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Driftwood

Buying a prop

The boat has a prop but I don’t really like it. It’s a folding prop since the previous owner wanted to race the boat and reduce drag. The downside of this is backing up – can hardly do it since the prop essentially stays folded while backing up. That’s why the boat is not backed into the slip where the cockpit entrance can be used. So the problem is, what prop do you buy? This is something that starts as a science and then moves to art.

I could get a folding prop that allows for better reverse. I could go 2 blade, I could go 3 blade. Fixed pitch, controllable pitch, it’s complicated. So what do I do when it’s complicated? I fill out forms. Boat size, hull type, engine, transmission, max rated RPMs, prop clearances. It’s a lot. I also hit the discussion forum and ask around.

A lot of sailors, those dedicated to sailing, will tell you get a 2 blade with a fixed blade. In fact, that’s what the boat was originally setup with. It’s supposed to be cheap (it is) and provide decent performance while having less drag than a 3 blade. But a 3 blade is supposed to give you better control, better performance and reduce vibration. That made me think, just how much drag we talking about?

The United States Performance Handicap Racing Fleet handicaps your boat based on what prop you have. That should give me a pretty good idea! Here it is for my type of shaft:

  • Two bladed solid propeller on an exposed shaft +6 sec/mile
  • Three bladed solid propeller on an exposed shaft +9 sec/mile

So we’re talking about 3 seconds per mile difference? That’s less than an hour over a 1000 miles. I think I can live with that. 3 blade it is.

I’m going with a brand new Campbell Sailer. This is kind of a high tech design:

Referring to the cross section of the blade in our web page under “The Right Stuff” tab. You can see the reverse air foil in the forward side of the blade. This helps to draw the propeller forward with very little of the blade fighting the water that it is trying to push the boat through. On a standard propeller 50% or more of the blade is fighting the water. There is very little pitch in the first third of the blade near the hub, concentrating the pitch on the outer two thirds. The propeller blade design sheds the air bubbles at the hub. By almost eliminating the bubbles from running across the surface of the blade, we have a propeller that is pushing more solid water, instead of compressing air bubbles. Improved efficiency is the result. The outer two thirds of the propeller have progressive pitch, Jim Campbell called this his “ring of power”.

Propses is tricksy.

Propses is tricksy.

The ring of power, yessss, the precious. We wants it, we needs it. Must have the precious. Uhh, oh, sorry, just getting my geek on. Gimme me a minute here.

We take the precious… and we be the master! So bright… so beautiful… ah, Precious.

OK, got that out of my system. Now where were we? Oh yeah…

 

It has much less drag than a regular 3 blade so I think that 3 second per mile “penalty” should be even less than that:

… the CS prop has a narrow blade profile which translates to 35-40% less drag under sail when compared to equivalent models from other manufacturers.

We’re down to well under an hour and a half extra time when sailing over 1000 miles with that baby dragging us down. For a little reference, the distance between Miami, Florida and London, England is 4437 miles. With a this prop that would translate to about an extra 6 hours of sailing. Not too much when you’re crossing a ocean.

We told him to go away… and away he goes, Precious! Gone, gone, gone! Driftwood is free!

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