In discussions about yacht power, choice of engines tends to dominate the conversation. But yacht propellers are equally important. Unfortunately, they’re also commonly misunderstood. Here’s a quick tutorial on just what role yacht propellers play, plus a few helpful tips on how to get more from yours.

Propellers 101

Also called a prop, screw or wheel, the propeller translates rotational energy generated by the engine into thrust to maneuver your yacht. The most efficient yacht propellers would have one blade, because that would create the least amount of drag in the water. That’s not feasible, though, since a one-bladed propeller would be unbalanced and cause vibration. Instead, you’ll typically see three-, four- and five-bladed yacht propellers, which are very efficient and don’t require much power to deliver a reasonable amount of thrust.

Here are some common terms associated with yacht propellers:

• Propeller Diameter is the outer circumference of your propeller, measured across the center. Changes in diameter affect the way your yacht carries itself in the water.
• Propeller Pitch is the distance your yacht travels forward in one revolution of the propeller. It controls your engine’s RPMs.
• Propeller Rake is the degree your propeller blades angle perpendicular to the hub. That angle can be negative (leaning toward the boat) or positive (leaning away from the boat).
• Propeller Rotation is the direction your propeller revolves around the shaft. A right-hand propeller turns clockwise (as you view it from the rear of the yacht), a left-hand propeller counterclockwise.

5 Ways to Get More from Yacht Propellers

1. Start with the right propeller diameter and pitch. A distance of 10 percent of the diameter between the edge of your propeller sweep and your hull is ideal. Much closer and you’ll get vibration; much further and you’ll give up efficiency. Likewise, if you have too much propeller pitch, your engine won’t achieve rated RPM, and if you have too little, you’ll forfeit power. Either way, you’re not taking full advantage of your engine’s capability.
2. Keep it clean. Even one barnacle can throw off the performance of your boat. You can coat yacht propellers with products specially formulated to prevent marine growth from bonding to metal surfaces below the water line. (One of the more popular ones is called Propspeed.) Other options include installing a line cutter or using special paint that helps slough off barnacles.
3. Seat it right. A propeller that’s not properly seated could lead to vibration and eventually potential damage to the shaft. Make sure your propeller seats snugly on the tapered surface of the shaft and cinch the propeller nut and jam nut down to the correct torque.
4. Pay attention to your zincs. The zinc anodes on the shaft are there for good reason. They help keep electrolysis, which can vary from harbor to harbor, from eating away at yacht propellers. If your zincs are deteriorated or damaged, it’s time to change them — your propeller could be next.
5. Watch the alignment. A shaft that’s even a few millimeters out of position can result in unwanted propeller vibration. That’s why it’s smart to do a quick alignment check every time you pull your yacht out of the water. Just use a micrometer to verify the trueness or straightness of the shaft.