Marco Flamingo":1e5z1mit said:
These showed up right after I put on my new prop, and never got any worse, so I just let it be. But I'm wondering if it might be the symptom of something I should correct. It's mostly just the paint that's missing, but the underlying aluminum is rough, so it must have taken (or is taking) some of the metal off.
Mark
Mark--the change you made is the new prop... What is the difference from the old prop? Several things involved--turbulence from a transducer ahead of the prop, different configuration (cupping or rake) in the prop, prop too high, running at constant RPM where the cavitation is worse.
Here is a quote from Tom Clarke (Whose opinion I greatly respect) on THT
"Let me straighten a few things out about cavitation and ventilation, which are two distinct phenomena.
Cavitation is NOT the formation of air bubbles. The bubbles formed are vacuums, or more precisely water vapor, not air. Cavitation bubbles are formed when the pressure is so low the water goes from the liquid phase to the vapor phase. Remember how water boils at lower temperatures at higher elevations? ....
The damage to a propeller blade occurs when these bubbles collapse actually eroding the stainless steel (or other metal) of the blade.
Ventilation is the sucking in of air from the surface or exhaust gases from the exhaust into the propeller and the dilution of the solidity of the water around the propeller with these gases."
So will it eventually damage the blade? Yes. Is it doing any harm to the boat or engine? Most likely not.
What can be done? Change props. Take the prop to a really good Prop Scan Shop, and see if they can change the cup....but this will most likely cost more than another prop--down the line.
You might try running at different RPM's than you are most of the time now--higher or lower.
If the engine is performing correctly--I would not change the height. But in some cases that may help.
If there is anything close to the prop causing turbulence, that can be moved further outboard--consider that.
What is the WOT RPM and GPS speed?
Personally if the boat is reaching its rated RPM at WOT, then I might see if changing the trim of the motor makes significant difference--but probably run with it, and buy a new prop down the line...The next prop may be fine...
