Many boats like the Escape Playcat and Hobie wave are made using rotomoulded polyethylene (PE). PE is very tough but not very stiff. As a thin walled structure a PE hull will most likely fail by local buckling and buckling is a function of a materials stiffness not its strength and only occurs when a material is in compression.
There are four ways to prevent this and each is used by both nature and boat builders,
The first is simply to make the thin wall thicker.
The second is the most common method and it is to use ribs and stringers.
The third is to use a sandwich construction where a low density layer is sandwiched between two or more stiffer layers.
The final method is used by leaves and is known as hydrostatic stiffening, I propose to use a variation on this method (pneumatic stiffening) to get lighter hulls.
To show how effective this method can be buy yourself two bottles of pop (lemonade or other fizzy drink). Empty one and stand on it. It probably won’t break but is not very stiff and will crease. Now take the other bottle skake it vigourosly and stand on it. This bottle has been pneumatically stiffened.
What is happening is that the bottle or skin has been put into permenant tension by the compressed air in the bottle. The skin is carrying all the tension loads and the air inside all the compression loads. Since the skin can no longer go into compression it won’t fail by buckling. And this creates a very efficient structure.
I therefore propose that we make the hulls thinner walled say 3mm thus lowering the weight but restoring its stiffness by providing a valve by which it can be pressurised with a common pump. This will somewhat limit the types of shapes that we can use for a hull, but a long thin hull with no convex curvature like that used by a multihull design would be an ideal shape for making the most of this process.
We are effectively reducing weight without losing stiffness by using air which is free.
Does anyone think this idea has any merit, it is currently subject to a patent GB0223164.5.
