GV 11 materials question

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GV 11 materials question

Post by jnb » Wed May 06, 2020 2:00 pm

Hello all,

I joined this site a few years ago with the intention of building something big but then life interfered and I disappeared after having a kid, moving houses, etc. Finally getting back to it and just purchased plans for a GV 11. Eventually I'd like to build something in the 16-17 foot range to use on Puget Sound, but I think a smaller boat is a little more realistic for me right now and I could use a little practice.

I had a couple questions regarding the GV 11 that I'd love some input on. My intention is to keep it as light as possible so I can car top it if need be. Seems like this should be realistic if built to specs, a little over a hundred pounds. The only option I'm planning on adding is foam under the seats.

However, I noticed the plans do not require the hull to be glassed but some previous builders on here have glassed the outside of the hull. Could anyone give me a rough estimate of how much weight this adds?

The reason I'd like to glass the bottom is because we've got rocky beaches around here and it'll probably get dinged every now and then, especially if I'm not launching with a trailer.

I was thinking if I used okoume, that would keep the weight down a little offset the additional weight used for glassing the bottom.

-James



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Re: GV 11 materials question

Post by Jaysen » Wed May 06, 2020 2:17 pm

Welcome back...

The answer to the "how much weight for glass" is "it depends".
1. What glass are you using?
2. How good are you with resin to glass ratio?

A quick way to think about it, is to take the glass weight and multiply by 2. That is the resin+glass weight per square yard if you are prefect with the resin:glass ratio. Next figure out up much you will use in terms of square yards. Multiply that number by the glass weight.

So if you use 6oz glass and need .8sqyd you wind up with (6x2)x0.8 or approximately 9.6 oz.

Realistically you will be closer to 1.3x resin to glass changing that to (6x3.3)x0.8 or approximately 16oz or 1lb.

You will need more than 0.8yd. I used that number to make it easy to see. You will likely want 12oz glass. on my v12 I think it was close to 15lbs but I'm a resin pig. :)
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Re: GV 11 materials question

Post by terrulian » Wed May 06, 2020 2:32 pm

If you drag your boat on rocks, without glass scratches WILL go through to the bare wood.
It's a trade-off for sure.
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Re: GV 11 materials question

Post by jnb » Wed May 06, 2020 2:55 pm

Thanks for the input.

I was thinking of using 12 oz on the bottom panels and 6 oz on the sides.

I think my glassing skills are somewhere between poor and very poor. I've only ever done smaller repairs on other boats before, so I'll be on the uphill side of the learning curve.

Using some really rough math, I think if I save about 10-15 pounds from the specs on the the plywood and add 15-20 with the glass bottom and 10 boxing in the foam, it will put me somewhere in the 125ish range. I'd consider that on the heavy range of a car topper but still doable for sure.

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Re: GV 11 materials question

Post by Reid » Wed May 06, 2020 3:54 pm

jnb,

In my opinion I would either use one layer of 10 oz woven or two layers of 6 oz woven (gives you a total of 12 oz woven). The woven is easier to fair and will then use less epoxy and fairing compound, thus cutting down on weight. If you are worried about abrasion you could also coat the bottom with graphite powder/epoxy. If it is scratched it is easy to repair.
I think the weight added by the 6 oz or 10 oz would be negligible compared to the overall build.

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Re: GV 11 materials question

Post by Evan_Gatehouse » Wed May 06, 2020 4:20 pm

OK - I would have suggested the GV10 if you were really serious about car topping. The GV10 is a huge 10' dinghy. It regularly accommodated my family (2 adults @ 185/230) + 1 kid (>100 lbs) easily.

Five or six Fijian kids and me - still lots of freeboard though it wasn't going to plane with that load!

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No need to glass the sides. Just epoxy coat and paint if you are using good marine tropical hardwood plywood. You'll save the most if you use a lighter plywood like okume (18-21 lbs for 1/4") versus meranti (27 lbs) x several sheets. If you use douglas fir you'll add more weight because usually you have to add a light layer of glass to prevent checking.

No need to box in the foam with plywood. Light layer of 4 or 6 oz cloth. Keep it away from gasoline spills however.

For the bottom, single layer of 12 oz biaxial inside and out is strongly suggested for planing hulls. Two layers of 6 oz woven won't give the same strength because it's a woven. Fairing compound shouldn't weigh more than 1 lb for the bottom if you peel ply the glass.
designer: FB11/GV10,11,13/ HMD18/
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Re: GV 11 materials question

Post by jnb » Wed May 06, 2020 11:58 pm

Thanks, Evan. For the bottom, do you mean just the bottom panels and plus a couple inches over the joint with the side panels?

I was thinking of an 8 HP engine or something relatively modest. Is the 12 oz biaxial on both sides necessary even if I've got a relatively small, albeit planing, engine?

Hadn't heard of peel ply before, but just did some reading on it, so thanks for that suggestion.

I spent a long time waffling between the the GV10 and the GV11, but we've got some big dudes in my family so I figured I was more likely to wish the boat was a little bigger than a little smaller. Lifting heavy stuff is not a problem for us, but "displacement" is an issue we run into from time to time. The weight is mostly a concern due to the roof rack's limits and what happens once it's up there.

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Re: GV 11 materials question

Post by Evan_Gatehouse » Thu May 07, 2020 10:13 pm

I was thinking of an 8 HP engine or something relatively modest. Is the 12 oz biaxial on both sides necessary even if I've got a relatively small, albeit planing, engine
Yes, because an 8 HP will get 1 or 2 people up to planing speed. And if you're doing 15 or 18 mph the bottom impact forces are significant.

You can stop the biaxial at the chines, no need to lap it up the sides. It's the bottom panels that take the pressure impacts.

With me (250 lbs at the time?) + 15 HP 2 stroke I did >25 knots in my GV10. I can tell you the bottom was feeling the small waves. I routinely drove it that way in light chop.

I once picked up the GV11 prototype on my back while it was upside down and carried it to a car to car top it. It was not easy single handed. With 2 people it was easy. Check your roof rack widths - it's pretty wide
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Re: GV 11 materials question

Post by Evan_Gatehouse » Thu May 07, 2020 10:14 pm

Peel ply will change your life when fiberglassing. Ask anybody who has used it.
designer: FB11/GV10,11,13/ HMD18/
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Re: GV 11 materials question

Post by jnb » Mon May 11, 2020 12:12 am

For the seams and frames, the plans call for 4'' 9oz fiberglass tape. I'm only seeing 6 oz or 12 oz in the store. Is it ok to substitute? If so, better to go bigger or smaller?

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