Sail Boat Propellers

Sail Boat Propellers

Most sailboats that have an inboard motor come with a two blade propeller. This is done so that when the boat is under sail, there is less drag on the boat. This is understandable, you want to sail the boat, not motor. When you motor, the boat may not have the push it needs to motor well with a two blade prop.

To be effective the propeller has to have enough blade area to keep the blade loading at a good rate to provide thrust. When the blade loading is too high for the prop, high cavitation results, and there is a loss of thrust to the boat. This gives the boat poor response in low-speed maneuvering. Blade loading changes with the boat speed and how water flow passes the prop. At low motor speed and high motor speed a two blade prop may not get enough blade loading or it may get too much loading to effectively give the best thrust. At low motor speed, you get poor response and at high speed the boat is sluggish.

Going to a three blade prop of the same width as the two blade prop will increase the effective diameter or blade area by 40% to 50 %. This usually gives better low and high speed performance. Unfortunately, at the same time, the drag on the boat when sailing goes way up.

A feathering propeller or folding propeller can be put on to get the best performance when motoring or sailing. When the motor is pushing the boat the propeller opens and the blades catch water. When sailing, the blades fold-down on themselves and gives much less drag. These props are big dollar items but they give the best results for motoring and sailing.

Picking a two bladed prop or a three bladed prop may come down to how much motoring you do with your boat. If you mostly motor, go with a three bladed prop. If mostly sailing, go with a feathering prop. When you pick a propeller, either two blade or three blade, pick the correct blade type. They come in sailor blade and standard blade types. Sailor blades are not as wide as the standard blade and give less drag when under sail.