REPLACING A STANDARD SHAFT OUTBOARD WITH A LONGSHAFT

[chippyray]

Hello I have a chance to buy a 90hp longshaft outboard for the right money. The problem is my boats transom is set for a standard shaft motor. I have at the moment a 50hp unit. Will it make any difference as to the shaft lenght for power ect.Will I be wasting the extra power. Will the handling be affected. The longshaft is only 2 ins longer from transom bracket to cavitation plate. Any thoughts?

 

[jfm]

The extra length in the leg will cause more drag and slow you down a good 5 knots or so. On a very fast boat you want the engine cavitation plate an inch or 2 above the bottom of the hull.

Simple answer is just bolt the 90hp on a bit higher. Put a 3inch bit of timber on the top edge of the transom and lower the motor onto that, then bolt it.

Of course, you need to be sure there are enough bolts drilled through sound transom. The top bolts might not work in this arrangement. If it isn't strong enough then built up the transom with a plywood+GRP extension to the top edge

Or you could buy a proprietary outboard jack-up plate. These cost big £££ for the hydraulic lifters, but less for the bolted ones.

How big is the boat? I'm guessing smallish boat and now massive outboard. You probly want to bolt the engine off centreline, praps 1.25 inches tot he starboard side, to counter the prop torque and balance up the steering (assuming a r/h turning prop)