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WakeWorld Discussion Board » >> Boats, Accessories & Tow Vehicles Archive » Archive through April 21, 2006 » Is this cavitation?? « Previous Next »
By Todd Brown (t_brown) on Sunday, March 19, 2006 - 10:15 pm:    Edit Post Delete Post
I was going about 30mph and tried to turn around and it I slowed to about 20 and the rpm's when to about 4k until I completed the turn. In my other boat, with a 4 blade pro, I never had that happen. This is a 3 blade standard alum prop.
 
By Craig Strait (yosquire) on Sunday, March 19, 2006 - 10:48 pm:    Edit Post Delete Post
yep, my old I/O would do that..

Sometimes it helps to pull back on the throttle.. then the prop sinks back into the water and you can juice it again.

 
By midwesty (midwesty) on Sunday, March 19, 2006 - 10:56 pm:    Edit Post Delete Post
NO POWERTURNING!
 
By Attila Miszti (attila916) on Sunday, March 19, 2006 - 11:15 pm:    Edit Post Delete Post
My bayliner would do that as well. If you lower the outdrive all the way you should be able to avoid cavitation. After I swapped my prop from a 3 blade 21 to a 4 blade 19 I had less problems with cavitation.
 
By Todd Brown (t_brown) on Sunday, March 19, 2006 - 11:47 pm:    Edit Post Delete Post
I'm not trying to power turn, just turn and stay on plane. I was able to do exactly what I did with my 18.5 Bayliner with a 4 blade prop and never had that happen. It just sorta freaked me out.
 
By Nick J (humboldtboarder) on Sunday, March 19, 2006 - 11:53 pm:    Edit Post Delete Post

quote:

I'm not trying to power turn, just turn and stay on plane



sounds like a power turn to me

 
By Karl De Looff (boarditup) on Monday, March 20, 2006 - 6:52 am:    Edit Post Delete Post
It is ventillation, not cavitation. You are getting air around the prop. A dinged up prop will make the situation worse. It is a hull/outdrive/prop interaction issue. Some mfgrs will raise the outdrive to get extra speed and sacrifice some of the handling. Other times, it is hull design.
 
By Tpyle (tpyle) on Monday, March 20, 2006 - 7:39 am:    Edit Post Delete Post
What is your definition of a power turn?
 
By Todd Brown (t_brown) on Monday, March 20, 2006 - 10:41 am:    Edit Post Delete Post
My definition of a power turn is punching the throttle down once you enter a turn to swing the stern of the boat around at a fast speed.
 
By tuneman (tuneman) on Monday, March 20, 2006 - 11:48 am:    Edit Post Delete Post
Todd, have you tried turning the other way? It may only do it in one direction due to the rotation of the prop.

Also, are you using ballast? A loaded down boat will have a greater chance of cavitating that an unloaded one.

 
By Todd Brown (t_brown) on Monday, March 20, 2006 - 12:07 pm:    Edit Post Delete Post
No, I do not use ballasts and I only turned right so I can try turning left and see what happens. I had 4 people in the boat at the time.
 
By Rod McInnis (rodmcinnis) on Monday, March 20, 2006 - 12:10 pm:    Edit Post Delete Post
It could be cavitation, or ventilation, or a combination of both.

Cavitation is something that is happening pretty much all the time. It only becomes a problem when it becomes so bad that the prop slips. Cavitation is the result of the "forward" side of the prop trying to "pull" the water towards it, verses the back side that pushes. You can't "pull" water, all you can do is create a hole that the water flows into. Creating the "hole" causes a major decrease in the pressure. When the pressure drops low enough the water will actually boil at lake/river temperatures. This "boiling" is the cavitation.

While the backside of the prop can generate unlimited amounts of "push", the amount of force the front side can exert is limited to the water pressure, which is a function of the depth. When you are in a turn, any tilting of the boat will cause the prop to move closer to the surface, decreasing the water pressure on the prop and increasing the cavitation.

If the prop creates a hole that the water won't fill in before the next blade rotates into that position then the blade doesn't have anything to push and it slips. "Cavitation" is the boiling of the water due to the pressure drop, which happens all the time. Only when it gets so bad the the prop slips do you notice it.

Ventilation is another issue that can happen. This is when the action of the hull forces air down into the water in the path of the prop, then the prop slips in the air bubbles.

In general, more blades on the prop reduces the amount of cavitation. The condition of the prop can also have a major effect. A dull, dinged or bent prop will cavitate a lot more than a sharp true prop.

 
By DC (dan_forrest) on Monday, March 20, 2006 - 12:41 pm:    Edit Post Delete Post
Rod...thanks for the explanation. I have been wondering how that actually happens. Nice job
 
By Todd Brown (t_brown) on Monday, March 20, 2006 - 1:58 pm:    Edit Post Delete Post
Excellent, thanks for the info!
 
By Craig Strait (yosquire) on Monday, March 20, 2006 - 2:03 pm:    Edit Post Delete Post
Yes, thanks, that was insightful!

 
By Tpyle (tpyle) on Monday, March 20, 2006 - 6:03 pm:    Edit Post Delete Post
T Brown

How do you keep from power turning when say towing a tube?

 
By Mike O'Callaghan (greenpinky) on Monday, March 20, 2006 - 6:10 pm:    Edit Post Delete Post
You don't pull tubes!
 
By B Whelan (tx_cook) on Monday, March 20, 2006 - 7:46 pm:    Edit Post Delete Post
hahahahahaha!!!! (look at mike's quote on his profile)
 
By Walt (walt) on Monday, March 20, 2006 - 7:50 pm:    Edit Post Delete Post
Great post Rod !
 
By B Whelan (tx_cook) on Monday, March 20, 2006 - 8:59 pm:    Edit Post Delete Post
on second look, mikes profile quote says "Tues", not tubes like i thought. oh well, his quote would work either way and his post is funny.
 
By Todd Brown (t_brown) on Monday, March 20, 2006 - 11:46 pm:    Edit Post Delete Post
Well, I really don't tube unless my friends kids are onboard. Even then, they would not take kindly to me hammering into the turns..
 
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