Outboard mounting with a splash well

[johnbottsr]

I am certain this has been asked before and I have probably read a hundred threads on the subject today. However, I must ask,
I have an early '90s Crestliner 216 Phantom SST.
The SST stands for "Space Saving Transom" which I would call a splashwell.
Now, the problem I have is that I get a LOT of splash from the outboard on this boat with the cavitation plate set about at the same level as the bottom of the hull.
I have been contemplating a jack plate to raise the motor up (I am out of adjustment holes).
My question is:
Since the SST (or splashwell) effectively an offset for the outboard, does the "raise the cavitation plate one inch above the bottom of the hull for every 12 inches of offset" rule of thumb apply?

If it does I might just modify the mount for the outboard on the splashwell to account for the offset and not spend the dough on the jackplate.

So let's say the splashwell is 24" (it rides higher than the rest of the boat).
Should the cavitation plate on the outboard be 2" above the bottom of the hull?

Apologies if this is a dumb question.

 

[metriccrescentwrench]

Re: Outboard mounting with a splash well

That "rule" is an old wives tail which doesn't consider hull design or anything. Basically what you want to do is adjust the engine height so that the AV plate is just a bit above the surface when you're running on plane, simple as that.

 

[Frank Acampora]

Re: Outboard mounting with a splash well

Because of the angle the boat rides at, water will "rise" above the bottom of the transom. The further the engine leg is set back from the transom, the greater this apparent "rise." Engines that are set back from the transom can and usually are run higher to account for this. I don't believe there is any set rule, you raise the engine until you get ventilation, then lower it slightly. Hell! most engines can be run about an inch above the bottom with no set back.

 

[johnbottsr]

Re: Outboard mounting with a splash well

The engine is not on a jack plate so adjustments will be more difficult.
Right now it is as high as it can go and I am weighing modifying the transom or buying a jack plate and just want to know if the splashwell would act the same as a setback or is it more like the actual hull?
Just a basic calculation to get in the ballpark so I don't need someone with a measuring stick hanging off the back to see how far up it needs to come.

 

[metriccrescentwrench]

Re: Outboard mounting with a splash well

I am weighing modifying the transom or buying a jack plate

I'd go with adding the jackplate any day of the week. Way way easier..

just want to know if the splashwell would act the same as a setback or is it more like the actual hull? Just a basic calculation to get in the ballpark so I don't need someone with a measuring stick hanging off the back to see how far up it needs to come.

IMO you're over complicating this. Here's what I'd do.... Add a 6" or so jackplate and adjust it so your engine is an inch or two higher than it is right now. Go for a ride with a buddy and take a look at the AV plate, it's not at all difficult to see if it's below the surface or not. If it's still below the surface then just raise the jackplate a half inch, then take her out again and readjust as necessary 'til you get the AV plate up to the surface. You just gotta' be careful not to go too high as you could lose cooling water flow (a pressure gauge is always a good idea when you're playing with setting up a jackplate).

AND, since your engine is already as high as it can go and is too low are you sure you have the right engine for the boat (ex. engine with 25" midsection on a 20" transom).