Outboard on P-19

james nolan (nolan_laboratories@email.msn.com)
Mon, 9 Aug 1999 20:46:49 -0600

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West Wight Potter Website at URL
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All this talk about trailing the P-19 with the outboard has me worried. I'm
not too worried about the weight of the motor lifting the rear wheels of the
towing vehicle off of the ground because you can still steer and brake with
the front wheels making contact. What really worries me is if you put the
whole thing in the water, lower the motor mount and actually start it. The
numbers don't look good: besides the weight of the motor, the moment arm of
the motor mount increases the motor gravitational torque against the hull by
a factor of 2-3 when lowered. The problems are only beginning. Suppose you
start the motor. 4 hp translates into about 200 lbs of thrust which is a 4-5
g force of the motor. Since the driving force (propeller) is off center from
the motor mount there is additional torque (over 200 ft lbs) in vector
addition to the gravity induced torque. Now you add some chop and the motor
is going up and down, so at full throttle in chop you can have much greater
than 6 g motor forces on the transom. Add the entrainment effects of the
water on the motor and I'm really worried. If the transom tears off the
boat, all those pieces of styrofoam will come out and it won't float like
the brochure. Even worse is if the motor propels itself through the transom
into the cabin. I'm at a crossroads for an effective solution. Should I
build a second inner bulkhead to act as a transom when the real transom is
compromised? Should I install a net to catch the motor as it chops its weigh
through the boat? Would a safety cutoff switch on the motor be more helpful?
Would putting the boat on the trailer backwards reduce the effect when
towing? (I've tried sideways a few times, but this has its own problems).

Jim Nolan P-15 #1055, P-19 #426, L138T, LGYC #6