OMC sterndrive sucks air during acceleration?

[wakeboard4life705]

I have a 1993 OMC 5.0L Cobra. I recently discovered that a few times when i have been accelerating to pull up wakeboarders the boat seems to suck a pocket of air. It will blow out all of the water from behind it so fast that it will catch a pocket of air, rev up, and then i have to pull it back into neutral. What could be the cause of this, too shallow water, to high/low pitch prop? The mechanic said use a lower pitch prop but last year we used a 21" pitch and had no problems whereas this year we are using a 19" pitch. IDEAS?

 

[Rob454]

Re: OMC sterndrive sucks air during acceleration?

Sounds like the prop you currently have now is cavitating. Since you pull skiers you probably need a lower pitch on start off to compensate for the added drag. Especially if the skier is a bigger guy
Rob

 

[Boomyal]

Re: OMC sterndrive sucks air during acceleration?

You sure the prop hub is not slipping? It will act the same way you describe.

 

[QC]

Re: OMC sterndrive sucks air during acceleration?

After you back out of the throttle, can you slowly go back up and get to full speed? If so the hub is not spun, and it is also not cavitating, it is probably ventilating. Your description is right on with an issue I had with a prop, I could keep it from ventilating, but only by easing into the throttle. This is also not about pitch, it is about design and match with your hull. You should carry two props anyway, go buy a new primary and the other one will be your spare. I'd recommend a 4 or 5 blade with a little cupping if your goal is hole shot and watersports. If a 21 worked last year, then a 21 will work this year, but cupping may take out 100 RPM

 

[wakeboard4life705]

Re: OMC sterndrive sucks air during acceleration?

You sure the prop hub is not slipping? It will act the same way you describe.

With the engine off I had a buddy turn the prop while it was in gear and the belts moved and everything was fine, so unless im missing something i dont think that it is slipping.

 

[wakeboard4life705]

Re: OMC sterndrive sucks air during acceleration?

If I did decide to go to a four blade prop what pitch should I use?