I'm not sure if the M15 has the same transom height as the M17 but I have a Tohatsu 6hp longshaft (20") on my M17. It is attached to the swing type motor mount. 20" works fine. In these shallow waters I don't think I'd want anything more. I don't get any cavitation issues unless there's 3' snot blowing. Joe Seafrog M17 ----- Original Message ----- From: Karen and Smiley To: Montgomery Sailboat Forum Sent: Friday, March 04, 2011 7:02 AM Subject: M_Boats: M 15 transcom heights Would one be better off using a shaft length of 22 inches as found on the Tohatsu 3.5 hp outboard as opposed to the 20 inch high shaft lengths of most long shaft outboards. Additionally from what I am used to on my P21 which I had driven using a 8 hp 2 stroke I felt that I never could get most of the power out of that engine to making Hull speed at about ¾ throttle. So I assumed that 2.5-3.5 hp would be just right for the M15 with 2 hp being maybe a bit shy for those BAD days when you need to boogie from a storm. Thanks What is the trick to re-fueling when you're out in bumpy waters BTW Smiley magoo252@comcast.net _______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats When posting, remember that there is no privacy on the Internet!