Whitehall questions.

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tsmitherman
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Whitehall questions.

Postby tsmitherman » Sat Jan 22, 2011 5:07 pm

I've been looking at the Whitehall as a possible project for some clear cypress that I have in the shop, and would like some opinions/suggestions regarding the following:

Based on the description for the fiberglass kit for this boat, only the outside is fiberglassed. If I glassed the inside and out, could I use thinner strips than the 1/2" thick strips that are called for? How thin can I go?

(In 2007 Tom Hoffman posted on this forum that he'd built one using 3/8" strips, but did not specify if he glassed the inside. I don't know if he is still active on the forum.)

As drawn, the Whitehall is 16' 11". I would probably shorten it by 5 or 10%.

I would like to make it as light as possible without comprimising the strength of the hull.

Any thoughts?????????
Tom
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Travel Log at www.tomstug.blogspot.com

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Lowka53
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Re: Whitehall questions.

Postby Lowka53 » Sat Jan 22, 2011 6:16 pm

:roll: your can always make your wood longer by scafing them together cypress is pretty strong wood and hard to come by these days but a very good boat wood
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tsmitherman
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Re: Whitehall questions.

Postby tsmitherman » Sun Jan 23, 2011 6:21 am

No problem with the length of the strips - my concern is how thin can I make the hull and maintain sufficient strength if I glass inside and out.
Tom
------------------------------
Knot-So-Fast (A stretched Bo-Jest design)
Travel Log at www.tomstug.blogspot.com

"It's amazing what one can do when one doesn't know what one can't do." - Garfield

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kens
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Re: Whitehall questions.

Postby kens » Sun Jan 23, 2011 7:33 am

To keep the boat light as possible, do away with the fiberglass.
Fiberglass is heavier than wood. Your proposal is counterproductive since you say trim away light wood for heavier fiberglass.

If it was me trying to do a project like that, I would build it to specs with the cypress, and glass the outside with a very light cloth like 4oz or surfboard cloth. no fabric on the inside, only encapsulate insides.
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galamb
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Re: Whitehall questions.

Postby galamb » Sun Jan 23, 2011 8:53 am

I agree with Kens on this one.

I have some numbers for red cedar that may help you make your decision.

1/2" red cedar strips (8% moisture content) weigh 14.6 ounces per square foot and have a "pounds to failure" rating of 770 psi. So if your plans called for 1/2" strips whatever composite you choose would have to at least meet that 770 rating.

A 3/8" red cedar strip with "glass" on one or both sides would weigh as follows:

1 layer of 4oz cloth = 12.7oz/sqft - failure at 250 psi

2 layers of 4oz cloth (one each side) = 14.1oz/sqft - failure at 675 psi

1 layer of 6oz cloth = 13.1oz/sqft - failure at 298 psi

2 layers of 6oz cloth (one each side) = 15.4oz/sqft - failure at 823 psi

In this case you would have to go with the 2 layers of 6oz to meet/exceed the strength of the 1/2" strips alone and it would weigh 6% more (about 5 pounds heavier on a 15 footer).

Then add in the cost of the cloth, plus the extra epoxy to to wet it out/fill it and you quickly see that using the thicker strips is both lighter and more economical.

And while the above numbers are for cedar, you can safely assume that other species would be somewhat similar.

(numbers were borrowed from research/testing done by Gougeon Brothers/West System - credit is due to them).

The only time it appears "feasable" to use a thinner strip with glass is if you have to make such severe bends that the thicker strip would not readily conform to your mold.
Graham

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kens
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Re: Whitehall questions.

Postby kens » Sun Jan 23, 2011 10:51 am

does anyone realize just how heavy fiberglass is?
If you look up specific gravity of fiberglass, wood, and cement, you find that f'glass compares with cement :shock:
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tsmitherman
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Re: Whitehall questions.

Postby tsmitherman » Mon Jan 24, 2011 7:16 am

Thanks Ken and Graham.

That's what I love about this forum - it keeps my thought process from running off the road into the ditch.

The stated weight of the Whitehall is 350 lbs. After a little math, I think this probably a high estimate. With cypress at 32-34 lb/cf, it seems that the boat should be significantly lighter than that, even using the 1/2" strips.

So ... as is often the case, maybe I was worrying about something that I didn't neet to worry about.
Tom
------------------------------
Knot-So-Fast (A stretched Bo-Jest design)
Travel Log at www.tomstug.blogspot.com

"It's amazing what one can do when one doesn't know what one can't do." - Garfield

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kens
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Re: Whitehall questions.

Postby kens » Mon Jan 24, 2011 2:55 pm

I like the cypress I used on my build. It is strong and light. accepts epoxy like water to a sponge. i layed up a laminate of cypress for my engine stringers.
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Bill Edmundson
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Re: Whitehall questions.

Postby Bill Edmundson » Mon Jan 24, 2011 7:26 pm

Tom

My wood strip canoe is cedar 1/8" thick. 6 oz. cloth inside and out. It weighs in at 65# for a 17' boat.

Bill
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