I found this on the net, by posting dual prop cavitation burn, hope it helps.
It was on The Hull Truth.
I've got a 5.7GS VP Duoprop on my 22' SeaSport. I just had the props rebuilt. My top speed is about 48 mph at 4800 RPM.
I noticed some cavitation looking burns on the rear prop near the hub on the blades. I've heard this is normal to some degree. I've also heard of several fixes. Someone said if you mount your rear prop with a certain alignment to the front it will help. Others say go stainless and it will help.
I don't know, I researched this prop "aligning" before and I came up with the conclusion that it's all myth. Nowhere does Volvo recommend it, at least that I have found and after talking with numerous people that are knowledgeable say to just put them on any old way. I've experimented with different variations and found no difference at all. I know after having my props done last time, it takes no time at all for that black paint to wear off. EXCESSIVE cavitation and burn, I doubt it. I wouldn't worry about it. You could go stainless, keep in mind it's around $1100 for the set unless you can find a deal used that happen to be your size.
A friend of mine has a 28 Carolina Classic with VP and has had that problem since it was new. He has had to replace the props every year and has no help from Volvo or Carolina Classic. The only relief he has found is to trim the out drives up while running until he hears it start to cavitate then back down for app 1 second.This running angle reduces the Volvo disease to somewhat of a minimum.
As far as stainless props someone steered him away but I can't remember why, maybe SIM will jump in with some info. I have heard that indexing the props will help but I can not say for certain,sadly this seems to be a common problem, at least on his rig
If it's just burning the paint off I wouldn't worry about it. If you're seeing significant damage to the base of the blades, then the only real way to solve the problem is to switch to SS. Indexing has little, if any, affect.
I can't think of any good reason why gmanoffshores friend would be steered away from going to stainless, especially with the problems he is having with the aluminum props. Is Carolina Classic discouraging it? It sure fixed my cavitation burn issues.
The aluminum propsets I had showed burn almost immediately, I have 700 hours or so on the SS propsets with no burn visible at all. Never heard of anyone burning the SS propsets.
