when wetted out per a chart I found on this site. If the weights are like the chart says I should be able to get it down to under 50 lbs by eliminating the third layer.

Any suggestions on this layup? What would be a "standard" layup for a boat of this size?

I am also making the plug for a 13 1/2' open kayak. I will use 1 x 2 cyprus rub rails on it to help stiffin the sides and a small deck fore and aft. Will the layup on this boat be similar to the regular decked model?

Thanks,

JIM

[BarendGrobler]

Without doing any calculations; what I see in a similar kayak I have; they used a thinner cloth (don't know the weight in yank-terms, but in propper terms its probably a 100 to 200g/m^2 cloth). One layer of this on either side of a very thin (probably about 2mm) foam core. Very light, very stiff!

[the1much]

watch out for the amount of resin used, that adds alot of your weight , and thta wooven roven takes more then most the charts say, i havent seen the one your talking about. poly resin in roven does alot of sagging.

[JRL]

1 yard of 24oz woven roving will consume less resin than an equal size piece of 1.5oz CSM. I personally have a hard time getting it to wet out %100.

If you use WR over your CSM you will get a healty amount of print through.

Wish I could help you with the layup. But the only thing Ive made that floats are buoys.

[alan white]

I have a mold for a 12' kayak. I made a boat in it a few weeks ago using three layers of 1 1/2 oz mat and polyester resin. The top fits like a shoe box. I fiberglass taped the inside, foam filled the ends. I flipped over and filled the little gap between the top and bottom with thickened resin.

The thickness seems fairly close to what "Feels" like it is right, no excessive flex but not a brick either.

The weight seems a little excessive, it ended up being around 65 lbs.

I want to try one with one layer of 1 1/2 oz mat and one layer of 24 oz woven roven. It (the 24 oz woven) is only slightly heavier than a layer of 1 1/2 oz mat when wetted out per a chart I found on this site. If the weights are like the chart says I should be able to get it down to under 50 lbs by eliminating the third layer.

Any suggestions on this layup? What would be a "standard" layup for a boat of this size?

I am also making the plug for a 13 1/2' open kayak. I will use 1 x 2 cyprus rub rails on it to help stiffin the sides and a small deck fore and aft. Will the layup on this boat be similar to the regular decked model?

Thanks,

JIM

A light and stiff kayak would be best built using cloth exclusively for glass. Whatever you use, stiffness from glass thickness alone is going to weigh a lot.
A 12 ft open boat in glass should come in at no more than 35 lbs if well constructed. In order to keep it light and get stiffmess too, you must either core the hull in places or use Kevlar or both. Tight radius sections are self-stiffening. The gunwale is also a good stiffener. The bottom is the flattest area, so coring the bottom is a good place to start.
A half inch of foam core in a long football shape (the edges sweep up the sides a bit) should be adaquate.
A way to see what kind of glass schedule works best to limit the overall weight woulf be to do a test square of 12" x 12". Then calculate how many square feet make up the entire hull.
Vacuum bagging also keeps weight down by making a smaller amount of resin do more.
It makes no sense to use mat in building a kayak. It has too much room for resin to fill. Cloth uses the least resin. Woven roving can be used selectively for reinforcing bow and stern, but it too can soak up resin.
Keystone-section foam strips makes for light stringers and frames, hardly weighing more than single layer alone. These can also be used to stiffen the hull.

Alan