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Old 03-28-2002
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Reducing Propwalk

I have a 28-foot O'Day sloop. I have been told that a three-bladed prop will reduce propwalk and provide more speed when under power. Is this true? If so how do I replace the prop?

Mark Matthews responds:
Propwalk results from an imbalance in forces. Imagine your propeller spinning. When the propeller spins, the blade at the bottom of the circle moves through deeper water at higher pressure and creates more thrust and transverse force than the blade at the top of the circle. This pushes the shaft slightly sideways, resulting in unbalanced handling, which can be particularly nettlesome in reverse.

Generally speaking, propwalk is more pronounced at lower speeds than it is at higher speeds when the blades are operating with higher efficiency, so you may want to try an extra boost on the throttle. The choice of a propeller depends upon such factors as engine, shaft rpm, boat displacement, and how much stuff you’re carting around. I’d recommend brainstorming with other O'Day 28 owners on our E-mail Discussion List to find out which
pitch and blade combinations have worked for them.

Remember that propellers vary in blade angles, diameter, and pitch. Pitch is measured in inches and is the distance a prop travels forward during a single revolution. Three-bladed props are usually reserved for cruising boats and ordinarily are large diameter and set at a low pitch. And whether you're motoring against strong currents and into headseas or putting along in flat seas will also be factors in the choice of props. In many sailboats, propwalk is just a part of life, and the only ‘fix’ is to know that the boat handles in a certain way so that you'll be prepared for that before you get into a tight spot. However, if you have some cash to burn, you can check out the AVP prop, which automatically adjusts for the right pitch and the right rpm, reducing drag and increasing performance, handling, and fuel efficiency.

Before changing to a three-bladed prop though, consider what kind of sailing you do and how many hours you put on your engine each season. If you’re primarily daysailing in essentially fair conditions and would rather have a performance-oriented outing, I’d stick with the two-bladed prop, as O'Days are relatively light boats and fixed, three-bladed props bring increased drag. You may want to consult your engine manual or a prop shop near you for a more thorough assessment. Replacing the prop isn’t rocket science, and if you’re interested in goofing around on boats as much as we are, I’d recommend checking out Don Casey’s book This Old Boat. Good luck to you.

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