Power Dinghy Racing hulls?

[Rapid Racer]

Hi people,

Another newbie here, so thanks in advance for any info or help. :)

Anyway, we are collecting information to build a boat for the Avon Descent (Perth, Western Australia). In saying that, i've found next to nothing in all the searches i've done, so i'll throw it out to you guys hoping someone can point me in any direction. (hopefully the right one).

Basicly the race is a 135km whitewater/flatwater/tree infested river race over 2 days. see www.avondescent.com.au.
the boats get a hammering so need to be strong, but light as possible the help with power/weight ratio (only upto 10hp outboards)

boats getting hammered:

http://www.aussiesinaction.com.au/popup.php?id=343281

http://www.aussiesinaction.com.au/popup.php?id=343288

http://www.aussiesinaction.com.au/popup.php?id=293645

http://www.aussiesinaction.com.au/popup.php?id=291406

some video on youtube aswell.

Thanks,

Daniel

[Rapid Racer]

Ok, some more information:

These boats seem to be made like a surf board (a little bigger). A foam core with glass/epoxy coats. Obviously the bottom needs to be very strong to withstand bouncing over rocks. They ideally weigh 40-45kg (88-99lbs) without the outboard.
The minimum length is 2.540m, no limit on beam, but they seem to average approx 3m.

With 2 people the top speed in standard class is approx 60-65 km/h (37-40mph) and sports class at approx 70-75 km/h (43-46mph).

Both classes run factory standard 10hp outboards, no mods allowed to the power head but the leg can be. All the legs get reinforced with plates welded on to stop the leg snapping on rocks and such. The standard class can only use standard props for that engine, but they can be modified (pitch, cupping etc). The sports class can go for any prop they can find. The transoms are a jacking type (hydraulic or rope) so the prop can go from submerged to surfacing quickly.

The gear boxes get ground down on the outside then a molded covers it with urethane? with some of excess, this gets shaped by hand after curing.

Most of the boats have a flat bottom with the front 1/3 rounded sides and the back 2/3 a sharpish edge at 90 deg. or more.

We now have some info on construction and some experienced people to help, but I would still like to hear any suggestions, however radical, from experienced boat builders

Regards

Daniel