Go with a high thrust four stroke in the 8 to 9.9 range.Yamaha and Honda both produce high thrust kicker motors that are specifically made to push heavy loads like sail boats.
They are awesome kicker motors for trolling and as a back up in an emergency.
I currently have two Yamaha kickers.One is a 9.9 Yamaha high thrust four stroke.It's on my 22' Trophy and is used exclusively for great lakes salmon trolling.
It will push this boat(5,000lbs with people and gear)to about 5.5 to 6 MPH.
It runs for at least ten continuous hours at a time,and never misses a beat.
The other engine is a Yamaha 8hp high thrust with power trim and tilt/electric start.It's mounted on my 23 Tsunami project,and will be pushing this boat in the fall.
I have no doubts that it will do none other than a fine job.
Both of these are connected to the outdrive via an EZ-Steer connector rod.You can hook the kicker to an outboard with the same connector system.
Oh yeah,they both are long shaft(20")motors.
Following is a picture of my new 8hp kicker setup on my SeaCraft Tsunami project.
Hope this helps some.
