Boat Revs High

[dust_storm]

Gooday fellow boaties.

Don't know it anyone has had this problem before but when I'm going fishin out in the deep blue and I hit a wave (hard) its like I get a air pocket around my prop then the revs go up and wont stop until I pull the boat up. Anyone got any idea why its doing it?

Cheers.

By the way if there is going to be any people going into the Bowen Fishing Classic GOOD LUCK because you will need it

[Roughasguts]

Yep that be cavitation, similar to if your car was pushed up against a wall and all you can get is the wheels spinning.

Once the resistance of the wave is gone, the prop can grip the water better.

I'm sure theres better explanations, but that's it with out getting in to the technical stuff.

[dust_storm]

Thanks Roughasguts

I’m just hoping it doesn’t do any damage to the motor when it revs so high

[davez104]

If its over revving, yes it will do dammage. Big end bearings and conrod pins etc don't like high revs much. Once your prop starts to cavitate, it will tend to hold on to that 'air pocket' until you drop the revs right back down. Could be the way the motor is set up on the transom, could also be a worn or damaged prop, either way, get it checked out.

Dave.

[blaze]

When you get a bit of air when leaping off a swell, back off the revs as she lands and then increase again or slow down a bit so the prop stays in the water.
cheers
blaze

[outsiderskip]

try dropping your motor down 2 holes on transom
it will cut out cavitation

pete

[BaysideMarine]

I dont think I would go with outsiderskips recommendations......

Make sure you cav plate is more or less level with the keel and you are in the right ballpark.

If you go hard into a wave and get the boat airborne or semi airborne you would have to expect aeration of the prop at best and a free spinning airborne prop at worst.....

So as advised, back off when you become airborne or perhaps more pertinent, dont be such a speed freak and drive in accordance with the conditions....

We can all take a Formula 233 and fly off the top of 6mtr swells out wide and handle it fine but what are we proving? (other than that we are self obsessed moron, addicted to speed and with a wanton disregard for the safety and comfort of those who place their trust in us onboard our vessel....)

Extreme boat use really lies in the hands of abolone poachers and rescue/police organisations.

Cheers,

Nicholas

[BaysideMarine]

Whats your full throttle rpm on flat water?? Waht boat is it? What engien? And what pitch and diameter prop?

Cheers

[Stumpy-USA2]

Like the others above have said, its cavitation. There is one easy cure you can try. If you use a three blade prop go up to at least a four blade. A five blade is best for heavy loads and rough water. The extra blades allow the surface area of each blade to be smaller and that allows the bubbles that cause cavitation to dissipate quicker. Plus, if you do lots of turning at speed to cross waves the five blade will hold the water much better and keep the boat from wanting to slide in the turn.

Casey

[Roughasguts]

Strange really you would think a 2 banger outboard would have a rev limiter.

Seeing as once the rev's get away theres little stopping self destruction.