Ok don’t laugh at the analogy but I have a 26′ sailboat with a Yamaha 9.9 HP outboard. When I turn the engine too much to port the prop would happily chew in to the rudder. (Don’t ask how this is possible…trust me, it happens to every owner of this boat)
Anyway, I fitted a “prop guard” which is essentially a Kort Nozzle. It’s just a stainless steel ring that completely encircles the prop. Mine fits very tightly and there is very little clearance between the prop and the ring. It does its job, in that it completely protects the spinning prop from contacting something it shouldn’t. It also provided an unreal increase in low speed thrust. This engine was never a dog and always had good low speed torque but with this “Kort nozzle” the power went up dramatically and fuel consumption dropped. I can attain hull speed, about 6 knots or so, at 1/3 throttle; before it was 2/3rds to attain the same speed.
When new you could order my sailboat with either an outboard engine or an inboard 9.9hp diesel. I chose the outboard model because it was faster under sail (certainly it couldn’t be because the diesel cost $8,000 more). There is a diesel model in my boat club (I guess he didn’t care about sailing speed or had an extra eight grand). When motoring the diesel owner always just walked away from me on acceleration to hull speed. That is no longer the case. I bury him and we’re both pretty sure that under cruise I’m using less fuel than his diesel. If this wasn’t on a hull that is pretty much limited to 6 or 7 knots, I’m sure as speed increased we’d see a reversal of this performance.
Ok, not sure anyone cares but thought I would share.
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