Jack plate on a 9.9

[C_walters]

Have a 1987 Grumman fisherman 14 and a 1988 Johnson 9.9, I’m redoing the transom this weekend and was planing on building a jack plate to help the little motor all it can. I put the motor on the boat for the first time and to my surprise the cavitation plate is dead even to the bottom of the hull. Now I will be looking for a 25hp motor at some point I’m sure, I don’t want to drill a bunch of holes in my new transom when swapping motors, so my question is being the cav plate is even with the bottom of the hull would I gain anything from the jack plate with setting the motor back 3-5”? I figure if I go ahead and build the jackplate to keep this 9.9 where it is just set back then if I find a 25hp I won’t have to drill into my transom again to bolt the engine on.

Long story short I’m trying to see if it would gain anything or be benifical to set the motor back with a jackplate?

 

[turbotodd]

any setback is better than none. The problem lies in the prop. Generally, you can't raise the engine very high (with a 9.9) because the prop isn't really designed to be run close to-or at the surface. To my knowledge, there aren't many props for the 9.9/15 that would allow one to do so. 25? Different story. There's some choppers, cleavers, semi-cleavers, 3 blade, 4 blade, I think I've even seen 2 blade, nose cones, LW pickup......for 25hp motors. Or maybe I didn't look hard enough for the 9.9 stuff.

Have this issue myself with mine. But it's a 25, and the motor likes to be run high, but the prop doesn't. So off to find another prop. 11" is at the top end of the RPM and 12" is going to be about down about 3-400 RPM. May have to send an 11" in for work. Or quit fiddling and just fish. That may be a better option at this point.

I've got a jack plate built in the shop but with it on the boat, the boat won't fit in the garage-and I refuse to leave it sit outside. And the shop's full of Mustang crap.

You're thiniking correctly. If you're going to a 25hp anyway, just throw a jack plate on it, drill the BIA holes for the plate (make sure the jack plate has the standard BIA mounting pattern!), run your 9.9 on it until you're ready for the 25. That way there's only 4 holes...and if your 25hp has the standard BIA bolt pattern, you could theoretically bolt it on using the same 4 holes.

BIA bolt pattern is 12 7/8" between the holes (measured at their centerlines) on the top 2 bolts, and 9 7/8" at the bottom pair, going off of memory.

 

[C_walters]

Thanks for the reply, I plan on building the jackplate with the Dillion racing plans. Having a removable plate on it that the motor holes will be drilled into. So when the time comes to put a bigger motor on I in theory could pull the engine plate off the jack plate, make a new one up and throw the new motor on without having to redrill my transom.

 

[Azoutdoorsman]

This is the one I built. Not slotted because I didn't have access to the mill the weekend I built it. I just have holes every 1 Inch and holes ever .5 inch on the jackplate for the motor bolts.

 

[C_walters]

This is the one I built. Not slotted because I didn't have access to the mill the weekend I built it. I just have holes every 1 Inch and holes ever .5 inch on the jackplate for the motor bolts.

Did you notice any difference? Do you run the motor above the bottom of the transom being set back? I picked up the material (4” aluminum angle) and I’m going to run 2 pieces of plywood for the clamping board so I should be around 5-5.5” of setback.

 

[Azoutdoorsman]

Right now it is about .5 inch high and 4 and 3/8" of set back. I just finished it a couple weeks ago and I believe I am having carb/fuel issues so have not got it back out since cleaning some crud out of my carb. I will be going out Saturday am to run again. My problem on the test run of the jack plate was that I wasn't able to plane out do to low wot rpms but even at the non plane speed it handled much better. I am running a long shaft motor on a 18inch transom