The right propeller can determine whether we're back at the club, drinking rum toddies with the boys and girls, or still out there motoring to windward with our egg-beater of a prop churning away, but going nowhere fast. Just because your current prop came with your boat doesn't mean it's the right one for your boat, your engine, or the type of sailing you do. The difference between having just a prop, and having the right prop, can sometimes be dramatic.
Here's a rundown of the main areas of consideration to help determine if you and your prop are made for each other.
Sailors commonly assume that the propeller on their boat must be correctly sized, simply because it's there. This is frequently not true and may be detrimental to your boat's performance. Here's how you determine if your propeller is right for your boat.
Your engine is designed to run under a pre-determined load. A correctly sized propeller allows for clean, efficient acceleration, and yields a specific desired maximum engine rpm at full throttle. This is necessary for the longest possible engine life. The target rpm is specified by the engine manufacturer for each model. It may be stamped on the engine itself, and it is a number you should know.
Types of Propellers There are many different kinds of propellers on the market today. Let's take a look at the advantages and disadvantages of each when choosing the right one for your boat and the type of boating you do.
|Fixed Props The most common propeller you see on sailboats is the fixed type, made of bronze. These are either two or three bladed. The fixed prop has the advantage of being the least expensive. It offers good forward thrust and has no complicated parts that require maintenance. It's easy to put on and take off the boat, especially if you have a prop puller. |
In reverse, however, a fixed prop performs poorly. Since its blades are designed for forward thrust, as much as 50 percent of the thrust is lost when shifted into reverse due to the trailing edge now acting as the leading edge. Also, there is considerable drag from a fixed prop when sailing. On our last boat with a 21-inch, three-bladed prop, we lost one knot of speed when we stopped it from spinning.
Unlike some of the fancier props available, a fixed prop always carries the designation of RH (Right Hand) or LH (Left Hand). A right hand prop spins clockwise when looking forward from the stern, and a LH prop spins counter-clockwise looking forward from the stern. It's this spin that determines which way your transom will "kick," when you put the boat in reverse. A right hand prop kicks left in reverse, and LH kicks right. This "propwalk" has been the demise of many sailors' docking attempts over the years. Once you learn to use "propwalk" to your advantage though, you'll look like a real pro coming into the docks.
Folding Props Those in search of a super-slippery underbody when sailing usually choose a folding prop. The folding prop provides the least amount of drag of all propellers. When the engine is stopped, the blades of a folding prop collapse upon themselves and become very streamlined, with the tips of the blades facing aft. They look like a squid when folded.
Folding props suffer from the same poor thrust in reverse that fixed props do and they are considerably more expensive. In addition, they sometimes fail to open or close properly.
|Feathering Props For the sailor who wants to get where he's going quickly under both power and sail, a feathering prop is the obvious choice. A feathering propeller offers several advantages when compared to a fixed prop. When the engine is shut down, water pressure passing by the blades of a feathering prop causes them to turn and align with the flow of the water, thus reducing drag by up to 85 percent. Certainly this is an advantage to the racing sailor and also the cruising sailor who likes to sail fast on long passages. In reverse, the blades of a feathering prop rotate and provide equal thrust when going either backward or forward. This helps reduce the nasty effects of "propwalk." On our last boat with a feathering prop, Sue used to back into the tightest possible slips with extraordinary ease while I watched women on the dock pounding their husband's shoulder and exclaiming, "Why can't you do that?" |
Some feathering propellers allow you to adjust the pitch of the blades externally while diving, and others require that you haul the boat to make this adjustment. In either event, there is some flexibility in the pitch of a feathering prop. A new type of feathering prop now available, the Autoprop, adjusts the pitch automatically while underway to maximize thrust and minimize fuel consumption.
Although more expensive than a fixed prop, a feathering prop costs no more than a new sail for most boats, and if properly used and well maintained, could last virtually forever.
Sue and I had planned to transfer our feathering prop to our new boat, but unfortunately we found that there was not enough space fore and aft for this type of prop in the enclosed aperture that surrounds the propeller area on Serengeti. This led us to concentrate on getting the perfect fixed prop matched to our boat, with the knowledge it will always be a good spare if we later find another feathering type that fits and will keep us sailing fast.
If you're not getting the performance out of your boat that you would like when you motor, it's time to do some tweaking on something other than those sails. Do the quick check of engine rpms at full throttle. Improved performance may be as simple as replacing your propeller with one that properly matches your boat and your engine. A new fixed prop may be in order, or maybe one of the folding or feathering varieties if you're looking for increased sailing performance. And, if you'd like to experience those joys of backing up with better control in tight situations, you might just want to consider that feathering type.
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