115 hp Mercury outboard shaft length

[william haynes]

I have a 1987 115 hp mercury outboard. the motor blew up so I found a good deal on another Mercury except this one has a long shaft instead of a short shaft. It goes on a 18 ft. bass boat. I installed the motor on the boat and it runs great. the only problem is if I start to trim the motor up it starts porposing and I have to lower the motor full down to keep it from porposing. runs great at full throttle but I can't use the trim. I know this boat should have a short shaft but got such a good deal on it couldn't pass it up. Anything I could do to correct this problem? Thanks

 

[GA_Boater]

Most likely a jack plate would work for you. The long shaft motor is sitting 5 inches lower than it should be. This is made for putting a long shaft motor on a short shaft transom.

 

[Chris1956]

Most of the 115HP motors were 20" (longshaft). Is that what you had? There is a listing for an extra long shaft (25") motor. If your midsection and gearcase from the 20" motor are serviceable, you could swap powerheads.

 

[william haynes]

I had a 20 inch shaft. I think you are right. I need a jack plate. Thanks for the help you guys

 

[GA_Boater]

As long as the powerheads are compatible, that's a good idea to look at. ^^^^^^