Saturday, July 12, 2014

New Propellers

When replacing the propellers back in Grenada, I had consulted with Vetus, Volvo, and used a software program called Propcalc to calculate the best pitch and diameter for the props.  They all said that 17X13 would work fine.  That's 17" diameter by 13" pitch.  Meaning that for every revolution, the prop would progress 13" forward.  The original props from Privilege were 16X11.  So 1" in diameter and 2" in pitch seemed like it would push more water per engine revolution and give an increase in speed.  Wrong.  Don't trust the numbers.

Since 2009 I have been living with overpropping.  At high RPM the engine ran like a diesel truck going up a steep hill.  Blowing black smoke and not doing much on the power curve.  At low RPM, around 2200, decent speed was produced but the engines could never be run-up.

With fixed pitch props they will always turn when sailing.  This is fine but causes extra wear in the transmission, stern tube, and cutlass bearing, and lots of whirring noise.  You can lock the prop by putting a non-running engine in reverse but that costs Tortuguita about 1/2 knot per propeller.  When we were crossing the Pacific, we would lock the starboard prop on the side that we were sleeping on, or the noise would keep you awake.

So it looked like I was going to have to make the investment in new propellers, again.  There are plenty of 'feathering' propellers but I like the idea, design, and simplicity of folding propellers.  You will supposedly gain 1/2 knot by not spinning a fixed prop.  That should be 1 full knot since we have 2 props.  We'll see.

There are really only 2 big brands of folders.  The Gori and the Flexifold.  The Gori is a 2 speed prop that gives you a bigger pitch if needed but I've already seen what happens with operpropping.  The Flexifold is basic, simple in design and costs half that of the Gori.  It also turns out that a 16X11 just barely fits without hitting the rudder.

Our friends on Lightspeed had issues with the Flexifold and returned them for the Gori but I think the design has changed since then.  I chose the Flexifold at $2000 each plus another $400 for shipping to Australia.

I used Permatex Prussian Blue to check the shaft/prop taper and used valve lapping compound to lap the tapers of the prop and shaft to get almost 95% contact on the taper.

The installation was straight forward and I used extra Lock-Tite just to make sure none of the screws came out.

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