Cold Molding Instead of Plywood Sheeting

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mrintense
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Cold Molding Instead of Plywood Sheeting

Post by mrintense »

Perhaps this has been answered in the past. The Vera Cruise is defined as using plywood sheeting for the hull. Looking at the photos by various builders shows this as the method used in those boats. However, I like the idea of cold molded more than the idea of using plywood sheeting. It just seems to be a better way (and stronger).

The battens on the front of the Vera Cruise seem quite far apart. I am wondering if it is possible (or advisable) to substitute cold molding for plywood sheeting. Since I don't have my plans yet, it may be that this is answered somewhere in those plans. Unfortunately, several medical issues with my family have held up purchasing said plans. Hopefully by the end of the summer.

Anyway, I am continuing to do research on the process. I would appreciate any input on this. Thanks in advance.
Carl

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DaveLott
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Re: Cold Molding Instead of Plywood Sheeting

Post by DaveLott »

Carl - I reckon you could change the boat from stressed plywood to cold molding. You will need to add more battens. You will then add 3-4 layers of wood to the battens. The boat will weigh more and may influence its performance. If you like the look of a mahogany side, you might consider veneering over the plywood hull. This would give you the same look but not appreciably add to the weight. Just a thought

dave
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mrintense
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Re: Cold Molding Instead of Plywood Sheeting

Post by mrintense »

DaveLott wrote:Carl - I reckon you could change the boat from stressed plywood to cold molding. You will need to add more battens. You will then add 3-4 layers of wood to the battens. The boat will weigh more and may influence its performance. If you like the look of a mahogany side, you might consider veneering over the plywood hull. This would give you the same look but not appreciably add to the weight. Just a thought

Yes, I considered the fact that it might be heavier if I go the cold molded route. It's not really the look I am after so much as the strength. I will most likely be painting the hull anyway. I just feel that the cold molded approach is far stronger.

Certainly, the amount of work is much greater for CM. Oh, well, I guess this is one of those questions I will need to do more research on when I have a better feel for the construction (i.e I have the plans in hand and have evaluated the bill of materials).

Thanks for your response.
Carl

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Roberta
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Re: Cold Molding Instead of Plywood Sheeting

Post by Roberta »

I would use a premium plywood like Joubert Okoume. The plywood is very expensive, but cost will be offset with less resin needed, fewer battens, and far less work. Joubert finishes well regardless if you paint or bright finish.

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Iggy
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Re: Cold Molding Instead of Plywood Sheeting

Post by Iggy »

CM for me is about the hull shape and finish. I wouldn't think a CM hull would be significantly stronger than a quality marine ply hull... at least not significantly enough that it would make any difference in case you skipped over a rock or ran into something. I would bet both materials are in the same 'ballpark' in terms of impact strength, and wear resistance will come down to the fiberglass cloth on the exterior, not the substrate wood/ply underneath.

And we are not talking about a minor increase in time invested, CM hulls are labor intensive and if you plan on painting over it anyway, I'd stick to a plywood hull on a plywood designed hull.

You can always increase the thickness of the plywood. My bottom is 3/8" thick Meranti BS1088 plywood (I had the option to use 1/4" according to plans), and it took straps and a lot of fasteners to get that sucker to bend to shape. The 7oz fiberglass cloth ontop will give it a good layer of armor to help with the inevitable rock bump.

Second to building an aluminum or metal boat, I'd stick with the spec'd material type and play with thickness first.
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Bill Edmundson
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Re: Cold Molding Instead of Plywood Sheeting

Post by Bill Edmundson »

Carl

Please, believe me these boats are plenty strong. I'm doing a plywood design that the USCG used in the '50s & '60s. They sea trialed in 15' to 25' breakers.

Bill
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Re: Cold Molding Instead of Plywood Sheeting

Post by BruceDow »

I agree. Cold Molding is about building your own plywood, but in a non-conical shape. (In sheet plywood boats, there is always one straight line in the plywood.. In CM boats, there is not) The only reason I would want to cold mold that is that "flat" plywood would not fit around the compound curves I want to make.

B.
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Re: Cold Molding Instead of Plywood Sheeting

Post by mrintense »

Whoa, wasn't expecting that many responses so soon. But Reading them over and considering what was said, I think that maybe I should go with the plywood hull and count my blessings that the work will be a bit less. :D

I guess my experience with vac bagging in the airlines made me partial to the CM approach. Too often in the past I have let partiality control my decision, usually with less than stellar results.

So, you ll have convinced me to go with hat Mr Witt originally designed into the plans.

Love the support in this forum!
Carl

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DaveLott
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Re: Cold Molding Instead of Plywood Sheeting

Post by DaveLott »

Carl - I did not realize that you were worried about the strength of the stressed plywood construction. Oh my, don't lose an minute of sleep over that . Stressed plywood construction has stood the test of time and proven to be a very reliable and strong boat building method. GO FOR IT and don't even consider looking back.
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Re: Cold Molding Instead of Plywood Sheeting

Post by DaveLott »

Bill Edmundson wrote:Carl

Please, believe me these boats are plenty strong. I'm doing a plywood design that the USCG used in the '50s & '60s. They sea trialed in 15' to 25' breakers.

Bill

Bill - I believe the PT boats of WWII were also plywood construction. I know my father spoke of the high speed extraction boats used in Vietnam were plywood. Those boats were almost too fast to track on his radar. :shock:
Dave

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Lowka53
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Re: Cold Molding Instead of Plywood Sheeting

Post by Lowka53 »

DaveLott wrote:
Bill Edmundson wrote:Carl

Please, believe me these boats are plenty strong. I'm doing a plywood design that the USCG used in the '50s & '60s. They sea trialed in 15' to 25' breakers.

Bill

Bill - I believe the PT boats of WWII were also plywood construction. I know my father spoke of the high speed extraction boats used in Vietnam were plywood. Those boats were almost too fast to track on his radar. :shock:
yes the Pt boats was made of plywood and the ones the navy has now are made that way still. but talk about over power last one i seen in the 70's have six big Chrysler motors inboard.
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Bill Edmundson
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Re: Cold Molding Instead of Plywood Sheeting

Post by Bill Edmundson »

I believe that most of the speed record boats are plywood also.

Bill
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Re: Cold Molding Instead of Plywood Sheeting

Post by jamundsen »

The superstructure of the PT boats was built with plywood offering little protection. The hulls were built much as we build ours today. Double diagonal mahogany planking with an empregnated cloth between the two layers. If they had used epoxy there might be more of them still around.
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