Re: Minimum hp for my boat??
The rule of thumb I've heard the most is 70% of the max hp rating. (Which sort of agrees with the 75% rule stated above). In your case, 70% of 140 is 98 (140 x 0.7).
I'll tell you of a similar experience that would closely relate to you putting a 50 on that boat. A few years ago I picked up a 1973 15.5' Crestliner tri-hull, rated for 80 hp, that had a '93 Johnson 40 on it. Basically it was a useless package. With only me and a fishing rod on it, it got up onto plane pretty easily and topped out at 28 mph. With no spotter on board it would pull a small tube with a lady on it. Not bad. Put two guys in it (and consequently a couple coolers) and it would barely get onto plane and probably hit 20 mph. That was making the motor work as hard as it could with it obviously burning a lot of fuel.
Put a third person on OR lots of fishing gear, the dog, a third cooler for food and it wouldn't plane at all. At that point, you're rocking at displacement speed so you may as well have an 8 horse on the back. In fact, an 8 horse would have been better since the 40 was louder, harder on gas, and at idle it was still too fast for trolling.
Anyway, that was at 50% of max power. A fifty in your case would bring you to a little under 36%. If you're investing what I consider serious coin on a motor, I wouldn't risk total disappointment by ending up with a majorly underpowered boat.
LC.
PS. Late-90s and up JohnnyRude V4s are remarkebly quiet. My 2000 Johnson 90 (which ironically has since blown up) was arguably quieter at idle than my 1990 Evinrude 9.9.)
