Prop Cavitation

[Bill Krause]

I have a 98 Honda four stroke 8hp outboard on my H240. It has the long shaft. I find that if I have to make sharp turns on if I have to goose the motor for quick stopping of starting that it causes the propeller to cavitate. I'm not sure of the pitch on the prop, but having bought the boat and the motor from a Hunter dealer I expect that it is the proper pitch. I will be checking it out this weekend after talking to a Honda outboard dealer locally. Has anybody else had that problem and if so what is the proper propeller pitch?

 

[Joe Boyette]

My 9.9 on a 25.5 "cavitates" also on a sharp turn

and on reverse with higher throttle settings. I don't think it is true cavitation which is vacuum bubbles forming under high speed/load conditions. I think the prop is sucking air or "ventilating" due to the sharp turn angle and the motor not being in line with the water streaming past it. In reverse, a lower throttle setting helps prevent it and gives better stopping. Can you lower your engine any deeper into the water? Mine is as deep as it can get but it still happens sometimes. I'm not an expert on props but I doubt that a prop change would change the effect very much. There is a device available which connects the rudder to the outboard which would probably reduce or eliminate the effect in turns. I'm not too concerned about it because it isn't a constant effect.

 

[Ray Bowles]

Bill, Hunter sailboats from 20 to 26 feet long

simply glide through the water and will absolutly refuse to stop fast when using your OB. Regardless of prop pitch, when in reverse the prop will cavitate.Your prop should be pitched to provide the max amps out of the onboard alternator when motoring. Trying to stop a boat that is going into a slip to fast requires a wall, not a prop.When the boat has enough speed to turn with the rudder you should leave the motor in the dead ahead position. Why turn the motor?Before returning your motor to the outboard motor people try simply using the motor just enough to make the rudder stear without moving the motor. Slow down, plan ahead and see what happens. Sailing requires time, just enough to get there and just enough to get back. If there is not enough time...you pushed to hard earlier. Wow, I'm really a butt, but that is a short timer's attitude with to much time on his hands.RayS/V Speedy

 

[Bill K]

thanks

Ray, I should have explained more. I need to have my rudder up to get out and into my marina and even in my slip. I do come into it at dead slow speed as you said. I just wandered if anybody else ever encountered the cavitation or what ever it is and if there was a solution. I also don't need to charge my battery so I am not worried about that. I ordered the best pitch prop I can get. It may be the size I already have, but I figured if nothing else If it doesn.t work of if it does now i have a spare.

 

[Mark Kissel]

Cavitate

Hi Bill,I suspect the cavitation is caused by the exhaust ported through the prop hub. In a sharp turn, the exhaust is passing more over one side of the blades. In reverse, the prop is trying to pull itself into the exhaust.I find just backing off on the throttle for a moment stops the cavitation. Then try a little less throttle.Mark Kissels/v Kittiwake 98H240