Strip-plank + foam core + kevlar?

[Seafarer24]

I am considering the following building method:

First, erect the typical bulkhead mold and strip-plank it. Perhaps vacuum-bag 4oz cloth over it (any reason for or against this?)

Then, apply .5" foam core and bag Kevlar over that. I could stand to use something other than Kevlar, like a very excellent S-Glass if the properties are similar enough. I want it to be very strong and fairly light.

This will be for a 32' 10,000lb displacement cruising monohull. I don't want to worry much about hull punctures. I figure any weight I save on the hull could be added to the ballast.

I thought that strip-planking would be the easiest, fastest way to obtain the hull shape with a light-weight material. Also, it will give a great-looking interior surface.
The foam is for extra stiffness and to provide a fairer exterior surface. I wouldn't even have to fair the wood before laying foam over it.
The Kevlar is obviously for strength and puncture-resistance.

I suppose my biggest question is in regards to the use of Kevlar. I know it would be easier/cheaper to go with S-Glass, but how much heavier should I expect it to be to get the same puncture-resistance? How much exterior skin should I lay on, anyhow?

[PAR]

Strip planking isn't the lightest way to get a hull. Putting the Kevlar on the inside will provide more penetration resistance then on the outside and the foam isn't doing particularly much in this schedule, so you could just skip it.

Molding a couple of layers of veneer over your molds, followed by some foam, then a few more layers of veneers, with a fabric skin inside and out, will produce a much lighter and stronger structure, then your suggested laminate schedule.

[Seafarer24]

How would Kevlar provide more protection inside the hull? It is not particuarly stiff, (wood is ~7x stiffer than kevlar), so it wouldn't even come into effect until after the wood had broken. It also wouldn't have another (stiffer) surface to disperse load into. I probably couldn't shoot a gun through the hull from the inside, but something from the outside would do a lot of damage to those outer layers the Kevlar is supposed to protect.

I've heard that cold-molding with wood veneers is just about the lightest way to build a hull. Is it even lighter than foam and fiberglass (or foam and kevlar)? Is it stiffer and stronger as well?

I have read that a first layer that is strip-planked, with succeeding layers of veneers layed diagonally would be a faster, easier method and not much heavier than normal cold molding. I'm trying to avoid covering the mold with ribbands, seems like a lot of waste and damned near the same thing as just strip-planking it.

[dougfrolich]

Kevlar is really good in tension. If something is trying to penetrate the hull from the out side, the inside skin is in tension, thus kevlar on the inside.

[PAR]

The basic principle with sandwich or cored engineering is the skin properties. When exposed to a bending load (result of an object trying to penetrate from the outside) the inner skin is put in tension because it must try and conform to the increasing radius caused by the bending load. The inner skin's tension properties come into play, so you'll want a material that doesn't like to be stretched, as Doug has mentioned.

[Man Overboard]

Seafarer
A tip given to me by Doug Frolich “Look at ProBoat #69 2001 "Designing and Building in Wood/Composite Construction" by John Fox” This article deals with the question you are considering. The author has made up different test panels, tested the panels under various conditions and has included test dada in the article. You can read the thread at http://boatdesign.net/forums/showthread.php?t=14565 The Pro Boat article will begin to answer some of the questions you are pondering.