Long shaft, short transom

Mossy · Post by **Mossy** » Fri Mar 20, 2009 10:04 am

I am looking to "upgrade" from my 20 horse short shaft to a 25. Problem is, I'm only finding used long shafts right now. What kinds of problems am I looking at if I bought a long shaft. I don't really want to build up my transom or install a jack plate. It's a 15 foot aluminum gregor. Thanks

Post by **G-Man** » Fri Mar 20, 2009 10:40 am

Aside from losing several inches in draft, using a long shaft motor where a short shaft should be fitted will most noticeably effect your top end speed. You may also notice steering problems and will have a reduction in fuel economy. I know in the past you could convert a long shaft to a short shaft and vice versa. This entailed swapping out the driveshaft and spacer on the lower unit. You may be able to do the same with a motor you buy. Check with repair and part shops to see if you can acquire the needed items for the conversion.

Mossy · Post by **Mossy** » Fri Mar 20, 2009 1:45 pm

well, I guess I'll just keeping looking and run with what I have. Thanks for the info

clarkbre · Post by **clarkbre** » Fri Mar 20, 2009 6:08 pm

Mossy wrote:I am looking to "upgrade" from my 20 horse short shaft to a 25. Problem is, I'm only finding used long shafts right now. What kinds of problems am I looking at if I bought a long shaft. I don't really want to build up my transom or install a jack plate. It's a 15 foot aluminum gregor. Thanks

Just a question, but, what do you have against building up the transom or installing a jackplate?

I had the same issue when I bought my 16' Lund short transom with a 15 hp long shaft Suzuki. I measured the cavitation plate/keel difference and had a local welding shop build me a riser that raised the engine 6". The difference with and without the riser is like night and day. The boat got up on plain faster, ran smoother, handled better, and my top speed went up 2mph. For $140 and 4 bolts it is by far the best modification I've done to my boat. I can send you pictures and a scale drawing if you'd be interested.

Rollin with Rolland · Post by **Rollin with Rolland** » Fri Mar 20, 2009 6:31 pm

Don't purchase the long shaft for your short transom. Yes, you can build it up, and that would work fine. That is your best bet. If it is an ABSOLUTE screaming deal on the LS, then maybe consider it. Otherwise, pass. Not sure exactly what your intended use is, but if you ever want to be 100% confident in your set-up just purchase the right length motor. The conversion kits are rather spendy, but are an option ($200-500+ depending on year/make ect.) I would just hold out for that perfect SS.....

I have seen plenty of 9-15hp built up transoms, but does it effect performance once you hit the 25hp+ range??

Gisteppo · Post by **Gisteppo** » Fri Mar 20, 2009 10:17 pm

Just keep your eyes peeled for a short shaft. Look on Craigslist daily, they come through portland, seattle, and spokane all the time.

E

Mossy · Post by **Mossy** » Sat Mar 21, 2009 8:30 am

clarkbre wrote:
Mossy wrote:I am looking to "upgrade" from my 20 horse short shaft to a 25. Problem is, I'm only finding used long shafts right now. What kinds of problems am I looking at if I bought a long shaft. I don't really want to build up my transom or install a jack plate. It's a 15 foot aluminum gregor. Thanks
Just a question, but, what do you have against building up the transom or installing a jackplate?

I had the same issue when I bought my 16' Lund short transom with a 15 hp long shaft Suzuki. I measured the cavitation plate/keel difference and had a local welding shop build me a riser that raised the engine 6". The difference with and without the riser is like night and day. The boat got up on plain faster, ran smoother, handled better, and my top speed went up 2mph. For $140 and 4 bolts it is by far the best modification I've done to my boat. I can send you pictures and a scale drawing if you'd be interested.

I don't want to build up the transom because I already have my 20hp and a 7.5hp kicker both short shafts. Sometimes I take my large motor off and just run the 7.5 on really small lakes.

Gisteppo, I've been looking on craigslist religously since january, guess it's going to take a little longer.

Gisteppo · Post by **Gisteppo** » Sat Mar 21, 2009 8:39 am

The issue with running a long shaft on a short transom is that you stick yourself with huge amounts of drive leg in the water. Only the cav plate and parts below are hydrodynamically smooth enough to actually perform well. Dragging all that extra leg will actually make the boat slower at speed than it is with the existing motor.

Another option is a small bracket/jackplate setup where you can elevate the plate the needed 4", and possibly add trim and tilt to boot.

Bob's Machine makes this one for up to 40hp:

And TsG custom makes this:

http://tsgcustom.com/JsckPlate.aspx

Thats a viable option because you can raise and lower it, plus you get a little performance enhancing setback as well.

E

Post by **AdsBot [Google]** » Wed Apr 08, 2009 7:00 pm

Long shaft short transom - that is pretty funny. If I only had the problem instead of a short shaft long transom! :colors:

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