Longshaft motor on short-transom boat (not a grady)

[timo14]

I posted this on THT a while back, but i only got a few responses. I'm hoping a fellow GW'er will help me out even though this is not a GW question. Here goes:

I have a 1964 SeaKing and want to put a longshaft 9.9hp 1986 Mercury on it (I think it's actuall an XL shaft). In short, I've owned the motor since new and it's in fantastic shape... the boat was basically free. I got it to fish some flats & rocks that I frequent. The boat is going to get beat pretty bad, so I'm trying to keep it relatively cheap. So, my thoughts are to put a new transom on the boat that sticks up above the original transom height to make the long-shaft sit at the proper height. Make sense? So, could someone help me with the height? Here are a couple of photo's.

Looks kinda silly...

The top of the tape measure is flush with the keel in this photo... so the cav plate is 8" below the keel.

The only advice i got on THT that made sense is to move it up 5". Moving it up 8" would put the cav plate flush with the keel. But, the advice i was given said that small HP outboards are supposed to have the cav plate 3" below the keel. This seemed reasonable... just want to confirm before i fabricate the new transom.

Thanks,
Tim

 

[Curmudgeon]

Measure from the cavitation plate to the bottom of the hull. Makes no sense unless you're gonna jack it that far. The engine will lug (not good) and kill any performance the boat might have had ... :cry:

 

[timo14]

I am going to raise the engine. What I'm trying to figure out is how far to raise it. Where should the cav plate be relative to the keel?

 

[Amigo]

http://www.themarinedoctor.com

Go here to the Mercury section. I'm sure they will have an answer for you.

 

[JUST-IN-TIME]

got to raise that thing far!

 

[gradyfish22]

The planing flat on the outboard that is just above the propr should run parallel to the bottom of the hull, that is roughly the correct position for an outboard. To get the best results , sometimes bumping it up or down an inch will be better but for that boat it wont make much of a difference in performance, but that is a good way to judge the correct height.