Prop burning - Cavitation - Prop Singing on Duo Props

I can't seem to get this to go away from the aft prop.

When I bought the boat from the original owner, the props had quite a bit of this going on. He had 2 sets of props and both had it. I took one set in to be fixed up, and kept the others as is as emergency spares.

First trip out with the redone props, I got a loud ringing out of the props (Prop signing some people call it) most of the way through the RPM band and once again the fresh set burned. So my next step was to do what some people call "prop timing". Based on what I had read in other places, I put one of the fins on the forward prop straight up, and a fin on the aft prop straight down. I also added one of those hydrofoils because they are said to reduce cavitation, and I had one on my old boat and liked it a lot as it got me on plane a lot quicker.

Took the boat out today and only got "singing" during a very small band of the lower rpm range. But the props look bad again. I had repainted over the old burns, so I could identify what was from just today. You can see the results below in the pictures. This is running for a whopping 20 minute test run. I'm including a ton of pics, so if anyone has any suggestions, or can see something that might be be leading to this please let me know.

I'm open to ALL suggestions at this point. One thing you might notice is that the little trim tab under the plate is a bit bent from where the previous owner hit a rock. It does not affect steering, so I have left it as is.

Those appear to be fairly aggressive props.

Do you know which set they are?
Are they a matched set?
What is your WOT RPM?

Rick,

They are a matched set of B6 props. At WOT I believe the RPM is in the 4200-4400 rpm range. Speed at WOT 40-45 mph depending upon load. Boat length is 24 with 5.8 PHUCCEFSI and DP-C1 1.95 drive. Again, it's in the lower end of the band I'm hearing the singing, but that probably does not necessarily mean that's where the damage is taking place.

Doing a little more research, and I'm kind of splitting hairs on prop sizes. 2 options on these charts and neither are exactly me. On the chart there is 5.8 with 1.95 ratio and 5.8FSI with 1.78 ratio. I'm a mix 5.8FSI with 1.95 ratio. I went with the approx MPH the boat is known to go at top end. Looks like they should probably be C6 if stainless but maybe stepped down to B5 if Aluminum? I would assume the 1.95 is more important than the FSI. Please let me know your thoughts! Thanks!!

One other thing I've been reading about is improper trim causing this. My gauge does not work, so I have no idea where it's set, other than to say it's down as far as it will go. I will make sure in the morning the proper sender tooth on the wheel is in the top spline of the rack that is on the helmet.

Question - Can I run with the aft prop removed? So just running on the forward prop? I don't want to do this permanently, just as a bit of a test. Want to see if the noise I think is "prop singing" goes away. Thoughts?

Can I run with the aft prop removed?

Not sure what you'd accomplish, prop loading and hydrodynamics would have to be seriously different ...

Having a brand new stainless set delivered Thursday. Stayed at 6 instead of dropping to 5's. We'll see what happens.

Chris Rohde said:

Having a brand new stainless set delivered Thursday. Stayed at 6 instead of dropping to 5's. We'll see what happens.

Click to expand...

I know this is an old post.
How did the stainless props work? Was going with 6's a good choice?
Thanks

CASTLE_CAPE said:

I know this is an old post.
How did the stainless props work? Was going with 6's a good choice?
Thanks

Click to expand...

Worked flawlessly. Put them on last year took them up to Lake Powell for 4 days and a few days out at the lake here locally. No singing, no burning, nothing. Actually slight improvement with speed and RPM also. Love them.