# 20" shaft on a boat that requires a 15"



## shadrac (Sep 27, 2010)

Hello

Due to some unusual circumstances I ended up with a 14 foot jon boat (it takes a short shaft 15" transom) and a motor that is 20" transom. I was hoping someone could tell me what the draw back to the set up would be? 
thanks
Jim


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## clarkbre (Sep 27, 2010)

The drawback would be:
1) Hitting the bottom of the lake/river/ocean with your skeg due to an extra 5” of motor in the water.
2) The extra 5” of motor in the water would create excessive drag
3) The overall performance would suffer with a lower top speed, poor hole-shot, and harder to plain since the cavitation plate would be nowhere near where it needs to be height-wise (within an inch of the bottom of the boat)

However, there is a solution and here it is:

Build an aluminum transom riser that sandwiches the transom and raises the longshaft motor to the proper height. The performance will improve greatly and you will have more clearance for shallower waters.


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## Truckmechanic (Sep 28, 2010)

Mine actually went faster with a long shaft. What type of motor do you have? You may be able to convert it.


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## Pappy (Sep 28, 2010)

Clark hit the nail on the head. Nothing but parasitic drag and poor performance with that set up. Raise the transom if you plan on keeping the engine.


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## shadrac (Sep 28, 2010)

Truckmechanic: its a 9.9 Mercury from the late 80's 

thanks for the advice guys 
I appreciate all the input


Jim


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## lckstckn2smknbrls (Sep 28, 2010)

This is the TH mini jacker


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## ditchen (Oct 1, 2010)

I'm running a 20" on a 15" transom. I am using CMC jet drive adapters, or also refereed to as 15" to 20" conversion plates $150


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## RiverRunner (Oct 12, 2010)

It took me forever to find a 50 Short shaft. I thought I was gonna have to do some/one of the things mentioned in this thread if I bought a long shaft.


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