cavatation/ motor height

[onceagain_04]

First off i appricate all the help from iboats
the issue, from what i have been told here is cavatation, seanymph 146fm, 30 horse johnson, prop is 10x13, and yes there is that dreaded hydrofoil on it.....i happen to like it, even though i gained 2mph with out it.
anyways, the bottom of the hull, to the cavatation plate/ antiventilation plate ( depends on who posts on here) the same plate that the hydrofoil mounts to, is 1 inch below the hull, the pin is second out from the transom, played with diffrent settings, and only worse in other spots......i have read several posts here about this issue, and am slightly confused....is the motor is the correct position? or should it be raised? a slow start is fine, about half throttle fine, but to do a holeshot or after half throttle to wot, winds up, takes a long time but will eventually get up and plane, back off and feel it catch again?...was no better with the hydrofoil off, just a little speed and a lotta bow hop
any ideas or suggestions are very much welcome

 

[Double J 300]

Re: cavatation/ motor height

The cavitation plate should be even with the bottom of the hull, not lower. That said, I've seen exceptions to the rule. For example...for fun, I raised an outboard 1 1/2 inches above the norm by using a piece of teak under the bracket mount and the 8' inflatable gained a better hole shot and about 4mph at WOT....beat all my buddies on their dingy with equal HP.

I installed a new Ficht 115 on a 17 foot alum center console and it would not perform at all when even with the bottom...dropped it down and it actually performed OK but we could never get it to "run" correctly at all speeds. Owner bought a new hull for the motor...he got frustrated.

Trial and error. A 30 HP can be lifted by hand so take it out and try it....it's fun. Alan

 

[jack7771]

Re: cavatation/ motor height

When I bought my 16' bowrider with 110 hp, I determined the motor was fixed too high on the transom. I do water-skiing and tubing, and there was too much cavitation. I had the motor dropped down the transom to the next bolt position, so that the cavitation plate is now even with the center of the drain hole when the motor is set at # 2 tilt position. I lost 2 mph, but there is much less cavitation, and it's worth it to me. The boat hull is a shallow/moderate v-hull design.

Jack

 

[scrobo]

Re: cavatation/ motor height

So what is a "hole shot"?

I have my motor mounted like so.

I assumed that it was a general rule that you had to have it even.

 

[JB]

Re: cavatation/ motor height

The anti-ventilation plate should never be lower than the bottom of the boat. It is intended to run right on top of the water coming off the bottom when on plane. On some boats it can be fine tuned to 1 or 2 inches above the bottom, but where it should be for optimum performance is like fitting a shoe. . .individual to each boat/engine/load.

A Hydrofoil must run on top of the water on plane to be of any benefit at all. If it is under water on plane it will severely interfere with handling and introduce a lot of drag.

Raise your engine to put the AV plate and hydrofoil even with the bottom of the hull and give it a try. Fine tune your tilt pin setting for best balance between quick planing at low speed and best top end.

 

[jack7771]

Re: cavatation/ motor height

Scrobo --

>So what is a "hole shot"?<

That is the action of powering at full throttle from a forward idle speed to get the boat on plane as quickly as possible. A better hole shot means you get up to plane quicker.

 

[scrobo]

Re: cavatation/ motor height

Oh! I understand now.

Never heard of it referred to as that. being a noob and all. My boat was terrible at getting up to plane. Hoping the smart tabs help. will find out in 4 hours.. heading up north now.

BYE ALL! HAVE GREAT WEEKEND! WISH ME LUCK!

On a side note.. I had a dream last night the boat sank and now I am off fishing up North Hmmmm...