My Alaska trip in video!

[NightTrain]

Hittin the rapids!!

This is a great example of cavitation that happens with Jet Boats in very rough water.

A jet is simply a very big water pump; it sucks in water from beneath the boat and shoots it out the back at high velocity. When the boat travels over a deep trough in the water between standing waves, the jet encounters that large air pocket and the engine RPM spikes with no load on it, until the boat travels past that air underneath and once again is able to suck water into the jet. In that momentary cavitation, you have no thrust or steering which can be a big deal if you didn't anticipate it and set the boat up correctly in speed and direction, especially in rapids.

The boat manufacturers are well aware of cavitation and spend a great deal of time and money to minimize that event, but R&D only goes so far and it'll always happen to some extent when running white water. The engine and jet are beefed up to handle this kind of abuse - but still, I don't like my engine doing it.

So in this vid, you can hear me back off the throttle right before it cavitates, then I pour the coals to her as soon as it's done cavitating to regain lost speed with a course correction, then the 2nd time I back off and repeat it.

It probably spiked to about 4,800 RPM in this vid, but if I hadn't backed off the throttle prior to cavitating the engine would have screamed at 6,000 RPMs or so and then slammed back down to 3800 when the jet bit again - that's too much abuse in my book. A comparison would be to drive a stick shift pickup down the highway at 55 MPH, holding the throttle to the floor while pushing the clutch in for 2 or 3 seconds and then dumping the clutch - that's a tremendous strain on everything.