Jack Plate Installation

[Crestliner2007]

Earlier in 2007 I posted about a top end speed problem (lost speed) I was having with my 15 hp Yamaha, once I installed a Doel Fin on the cavitation plate. From the feed back here, I've purchased a "Mini Jacker" jackplate to attach to my transom; in order to give me the adjustment I'll need in raising the engine. My goal is to get the Doel Fin to just break the surface of the water at top end, while not exceeding max. rpm's. Now my problem: The instructions say to use six (6) bolts in the jackplate to attach to the transom. OK. But, I won't know the exact position - height - to install it until I put it on and try it; then re-position and try it, etc.. I've purchased a "Tiny Tach" tachometer with which I'll also monitor top end rpm's - to make sure I don't exceed mfg. specs. So, now I have the tools. How do I go about attaching the jackplate "temporarily" to my transom (so the engine doesn't go for a swim!)? I was thinking about a pair of large C-clamps? Not sure if this is practical or safe? Or, should I drill just one bolt hole on each side for the trials? I have plenty of hole positions available to me on the jackplate, so it's just the transom I'm concerned about. I'll use the engines turn screws to attach to the jackplace until I find the correct height. Thanks for your input!

 

[EJ3]

Re: Jack Plate Installation

I have never done anything with a jackplate, but here's what I think...

Attaching your OB to your transom with a less than adequite setup is a bad idea (ie c-clamps). I would find the middle adjustment on the jackplate, that way you would have the same amount of travel available for up as down. Measure from the cavitation plate to the first bolt hole on your OB. From the bottom of the transome, measure up that same distance and that is where the bottom holes on the jackplate should be when mounted.

What I am trying to accomplish is having just a much travel for up as down when the cavitation plate is even with the bottom of the boat.

I am not sure that is right, but the experts will chime in soon!!!

Good luck!

 

[tashasdaddy]

Re: Jack Plate Installation

this is my jack plate i made for my 40 hp. the av plate needs to be even or above the straight line of the keel. i have a short shaft transom with a long shaft motor, i calculated how much i need to raise the motor, then postioned the brackets, then mounted the plywood, to the exact height i needed. works beautifully.

 

[Silvertip]

Re: Jack Plate Installation

Hey Tash -- did you know your transom has "measles".

 

[Crestliner2007]

Re: Jack Plate Installation

Thanks for the input guys! Looks to me like this is going to be a tougher project than I originally expected.

 

[boatmanjf]

Re: Jack Plate Installation

A doel-fin wil cost you a few on the top end. It alows you quick hole shot but you loose it at the top speed.
With the instalation of a jack plate you will not need the doel-fin...I would remove it. The jackplate should be placed dead center of your transom hieght. Start adjustment with cavitation plate (with fin removed) even with the bottom of the keel. You will see a better perormance from there before you even start fine tunning. As you raise the engine a little at a time. Be VERY awair of water intake. Many bass boats have burnned up motors for trying to raise them too high. The higher you go the faster the boat gets.

GOOD LUCK.

P.S. Your boat is not too unlike mine. 93 SmokerCraft Pro-Alaskan 19' (with 10" jack plate)