I don't think you could find a description of this sort (mentioning hovercraft) in the USA.



Foam Dock Pads UK

http://www.saralbs.co.uk/dockpads.html



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Standard pads have a rear frame of seasoned timber or galvanised steel bonded with a polyether foam then covered with a 900gm/m2 woven polyester based pvc. This is then covered with a heavy-duty 1500gm/m2 nylon based neoprene black hovercraft-skirt material.
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Has anyone done a double layer skirt before?



The inside one would cover the foam connected to the hull for buoyancy and be lets say 1M dia., the second layer would be 2M (or twice as large) and have pressurized air flow between the two layers.



I'm not going to patent it, just asking if it's been done before.



I'm still pondering the advantages - if any.



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EDIT:



The trend seems to be that air bladders are replacing foam though (in some applications).



http://www.floattech.com/commercial.html