Cavatation Plate question

[Bozo]

If the cavatation plate is not visible when running WOT, should the motor be moved up? <br /><br />The boat doesn't porpoise when the motor is trimmed all the way down but starts bob if you try to get the bow of the boat up just slightly.<br /><br />Shouldn't the cavatation plate be right at the waterline when running?<br /><br />Thanks for any advice.

 

[ob]

Re: Cavatation Plate question

that would depend on your hp to weight ratio .In general cavitation plate should be flush to slightly above mean bottom of boat .You can look at this with boat out of water and motor trimmed level with hull.If prop is biting too deep it will when trimmed up attempt to lift front of boat until boat rises and changes push plane of prop allowing bow to fall .This process repeats itself hence the porpoising effect.

 

[rickdb1boat]

Re: Cavatation Plate question

Good reply, OB! I was going to reply to this, but I'm not so sure that all plates are above the Water line when running on plane. Maybe someone can verify!

 

[Bozo]

Re: Cavatation Plate question

The boat has a Yamaha 115 but, I don't know the exact weight. It is an 18 foot bay boat that I will guess weighs 2000-2300 lbs.

 

[ob]

Re: Cavatation Plate question

Maybe this can help with visual although each boat has its own characteristics.I run a 70 hp evinrude on a 15 dauntless and when running 5500 trimmed out cavitation plate is skimming water.I also have a two piece Doelfin attached.Test after making any adjustments in 3/4 throttle tight turns to insure prop does not cavitate.Thats what my OMC manual dictates .Move motor up one hole at a time until you can achieve this .If it cavitates only slightly in turn some people leave it right there.

 

[Bozo]

Re: Cavatation Plate question

Thanks...that is what I was suspecting.<br /><br />I have a "sting ray" stabilizer mounted on the motor as well. It is a single piece style that mounts on top of the cavatation plate and that is not visible either when up on plane. I was thinking that this device was to be "skimming on top of the water for the proper results. I will try moving it up a hole.

 

[digimortal777]

Re: Cavatation Plate question

um iduno if im wrong on this but if your cavitation plate is above the water than your engine isnt getting any water to cool it as most engines have the inlet above the plate<br /><br />just a thought

 

[ob]

Re: Cavatation Plate question

yep ,you're wrong .intake is below cavitation plate.just above propeller shaft barrel.

 

[rickdb1boat]

Re: Cavatation Plate question

News to me! I've never seen an intake above the plate! Any Takers?

 

[ob]

Re: Cavatation Plate question

Don't feel bad Digimortal.If it helps my last name is O'Brien.There always after me lucky charms.Not

 

[rickdb1boat]

Re: Cavatation Plate question

Ahh, the luck of the Irish!

 

[Dhadley]

Re: Cavatation Plate question

The X dimension (height) has a lot to do with hull design and prop style. A SST type prop will run higher than an aluminum. A Stiletto will run higher. A Turbo will run slightly higher than that. A 4 blade will run higher than a 3 blade. <br /><br />These are "general rules of thumb". The perfect prop for any given boat is a marrige of hull design / prop technology / defined useage.<br /><br />Good luck!