9mm plywood cover with fiberglass

[Jakjit Singh]

I am building my very first open fishing boat (5 feet x 24 feet)with plywood. I have no experiance building a boat. Now my question is can I use a 9mm marine plywood and cover it all with fiberglass?? Do think its too heavy??

[PAR]

What boat are you building and why would you deviate from the plans, particularly with your limited building experience?

If you're designing a boat, you should attempt to understand the loads imposed on the structure, so you can calculate material scantlings. Guessing doesn't work very well.

To directly answer your question about 9 mm plywood on a narrow 24' boat, this seems inadequate, unless the boat is quite lightly loaded. You could compensate with a thick layer of 'glass, but this will add more weight then necessary, especially when compared to plywood in this size range.

[lazeyjack]

Originally Posted by PAR

What boat are you building and why would you deviate from the plans, particularly with your limited building experience?

If you're designing a boat, you should attempt to understand the loads imposed on the structure, so you can calculate material scantlings. Guessing doesn't work very well.

To directly answer your question about 9 mm plywood on a narrow 24' boat, this seems inadequate, unless the boat is quite lightly loaded. You could compensate with a thick layer of 'glass, but this will add more weight then necessary, especially when compared to plywood in this size range.

so funny Paul\, I saw a 39 foot cat here, built of 10mm ply, and the silly bugger was going offshore, this bloke spent 30 mins telling me how light the thing was
I have a theory, if you can put a sledge through a boats side then it should never venture offshore

[Jakjit Singh]

This boat I am building is an open fishing boat with a V bottom and for a fishing trip on the coastal area and not a deep sea fishing, loaded with 4 to 5 people. The actual design plans which I follows is using a 9mm plywood only, but I feel that if I use epoxy alone maybe it will leak.. considering that my place here have no other choice of epoxy, the epoxy I use is the normal epoxy which is to be mixed 1 : 1, so I feel that covering the whole plywood with a fiberglass might end the leak nightmare.... what say you....

[kengrome]

Did you design the boat yourself?

[Jakjit Singh]

No, I took it from the Fishing boat designs: 2. V-bottom boat of plywood construction (Rev.2) from FAO, fisheries Technical Paper 134 Rev. 2.

[kengrome]

Those FAO boats are well engineered, if you build one properly it won't leak and you won't need to worry about covering the boat with epoxy. Just use epoxy to glue all the wood pieces together and you'll be fine.

[Jakjit Singh]

Thanks Kengrome, but the problem is that, this is my first time building such a boat and also first time using epoxy. At my place here we dont have any choice of epoxy, just mixed the epoxy (1:1) and added some thinner with it... Any advise from you???

[kengrome]

Never add thinner to epoxy, it is not paint and should not be used like paint. There's lots of information in this forum and elsewhere online that you can study to learn how to use epoxy and other materials correctly.

Perhaps your first source of advice should be the epoxy manufacturer, don't they provide instructions or guidelines or technical support?

[Jakjit Singh]

Do you suggest to replace the 9mm plywood to a say 6mm plywood...

[kengrome]

ABSOLUTELY NOT !!!

You should build the boat using the specified material thickness even if you cover it with epoxy and fiberglass. Do not use thinner wood.

[PAR]

Thanks Ken, I'm the one that usually catches these. I thought my previous reply would cause the original poster to look over his modifications, but apparently not.

Jakjit, the boat you're building doesn't need epoxy. It was designed to be built using convention methods and no sheathing. It also is intended to be light weight (considering the method and materials) and more importantly easily propelled with rather modest power (hence the nearly 5:1 beam/length ratio)

Do not decrease the dimensions of anything. Adding a sheathing of fabric, set in epoxy will improve waterproofness and abrasion resistance, but little else.

[kengrome]

Adding a sheathing of fabric, set in epoxy will improve waterproofness and abrasion resistance, but little else.

This is absolutely right, thanks for mentioning it Paul.

I had written the same thing in my reply, but then I removed it before posting because I waanted to make my other point clearly -- without including anything extra that might confuse the issue for Jakjit.

[Jakjit Singh]

Thank you guys, boths of you has been a great help. I am now confidence in building my very first fishing boat. Thanks again.

[shilshil]

Hi Jag,

Lots of these type FAO boats in use in our waters. they go out in all conditions and fish well offshore. Offcourse the fishermen know the boat and waters well.
Can post you some photos, if I figure how to post them.

Shilshil