Research on "cavitation"/"growling" when heavily ballasted...

[IDBoating]

Lately, there have been a couple of sub-thread discussions regarding weird noises and behaviors on some of the ultra-ballasted boats. I ran some experiments yesterday and thought I'd share my results.

After correcting how my steering cable occasionally rubbed against the stuffing box fitting, my louder "clicking" noise went away. Mostly. However, I still have two noises that occur only when my 24Ve is heavily ballasted and leaning to one side.

One is a growling sound that occurs when I'm turning around to pick up a downed surfer; this one sounds like it's coming from the prop itself, and thus may be cavitation or related thereto. The other sound is a very light "ticking" sound that is propspeed related. It only occurs when the propshaft is turning, is directly proportional to propshaft RPM's, and also only occurs when I'm turning around and driving back to pick up a downed surfer.

I was hearing these noises while we were out yesterday, so when I started driving I tried something new. Normally when a surfer goes down, we back off the throttle just to the point where the transmission is still engaged (no powerturns!) and motor back to the person. As an experiment, when I backed off the throttle I took the transmission completely out of gear, waited a moment, then ramped it back up to the same speed I would normally use. This gave the transmission and v-drive a moment of non-operation.

Result: I never heard the sounds again the rest of the day.

I can dream up an explanation for the growling. If the start of the turn caused the prop to cavitate, it could be self-perpetuating. Stopping the prop for a moment could give the water a chance to settle out.

I'm going to test this again today, but in the meantime thought I'd throw this out there. Anyone else try or experience this? Any explanations for why pausing for a moment would make a difference?

Hopefully we can compare results and come up with a solution and an explanation. Thanks!

[NICKYPOO]

Harmonics. You get a bunch of spinning metal parts and you start varying the rpm, load and force, at some point the frequency catchs up with resonance, creating a certain tone. Or something like that.

Interesting observation on the conditions. I always pull the boat out of gear after coming off plane for a downed rider. 'Course, I'm running a D-Drive so, my observations might be pointless in this first place.

[IDBoating]

Harmonics. You get a bunch of spinning metal parts and you start varying the rpm, load and force, at some point the frequency catchs up with resonance, creating a certain tone.

Good thought. Giving the propshaft a chance to stop spinning might vary things just enough to "break the spell", as it were.

By the way, I heard these same noises on a 2009 RZ2 yesterday that I had the opportunity to drive, and it was not ultra-ballasted. So it's not unique to my boat. Not sure if I'm happy or sad that's true.

Interesting observation on the conditions. I always pull the boat out of gear after coming off plane for a downed rider.

I always ramped down the throttle, of course, but wasn't completely disengaging the transmission. We both do now. I have no idea if it helps anything, but weird noises are seldom "good" so I figure at worst it's not making things worse.

Thanks!

[Duncan]

By the way, I heard these same noises on a 2009 RZ2 yesterday that I had the opportunity to drive, and it was not ultra-ballasted. So it's not unique to my boat. Not sure if I'm happy or sad that's true.

As reported in your other thread, our 2009 RZ2 has occasionally "ticked" when under surf ballast and low speed. But dropping completely out of gear did not solve -- it would still tick. I took it in and out of gear slowly several times and eventually it stopped. Has not re-occurred last few times out.

Re cavitation, we never get it while turning back for a down rider but I go to neutral to come off plane, bump into idle waiting for the wave to pass, then go back. We do, however, get cavitation occassionally if turning (into the wave) with a rider at speed. Surprised it does not happen more often -- 1235 is doing its job!

[IDBoating]

As reported in your other thread, our 2009 RZ2 has occasionally "ticked" when under surf ballast and low speed. But dropping completely out of gear did not solve -- it would still tick. I took it in and out of gear slowly several times and eventually it stopped. Has not re-occurred last few times out.

I'd love to know what is causing that ticking sound. Apparently it's not just our boat, which gives me some comfort I guess.

[duffymahoney]

I get a ticking sound when I am just in gear idling around.

[ragboy]

When the boat cavitates you will sometimes hear a growl and some vibration from the back of the boat, and sometimes it feels like your prop hit a piece of wood. I know, because on lake oroville in the spring, you hit a lot of small waterlogged pieces of wood. It happens on the RZ2 and the 24Ve when loaded and listed. It rarely happens in butter, and more often in small chop and wind. It didn't happen enough on the RZ2 to warrant going to the 1235 for me. I am already on the 1235 on the Ve and may seek a bit more prop since it is more pronounced on the load we are carrying.