Stick with Shaft size for repower?

[CThomps]

My 1986 20ft Aquasport Osprey 200 is gonna need a new motor here soon.  

The current motor is a 1985 mariner 150 with i'm pretty positive a 25" shaft.

Can I get a 20" shafted motor when I repower?  I'd like to repower it with a 115 Mercury 4-stroke if I can find a good used one being that the boat is setup for it and all.

[compcrasher86]

I am not sure about the shaft size but I can tell you that the new Mercury four strokes are extremely heavy. Although your stepping down to 115hp I doubt there is much of a weight difference between that new four stroke and your old 150. Do expect to go a fair amount slower.

[GoneFission]

Go with a 25" shaft - it will stay out of the water much better, and I'm not sure your boat has a transom that works with a 20".  

It's interesting, but some recent tests have not found much difference in mileage between modern injected 2-stokes (HPDI, Optimax, etc.) and the heavier and more expensive 4-strokes.  And the new 2-strokes meet the latest emission standards.  
 

See ya on the water!

[Hardwater]

If the transom is built for a motor with a 25-inch shaft - don't go shorter.  It is possible to go with a longer shaft motor using a setback bracket or jack plate...but not the other way around.

With out a doubt, four stroke motors are heavier than equal HP 2 strokes.  Since you're looking for a late model used 115hp four stroke - here are the weights listed by manufacturers in some of the random catalogs in my file cabinet:

-2004 Mercury Fourstroke 115 EFI - 386 lbs.
-2003 Yamaha F115 4-stroke EFI - 402 lbs.
-2002 Honda BF115 carbed - 496 lbs.
-2003 Suzuki DF115 EFI - 416 lbs.

Manufacturers tend to list the weight for the 20-inch shaft models...so add 8-15 lbs for models with the 25-inch shaft.

I don't have any information on the newer 2-stroke ETECs from BRP but that info shouldn't be hard to find.  The ETEC weight will definitely be lower.

Whether a 115hp will be enough for your '86 Osprey is another question.  I've always liked running at or near the rated max HP on a hull just so the engine doesn't have to work quite as hard...but it does depend on how  the rig will be used.  I'm sure owners of that hull will likely chime in with their thoughts.  I think the 1980s Ospreys - along with the 1970s 22-2s - have some of the best looking  classic lines out there...so good luck whatever you decide.

[compcrasher86]

I agree with you Hardwater in all aspects. Hes right, dont go shorter or else the propeller may not be sticking down enough = bad bad bad. The jack plates are good because you can pull the motor up a couple inches.

As for the E-tecs, they are technically a two stroke and provide the benefits (plus more) of a four stroke. The 2005 115 E-tec is available in both 20 and 25 inch shafts and weighs in at 380 lbs

And as for the lines on the aquasports, my '73 22-2 is right on that list and proud to be there

[CThomps]

I'm pretty positive that the older 20' aquasports actually came with a 115hp motor from the factory.  

Being that so many places in SW Florida are now 25mph year round speed zones it's kinda pointless to have a boat that can haul ass.

I just want the MPG's.  With a 150 on it I'm pretty positive i'm hitting well over 40mph when I want to.  With a 115 I should be at 30-35 i'm guessing.  Most of the time I just get up on a plane anyhow and i'm fine with it.

Thanks for you help guys.  Now i've just got to actually find a decent deal on a motor.