What if the propeller could choose its own pitch?

Here’s an interesting engineering problem. A conventional fixed-pitch propeller has to work in all sorts of conditions: leaving the marina, cruising under power, pushing into a head sea and motor-sailing. It does all of that with one pitch. But the load isn’t the same in any two of those conditions.

So what if the propeller could adapt?

That’s the idea behind the Bruntons Autoprop. Instead of locking the blades at one pitch, the Autoprop lets them find their own. Centrifugal and hydrodynamic forces on the blades settle them at the right angle for the power and rpm the engine is delivering at that moment.

At cruising speed, the propeller can produce the thrust you need at lower engine rpm, which means less fuel. In the October issue of Latitudes & Attitudes, Bruntons reports fuel savings of as much as 20 percent.

My favorite example is motor-sailing. You’re motoring along, the breeze fills in and you unfurl the genoa. Now the sails are helping drive the boat. With a fixed-pitch propeller, keeping up with that extra speed means pushing the engine rpm higher. The self-pitching propeller simply increases its pitch as the sails add their drive. It adapts to the new condition.

At low speed the opposite characteristic helps. The fine pitch used when maneuvering virtually eliminates prop walk, and the blade’s leading edge presents correctly in both forward and reverse. Shut down the engine and sail, and the blades move into a low-drag position.

Is it the right propeller for everyone? No. If you race and every fraction of a knot under sail matters most, a folding propeller may suit you better. If you cruise, motor-sail and spend real hours under power, it deserves a serious look.

That’s what I find interesting about self-pitching propellers as a naval architect. It isn’t simply about making the boat faster. It’s about matching the propeller more closely to what the boat is actually doing.

Come and see us at the Annapolis Sailboat Show, Booth YB3, City Dock, October 15–18. Tell me your engine model and I’ll size your propeller while you’re there. You’ll walk away with your sizing and show pricing on a postcard. No numbers needed: just know your boat and how you use her.

Next: that noise from the aft cabin may be trying to tell you something.

#SailboatPropellers #Autoprop #Cruising #AnnapolisBoatShow