Prop Problem with 34' Mainship Pilot Twin Yanmars

[Dan S]

Hello All. I am new to the forum and have a problem. Three years ago I had to replace the props on my twin engine 34' Mainship Pilot. I replaced them with Michigan Wheel Hy Torq MY-T4 18" diameter 25" pitch props. With these props I could only achieve about 3,000 rpm vs. the engine spec of 3,300 rpm. I had the pitch reduced to 22.5" and the rpm increased to 3,300. I just had the boat pulled for new bottom paint and it appears that the props burned holes in the bottom at the outside edge of the prop tunnels. There is very little space between the props and the tunnels, but the new props are the same diameter as the old ones. Has anyone seen this type of problem? Is my assumption that the prop is the root of the problem correct? Does anyone know the size, pitch and manufacturer of the OEM props? Any ideas on how to keep this from happening again would be really appreciated.

 

[Pascall]

It could possibly be cavitation of the ship's propellers.
What surprises me is that the ship's propellers are okay and show no damage from cavitation.

Greeting,

Pascal.

 

[DavidM]

Yes, probably cavitation. Do you feel any vibration at higher rpm’s?

If the props run smooth, I would leave them as is and fill the holes with high strength epoxy. Patching the holes every few years will be cheaper than new props. The epoxy might hold up better than the original polyester.

Whoever sold you those props should bear some blame. The original pitch of 18 x 25 is way over square and the pitch reduction to 22.5 was probably not done right.

David