Cavitation While Pulling a Tube?

[Taylor_T]

I have a 1985 chris craft with a 200hp mercruiser set up, Alpha One outdrive. Yesterday I was at the lake pulling a tube, so I was running at pretty high RPMs frequently. Occasionally the RPMs would shoot up, almost sounded like the prop came out of the water a bit or it came out of gear. This doesn't happen when pulling a skier or wakeboard, or when just cruising around. The boat gets onto plane without a problem. After some reading it sounds like this is caused by cavitation. Does that sound correct to you guys?

If it is cavitation is, is there anything I should be concerned about with this? How do I avoid it or remedy it?

(Also, as a side question.. I'm 98% sure my outdrive is an Alpha One.. but it doesn't say "Alpha One" on it? From what I understand the alpha one drive was put into production in 1984. Is there a way to tell, or can someone clue me in on what I probably have?)

 

[Scott Danforth]

trim down

you are ventilating, not cavitating

a tube puts more pull on the back of a boat than a skier or wake board. in fact, a skier or a wake-board can only put so much pull on a boat before you pull the rope from their hands.

a tube, if it submarines, will pull the tow eye from the transom along with a piece of transom with it.

 

[TunaFish389]

Are you trimmed up? If so try trimming down till issue stops. Got beat..

 

[Clinton37]

This happens occasionally while we are pulling a tube with my fathers boat. He has an Ebbtide 19ft with a 5.0 Mercruiser (not sure if its an Alpha One or not). It seems to only happen when there are people in the front of the boat and usually while turning sharply (you know..trying to sling the tuber off So we just get those in the front of the boat to move to the back which helps lower the prop into the water that extra inch or so. If you dont have extra people to move around, put as much extra weight in the rear of the boat. Coolers, skis, etc. Of course, the trim may need to be adjusted downward when turning. If neither of these ideas help, some might suggest a decent hydrofoil that you can pick up anywhere. Some actually help with ventilation. The next option would be trying a different prop. Hope this helps!

 

[Levinz11]

My trim is full down the entire time I'm pulling a tube. Never had my prop ventilate. I use a 4 blade Solas.

 

[bman440440]

Or it could be a coupler or the prop hub... I would suspect this if your drive is trimmed down... if you are trimmed up then I would suspect ventilating of the prop

 

[JASinIL2006]

I agree that it sounds like you're trimmed up as if you normally would for running on plane. For tubing, especially if you're cutting back and forth, you really need to be trimmed down to keep the prop buried in the water.

Trying to cut back and forth too sharply can also cause the prop to ventilate. Sometimes entering a turn a bit wider can help avoid that.