Greetings and welcome aboard the CF, Scott.
According to Cliff Friesen, of West by North Enterprises (makers of “Campbell Sailer” propellers)
Two Blade Fixed Blade Propellers
This old belief is the main reason not to go with a two-blade propeller
. Two-blade propellers do not belong on a sailboat.
(Very personal opinion) Disturbed water
is the main reason. Every keel
has disturbed water
coming off of it, be it a streamlined fin keel
or a full keel. Water meeting on the trailing edge takes time for the flow to smooth out. Two-bladed propellers turning, go through the disturbed water at the same time. This causes a slippage, in turn inefficiencies because it is on/off/on/off etc.
How many skippers with two blade propellers notice the stovetop, lifelines
or something else humming, at different engine rpm
? How many blamed the engine
? This is usually caused by the harmonics set up by the two-blade propeller
. Sometimes in combination with the harmonics of the engine, it can cause even more uncomfortable zones in engine rpm
You also get turbulence created by the over sized propeller. It is oversized to compensate for its lack of efficiency, usually in pitch
. The pitch
directs water to the other side of the keel or propeller. This happens at the top and bottom blade when vertical behind the keel or strut. This causes turbulence and thus drag with the exception of the very small inefficient propellers.
Three Blade Fixed Propellers
A three blade propeller is the better way to go.
You only have one blade moving through the disturbed water at any time. Two blades are still pushing the boat
. We have more efficiency, more thrust, more control and less vibration. Depending on the propeller mind you it may cause slightly more drag. For some propellers it is the equivalent of dragging a hand through the water. Most sailboat builders use, as the standard fare, heavens forbid, a powerboat propeller and the drag can be much worse, like dragging a bucket. At best, in order to cut drag, some propeller manufacturers cut down a powerboat propeller to make it have less blade area, loosing the majority of its thrust and ability to control the boat. To compensate, they increase its size either in diameter or pitch. It is quite common to have more drag with a standard two-blade powerboat style propeller than a properly designed sailboat three-blade propeller. A properly designed sail boat propeller will give the vessel good thrust in forward and reverse from minimal horsepower engines and offer low drag when sailing. There are patented sailboat propellers with low blade area (read less drag) that have, through design, maintained and exceeded thrust figures compared to standard style propellers. An added benefit or disadvantage is that they can often reduce the prop walk in reverse. Most skippers like to be able to back in a straight line. Many skippers like the simplicity of a fixed propeller along with its lower price