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Help needed with Transom/engine alignment

S

Slimbob

Member
Hi Folks,
Awesome forum you have here. I hope I'm able to contribute somehow.

I have a question about the transom height vs. the engine leg length.

I thought engines came on short (15") or long (20").

My transom is 15" but my engine is 17". Should I raise the engine to compensate?

I can just build up the transome, I think.

Any suggestions would be greatly appreciated.

I have an older 12' Blue Fin aluminum semi V and a 1988 Gamefisher 9.9 hp md# 225.581990


Happy boating!!
Thanks,
Slimbob
 
Kim,
Same engine we are talking about the 9.9 to 15 carb conversion.

1988 Gamefisher md# 225.581990,sn# 1398 as mentioned in original post.


I just measured both yesterday. Top of transome to bottom of keel is 15".
Inside the top clamp (rests on the top of transome) on the mount to the top of the cavitation plate is 17".

Will double check today. But the cavitation plate was ~ 2" below the keel.

I bellieve this causes extra drag in the water. Also, it is very hard to plane the boat. I need to add a lot of weight up front if I am alone in the boat. It will not plane at all without the extra weight.

Granted it is probaby over powered. but it should eventually plane out shouldn't it?


Happy Boating!
Thanks,
Slimbob
 
Sounds like you will need to raise the engine mount two inches so that the cavitation plate is dead level with the bottom most point on the keel at the transom. You many want to consider installing a hydraulic jack plate that will allow you to raise or lower the engine based on circumstances, like navigating around in very shallow water or optimizing performance when on plane. On plane, the cavitation plate should be riding just on top of the water as it is coming off the keel.
 
Chawk_man,
Thanks for the feedback. I think I have it figured out. I will have to replace the plywood on my transome (only 6" high x the width of transome now) and raise the top by 2" as you say. I don't think putting a hydraulic jackplate on a $300 boat will get it. I'm probably going to sell this boat in the spring and buy another in the fall next year. Wifey won't like a second boat in the yard for the winter. Trying to get the most out of my boat and motor now.

Happy Boating!
Thanks again,
Slimbob
 
Last edited:
Think it through. Depending on how your transom is set up, you may be able to scab in a 3/4" thick piece of marine plywood onto the outside (or inside) of the current transom. If that looks like it would work, be sure to seal the additional piece of plywood with Fiberglas or epoxy.
 
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