Zanshin I Gori folding Propeller

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Gori folding propeller Freshly greased and scraped Gori folding propeller on Zanshin I in preparation for the boat being splashed at Nanny Cay in the BVI.
(2008-12-18 19:35:41 DSC-N2 [f/4.0, 10/2500s] ISO 160)
Gori folding propeller
Zanshin I's Gori prop The Gori folding propeller on Zanshin I in a folded state while on the hard at Nanny Cay in the BVI.
Zanshin I's Gori prop
Gori folding propellor Here I've used axle grease liberally around the gearing of the Gori folding propellor. I should have cleaned thoroughly but didn't have sufficient time before Zanshin I was scheduled to be put back into the water.

[18°24'1.39"N 64°38'1.51"W ]
Gori folding propellor

Most sailboat propellers are fixed, with 2, 3 and sometimes even 4 blades. The advantage of a folding propeller is that when it isn't being used for propulsion it folds together and thus decreases the boat's drag substantially; this can make a difference of a knot in boat speed - while just over 1 mph doesn't sound like much on a highway or the Autobahn, when a boat's top speed is 9knots it suddenly becomes a more interesting number - 10% speed increase sounds a lot more significant than a mere 1 nautical mile per hour. The downside of a folding propeller is that (a) it is very expensive and (b) it is mechanical and as such is prone to developing a problem. In the boating world, it is a well-known natural law that the odds of a piece of equipment breaking down is proportional the at least the square (if not the 3rd power) of the distance from the nearest service facility. This means that the propeller, if it decides to break, won't do so at the dock in St. Martin but it will patiently and cunningly wait until you have arrived at Vanuatu or some even more remote location.

The Gori folding propeller has one other very nice feature, it has a so-called “overdrive” or “cruising” mode. This allows the boat to motor sail (use both sail and engine power simultaneously) using much less fuel than normal by using the reversing pitch angle while going forward. This is easy to set, just motor slowly backwards and then shift from reverse to neutral while the boat is still moving backwards, then into forward; by doing it this way the blades are still in backwards mode and the movement of water over the propeller keeps it from shifting into “forward” pitch angle. The reverse pitch is flatter, which will produce the same forward speed at lower revolutions (or engine RPM's) than normal. This is a similar effect to choosing a higher gear in a car, but the downside here is that it is possible to over pitch and thus overheat the diesel engine. I've managed this once and will be much more careful with my settings in the future.

Downloadable Manuals page - Gori folding propeller Manuals

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