The little jet boat racing is quite popular for Aussies and Kiwis, probably more Kiwis though.
I was fortunate enough to have a ride in one a few ago. Basically 12' 6" long, running a high HP V8 petrol through a stage 3 jet (mostly Hamilton over here).
The G force is amazing, they seem to achieve the max. speed in the first few seconds, like a scrambler motorbike. This makes the short shallow courses perfect. The one I was in probably only did about 50 knots, but it happened so quickly.
Their biggest problem is that operators roll them on the tight corners, straight onto the shore!
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