Hi Thrust Prop on an outboard
I installed a high thrust prop on my Nissan 9.8 outboard which powers my Cal 28 and here's what I noticed:
-One big feature of this high thrust prop is the bigger collar which holds the blades. This allows the exhaust gases to escape out the back normally when going forward, or to escape out the front of the prop when going in reverse, eliminating any cavitating when going in reverse (from exhaust bubbles going back through the prop). The old prop didn't have nearly the bite in reverse that this prop does, and when you're heading toward the dock too fast and put it in reverse and rev it a bit, the motor doesn't race unpredictably as it did with the normal prop.
-The reduced pitch gives more resolution to the throttle at low speed. With the normal 8.5 pitch high speed prop, if you idled in forward, it would still propel the boat around 2 knots, which can be uncomfortably fast when docking, forcing me to take it in and out of gear when approaching the dock. This prop at idle pushes the boat forward around a knot, which is much nicer.
-I got the 7 pitch 4 bladed prop, which has definitely raised the RPM of the outboard at WOT. I don't have a tach, but the high speed prop seemed to bog down the motor at WOT and it seemed the motor was straining a bit. From some preliminary tests, it looks like it will give a bit over .3 knots of an increase in speed, though I haven't tried it in calm water at slack tide yet. The high speed prop would push the boat around 4.9-5.0 knots.
-This particular prop (sold by Nissan) is much thicker than the high speed prop. Hopefully it will last longer and be more forgiving than the much thinner high speed prop.
So to those with outboards thinking of trying out a high thrust prop, it may be worth a try.