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Author Topic:   Long-shaft / short transom
chrisc posted 06-16-2001 10:45 PM ET (US)   Profile for chrisc   Send Email to chrisc  
I'm thinking of buying a 13ft Classic equipped with a 30hp '97 Evinrude. I noticed that the transom is 15", not 20" as in later models. The motor, however, appears to be a long-shaft. Are there any known problems with this configuration?
dfmcintyre posted 06-17-2001 08:31 AM ET (US)     Profile for dfmcintyre  Send Email to dfmcintyre     
Chris -

I've got that same situation with my 21' Outrage, i.e. long shaft bolted to a short transom.

No problems, aside from a reduction in predicted top speed.

Right now, we're looking at a manual, but adjustable bracket, but in my opinion, it would be overkill to bracket a 13'.


chrisc posted 06-17-2001 02:54 PM ET (US)     Profile for chrisc  Send Email to chrisc     
Thanks for the input Don. One thing I forgot to mention is the motor has a stabilizer attached mounted to the anti-cavitation plate. Could this be an attempt to counteract any porpoising that might be caused by the shaft being too long?

-- Chris

bigz posted 06-17-2001 04:00 PM ET (US)     Profile for bigz    

Don is being kind on reduced performance! Though I was under the impression the 21 outrage handled a 20", anyway the effect will be multiplied on a 13.

Might suggest an inexpensive way to solve the problem is with a a set back plate made by CMC basically has 5" of slot adjustment at the motor mounting bracket and 1-1/2" of adjustment at the transom bracket. Available in 5-1/2 or 4 inch set-back. suggested retail is $157

Actually I run a 5" Bob Machine Shop jackplate on our 13 with a 35 hp Force 15" shaft, we do have trim and tilt which also helps performance.


chrisc posted 06-17-2001 04:27 PM ET (US)     Profile for chrisc  Send Email to chrisc     
Thanks Tom. Ok, here's the next logical question. How difficult is it to mount a setback plate, and what precautions need to be taken in doing so?

-- Chris

Bigshot posted 06-18-2001 11:07 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
That long shaft on a short transom(i assume a blue interior, all whites are 20), will put a LOT of stress on the transom and really hurt performance. Imagine driving 30mph with your arm in the water 6 inches, impossible right? Try moving it down another 5 inches. I would walk a way from it if you are sure it is too long. The cavitation plate should be about level with the hull bottom. It is not good to do that.
bigz posted 06-18-2001 12:42 PM ET (US)     Profile for bigz    

You probably will have to fill in the original mounting holes and drill new ones.

The plate comes with good installation instructions.

I would use the full 1-1/2" on the transom side, then you can play with positioning using the 5-1/2" on the motor side.

Cook also makes just height increasing rails which maybe all you really need.

Now here is a couple of 13 Alert photos with a 10" jackplate --- hmmm maybe a tad much then again --- anyway your concern is to get that motor raised properly so as not to impair performance --- if the boat and the motor is in good shape the price is fair go for it ---

Steve Leone posted 06-26-2001 07:20 PM ET (US)     Profile for Steve Leone  Send Email to Steve Leone     
It is possible to mount the engine higher on the existing transom without the use of a "jack plate". Most outboard motors come with a multiple choice of mounting holes. I mounted a 40hp Yamaha with a 20in. shaft on a 13 whaler with a 15in. transom this way with no ill effects. You can do this with or without a block between the bracket and the transom. Always use the proper stainless hardware and be sure to seal the holes with sikaflex. Good day, Steve.
Bigshot posted 06-27-2001 10:24 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
You can raise a motor off the transom but not 5 inches.
Steve Leone posted 06-27-2001 12:18 PM ET (US)     Profile for Steve Leone  Send Email to Steve Leone     
Actually 4in. which is pretty darn close. This was with the 40 Yamaha. I believe O.M.C. products are capable of the same. Not sure about Merc though, Steve.
Bigshot posted 06-27-2001 02:36 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I know they have 4 inches of adj within the bolt holes but you can't mount an engine 4 inches above the transom top, The top bolts would not be bolted.
lhg posted 06-27-2001 03:28 PM ET (US)     Profile for lhg    
Larger Mercury engines, and most engines, since I think this is an industry standard, have 5 bolt holes, with 3/4" centerlines. This allows a maximum height increase of 3",
and is not enough to mount the next longest shaft length engine. You'd still be 2" too low. So CMC static lift plates, or a setback transom jack, are required.

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