Note that the weigth of fibreglass and resin together is 96 lb per cubic
foot (Skeen's Elelments of Yacht Design, 30% fibregalss, 70% resin), and
a 1/4" thick layer is 2 lb per square foot. That makes 1/8" layer 1 lb
per square foot, and 1/16" layer half a pound per square foot. I don't
know how thick the various weights of cloth are, Perhaps you could find out.
The cloth has to be more than filled out to it's thickness with resin to
cover the thread and have a smooth hull. There's also the matter of getting
enough glass and resin on the fir plywood to keep it from developing little
surface cracks (checking) which it does from chages in temp and humidity.
I don't know how much is needed, Storing the boat in the shade is said to
help.

I don't know if you've started to build but meranti (luan) plywood is
cheap, rot resistant, and does not check. I assume because you are using
lumberyard plywood, as I do, that you are interested in a cheap boat. I've
built in lauan and virola (not rot resistant) and just painted. I've also
fished from cheap painted (fir and spruce?) plywood punts. You can't get
spruce plywood any more as far as I know.

Dave Allyn ) writes:
I am building a S&G canoe. I am going to use fiberglass cloth on the
entire outside for extra strength, and to prevent any checking in the
plywood. I'm useing 1/4" BCx plywood.

What weight of cloth would I want to use for this aplication? And the
next question, how would I decide that on future projects? Is there a
general rule of thumb for weight?

One last question, I know I need to tape the inside and outside with
fiberglass tape on the seams, but If I cover the whole outside with
cloth, do I still need the tape on the outside of the seams?

Thanks,

dave


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William R. Watt ) writes:

I don't know if you've started to build but meranti (luan) plywood is
cheap, rot resistant, and does not check. I assume because you are using
lumberyard plywood, as I do, that you are interested in a cheap boat. I've
built in lauan and virola (not rot resistant) and just painted. I've also
fished from cheap painted (fir and spruce?) plywood punts. You can't get
spruce plywood any more as far as I know.

I should also note that when I weighed sheets of 1/4" plywood, fir was 22
lb, lauan (meranti) 17, and virola 8.5 lb. Lauan and virola are metric and
actually 1/5". I don't recommend virola becase I don't think the boat will
last long. I have used it for the light weight and because it bends to a
tigher curve than the others.

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William R. Watt wrote:
Note that the weigth of fibreglass and resin together is 96 lb per cubic
foot (Skeen's Elelments of Yacht Design, 30% fibregalss, 70% resin), and
a 1/4" thick layer is 2 lb per square foot. That makes 1/8" layer 1 lb
per square foot, and 1/16" layer half a pound per square foot.
snip

The above applies ONLY to polyester, mat and roving.

It definitely does not apply to knitted glass and epoxy where the
glass/resin ration is about 50/50.

Also, epoxy/knitted glass laminates are much thinner and lighter weight
than polyester/mat/roving for equal strength.

HTH

Lew

Lew Hodgett ) writes:

The above applies ONLY to polyester, mat and roving.

It definitely does not apply to knitted glass and epoxy where the
glass/resin ration is about 50/50.

The above applies ONLY to vacuum bagging. 70% resin is optimistic for a home
builder filling weave by hand.


Also, epoxy/knitted glass laminates are much thinner and lighter weight
than polyester/mat/roving for equal strength.

This is NOT a structural application. It's canoe hull sheathing, abraision
resistance and fir ply check checking.

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William R. Watt wrote:


The above applies ONLY to vacuum bagging. 70% resin is optimistic for a home
builder filling weave by hand.

Rubbish.

According to the total material invoices for the 55ft hull I built, was
able to achieve about a 50/50 wet out using hand layup techniques.

BTW, "hand layup techniques" is just another way of saying a lot of hard
workG.


This is NOT a structural application. It's canoe hull sheathing, abraision
resistance and fir ply check checking.

All the more reason to have a high strength, low weight, high strength
laminate that cloth and epoxy provide.

Lew

On Fri, 18 Feb 2005 14:25:05 GMT, Brian Nystrom
wrote:

Dave Allyn wrote:

For information like this, there are better places for you to ask than
here. I suggest posting on the kayak building forum at kayakforum.com.

I'll check it out. Thanks!

I am building a S&G canoe. I am going to use fiberglass cloth on the
entire outside for extra strength, and to prevent any checking in the
plywood. I'm useing 1/4" BCx plywood.

What weight of cloth would I want to use for this aplication? And the
next question, how would I decide that on future projects? Is there a
general rule of thumb for weight?

Most canoe and kayak builders use 6 oz. cloth, typically one layer over
the entire outside of the hull and often a second layer over just the
high wear "football" area on the bottom. Another common and lighter
alternative is 4 oz. cloth.

Is there a disadvantage for the 4oz? not over the chines or the
bottom, but over the rest of the sides?

One last question, I know I need to tape the inside and outside with
fiberglass tape on the seams, but If I cover the whole outside with
cloth, do I still need the tape on the outside of the seams?

No it's not necessary, but extra wear protection on the chines is a good
idea. The outside should be completely glassed for durability. How much
glass/tape you use on the outside depends on how rugged you want the
boat to be.

Ah.. okay.




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On 18 Feb 2005 15:19:38 GMT, (William R.
Watt) wrote:
I don't know if you've started to build but meranti (luan) plywood is
cheap, rot resistant, and does not check. I assume because you are using
lumberyard plywood, as I do, that you are interested in a cheap boat. I've
built in lauan and virola (not rot resistant) and just painted. I've also
fished from cheap painted (fir and spruce?) plywood punts. You can't get
spruce plywood any more as far as I know.

I almost picked up the luan, mainly for the lighter weight, but the
interior glue threw me. My understanding was I needed to have
exterior glue or the resin could (and probably would) delaminate the
layers. Is that not true? my lumber yard does not carry exterior
glued luan in 1/4" (actually, 5mm)




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On Fri, 18 Feb 2005 02:17:01 +0000, boatbuilder.org
wrote:
It is a good idea to double up the glass on all joints. If you are not
after a clear finish then Dynel is a good choice on the exterior over
the glass tape on the joints. The Dynel will give you better abrasion
resistance and will work better to stop the checking in the plywood.

After reading here, I will definatly double up the joints and the
bottom. Is there much of a cost differance for the Dynel vs. the
fiberglass? Also, can I mix and match? Maybe Dynel on the bottom
with glass on the sides? or do they not wet out the same?

dave


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On Fri, 18 Feb 2005 08:11:18 +0800, OldNick
wrote:
A _rough_ rule of thumb is that if you use full thickness of ply as
designed, and only want this to stop checking and help keep the wood
dry, then use a really light cloth, but reinforce all corners, as
that's where most abrasion is. Also two layers on the bottom. If you
use thinner ply, then build up with cloth until the boat weighs the
same as it would have in ply (reasonably well-laid glass cloth will
take up its own weight in resin, roughly), and you will probably have
a stronger boat.

So, probably tape chines, inside and out, cover entire boat again
with like a 4 ounce glass and then throw a second layer of 6oz, or a
synthetic, on the bottom, and maybe wrap it a couple of inches up the
sides.

Otherwise, talk to the canoe's designer. Always a good idea.

Will do.

One last question, I know I need to tape the inside and outside with
fiberglass tape on the seams, but If I cover the whole outside with
cloth, do I still need the tape on the outside of the seams?

Unless you can cover the whole boat with cloth before you move it from
the building jig, then yes. It's literally what holds the whole boat
together.

I don't have a building jig on this design. It is a simple canoe with
only two "corners"--One chine in the middle of the side, and then a
chine where it hits the bottom. Not sure if that would be considered
one chine or two, but either way it is a simple design.


dave


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On Sat, 19 Feb 2005 13:06:47 -0600, Dave Allyn
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

So, probably tape chines, inside and out, cover entire boat again
with like a 4 ounce glass and then throw a second layer of 6oz, or a
synthetic, on the bottom, and maybe wrap it a couple of inches up the
sides.

The second layer at 6 0z may be only 4? Watch the weight. You have to
carry this thing. Looking at the canoe as a 2' 6" half tube 5 yards
long, 10 oz of glass + resin = 28 lbs!

A lot depends on your usage. If you are goping to simply work open
water with the occasional beach landing, then leave it at 1 layer. If
you are going to be really bashing it about, go for 2 layers.

The one that interested me was Syntex, where they showed 2.8 oz cloth
holding up better than 6oz of glass. But I bet it's $$$$. And they
said it was a bitch to cut.

I don't have a building jig on this design. It is a simple canoe with
only two "corners"--One chine in the middle of the side, and then a
chine where it hits the bottom. Not sure if that would be considered
one chine or two, but either way it is a simple design.

Ok. Make sure the boat is very straight and true before you tape the
outside seams particularly. That is probably my point.