Keefer Douglas
Member
I have posted at length elsewhere about my repower with a Beta 43, but starting a new thread to solicit some advice.
Quick recap: Beta originally suggested an 18"/12" fixed three blade prop. Which we installed, with resulting very small clearance to the bottom of the skeg aperture. It was very noisy during the sea trial. So we had the prop cut down to 17"/12.5". Didn't make any noticeable difference in the noise (or performance under power).
My own research and consultation on here led to the conclusion that the noise is cavitation, which should be solved or at least mitigated by reducing prop size again. But the Beta mechanic (and he also claims his contact at Beta itself) are convinced that the noise is actually being caused by water in the torpedo tube. His theory is that the Beta is getting more horsepower to the prop and causing the stern to sit down lower than it did with the Perkins, submerging the tubes. To test this he asked me to plug up the tube and sea trial again. I tried stuffing towels in each side, and heard no difference in the noise. He thinks that wasn't good enough, and I need to get a true airtight seal on it.
The scupper drains are directly under my feet at the helm and drain directly into the tube. I can hear water sloshing around in the tube at times through those even at cruising speed. The "cavitation" noise to me sounds distinct from that, and is tied directly to engine RPM. Faster spin on the prop leads directly to more noise, even before the boat picks up speed. His explanation seems improbable to me, but I am no hydraulic or mechanical engineer so I don't want to get ahead of myself.
Is there some factor I'm missing here?
Quick recap: Beta originally suggested an 18"/12" fixed three blade prop. Which we installed, with resulting very small clearance to the bottom of the skeg aperture. It was very noisy during the sea trial. So we had the prop cut down to 17"/12.5". Didn't make any noticeable difference in the noise (or performance under power).
My own research and consultation on here led to the conclusion that the noise is cavitation, which should be solved or at least mitigated by reducing prop size again. But the Beta mechanic (and he also claims his contact at Beta itself) are convinced that the noise is actually being caused by water in the torpedo tube. His theory is that the Beta is getting more horsepower to the prop and causing the stern to sit down lower than it did with the Perkins, submerging the tubes. To test this he asked me to plug up the tube and sea trial again. I tried stuffing towels in each side, and heard no difference in the noise. He thinks that wasn't good enough, and I need to get a true airtight seal on it.
The scupper drains are directly under my feet at the helm and drain directly into the tube. I can hear water sloshing around in the tube at times through those even at cruising speed. The "cavitation" noise to me sounds distinct from that, and is tied directly to engine RPM. Faster spin on the prop leads directly to more noise, even before the boat picks up speed. His explanation seems improbable to me, but I am no hydraulic or mechanical engineer so I don't want to get ahead of myself.
Is there some factor I'm missing here?