Foam dinghy

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fallguy1000
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Re: Foam dinghy

Post by fallguy1000 »

Netpackrat wrote: Sun May 31, 2020 11:42 pm Perhaps a hybrid construction with plywood bottom panels for puncture resistance, and foam elsewhere?
No. Too heavy.
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jacquesmm
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Re: Foam dinghy

Post by jacquesmm »

Evan_Gatehouse wrote: Sun May 31, 2020 10:19 pm The problem with ultralight foam/glass dinghies is the skin is pretty vulnerable to punctures when you drag it up on rocks etc.
12 oz is as light as I would go - and maybe an extra layer along the keel line if it is a V bottom.

Those sort of davit holders are Weaver - look at pg 13 and 17 for details of connections to hard dinghies. It's just a bolted plate on the dinghy side.
You would have to locally reinforce with an extra layer of glass and certainly use thicker foam for local stiffness - at least 2x the area of the boling plate
https://www.weaverindustries.com/images ... atalog.pdf
Yes, that's the problem with weight in small foam sandwich boats. I agree that 1 layer of 12 oz. is the minimum and that is what I specify for the light version but on my own dinghy, I will have more glass.

Ok for the Weaver davits attachment. They require a HD foam insert.
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jacquesmm
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Re: Foam dinghy

Post by jacquesmm »

fallguy1000 wrote: Mon Jun 01, 2020 12:42 am
Netpackrat wrote: Sun May 31, 2020 11:42 pm Perhaps a hybrid construction with plywood bottom panels for puncture resistance, and foam elsewhere?
No. Too heavy.
You would be surprised. I did the math and a hybrid version weighs almost the same than my light version.
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fallguy1000
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Re: Foam dinghy

Post by fallguy1000 »

It is very easy for me to compare.

I can compare a 6mm ply with 12 oz glass bottom and 6mm ply sides with 6 oz glass each side with the TD3 as specified; all others equal.

Where the foam TD3 may have trouble is I believe it is 6 oz too heavy glass on bottom. I am taking the spec from memory and using 12mm core.

A 6mm ply panel at 20 pound per sheet and 50" wide and 10' long bottom and 12 oz glass both side hand lam is 40 pounds! A 6mm ply panel 30" wide at 10' long with 6 oz glass each side is 20 pounds. The plywood panels are like 60 pounds. I can cut 6 pound with vac to 54 pounds and the panels are smaller, but did not include pram bow or transom or seats or stiffeners.

A 12mm core bottom panel, same glass is 8.7 pounds core and 13.9 pounds glass and resin hand laid and the sides are 5.2 pounds core and 4.2 pounds hand laid. Now, this comparison might be light! So, let's double the glass for semantics. 36 pounds glass and 14 pounds core; still lighter than the vac version of the plywood. If I use vac against the 36 pounds glass and resin, I save 12 pounds to 38 pounds.

I can almost guarantee I can build an 8' version of the TD3 dinghy at 30 pounds. Is it made to sail the 7 seas? No. Would it be strong enough to harbor hop. Yes.

Kind regards. Let me know if you would use 3-4mm ply; you'd almost need to to make it comparable to foam.
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jacquesmm
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Re: Foam dinghy

Post by jacquesmm »

I don't specify 12 oz. on each side for a plywood dinghy of that size. It would be 6 to 12 oz. outside only, up to the WL, not the sides. Nothing inside except for the tabbing.
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fallguy1000
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Re: Foam dinghy

Post by fallguy1000 »

jacquesmm wrote: Wed Jun 03, 2020 2:01 pm I don't specify 12 oz. on each side for a plywood dinghy of that size. It would be 6 to 12 oz. outside only, up to the WL, not the sides. Nothing inside except for the tabbing.
Thanks. I will recalculate later today. Dan
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