Thanks for all the help. As an update on the plans, we have now decided it might be better to build 2 smaller hovercraft, instead of one big one. The reason for this is that if one breaks down - out of reach somewhere on the river, we want another craft to be able to rescue it! So instead of using car engines, we will probably now use a 35hp engine from Briggs & Stratton. See here for details... http://www.commercialpower.com/displ...sp?DocID=76948
An industrial engine will probably be more reliable than an old car engine too - although a lot more expensive...
Anyway, thanks again, I'll post some pics later in the year when we start to build.
Rick