OUTBOARD CAVITATION

[rtgnyg]

Hey all,
When I take my kids tubing I make a lot of sharp turns to set up the wake to give them some things to jump over. While doing this the water is obviously choppy and I'm turning hard. The engine revs and the boat doesnt move. I throttle down and straighten up and its fine. From what I gather its normal and called cavitation? I guess its no big deal but my question is can it hurt the motor at all? Like starving water for cooling? Its a 2 year old 115 yamaha outboard.

thanks for any input

 

[ondarvr]

It's actually ventilation, cavitation is something very different, but the two are frequently confused. There are a couple of things you can do to help reduce it, trim the motor slightly different, use a different prop, or lower the motor one hole, a combination of these may work too. It's not really good for the motor to rev free and then hook up again

 

[scoutabout]

Yep - what he said.

I have the same need to create tube waves for my kid and his buddies.

What I often do is circle a bunch of times at a diameter of several hundred feet. Not tight enough to ventilate the motor though.

After a bit you will get a hellish confused pile of good wake in the middle, especially if you keep the nose up and speed just off a full plane.

Once it's good and rough in the middle. I head straight out, turn back, hammer down, and rifle straight through.

They don't know which way is up after that! Heh, heh.

 

[SkiDad]

you need to make sure your trim is about 1/4 max up with tubes - if you want to make even bigger wakes try running it at 1/8 trim. My boat will vent too if i have the engine up too high, the other thing you can try is a prop with more cupping. if you don't get any good results maybe lower the engine a hole.

 

[Sea Rider]

Rtgnyg,

Trim OB at 90?, assume it's a manual trim OB ?
Distribute deck weight evenly.
Go for a wot spin on flat calm, no wind water cond.
Perform tight close turns.
Lower OB one hole at a time, test till aeration disappears completely

Once there OB will behave much better on slight choppy and windy water cond.
Adjustment test must be done without pulling toys behind combo.
Once there can even maximize a prop to pull wot revs towards max wot range as usually loaded.

Happy Boating

 

[frozenokie]

I've found that by using a 4-blade versus a 3-blade propeller, the propeller stays "hooked up" much better than any 3-blade I've used. In addition, if you're using your boat for pulling skiers and tubers, the 4-blade will outperform the 3-blade when it comes to hole shot and less effort for the motor to do it's job.

But I know for a fact that at higher speeds, when I had my 98 Stratos 195SF with 175 FICHT, I went from a 3-blade to a 4-blade for the very reason mentioned by "rtgnyg"...I could turn corners at a much higher clip without ventilating the propeller. BIG DIFFERENCE!!

 

[444]

When I upgraded from an aluminum prop to a stainless prop, I noticed I could turn shaper before ventilating. IMO the reality is in most applications you need to be aware of it and just try to avoid it.