Join Date: May 2007
Location: Glen Cove, NY
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Re: Boat thrust calculator?
Not sure why you think you need thrust. Note that the propeller thrust will equal the hull drag, and as others have said, this is very complex and is not something you can calculate by just plugging into a simple formula. And the BIG variable is the prop. Sailboat propeller efficiencies are pretty low, many in the vicinity of about 50%.
You are better off using one of the rules of thumb to estimate horsepower and then get help selecting a prop that matches your installation. I'm guessing a fixed 3-blade will be the most efficient, but will hurt your sailing performance.
If you really want a thrust estimate, the following from high school physics (well maybe freshman college statics) could be used:
Power = (Thrust x Speed)/33,000
Power would be the engine horsepower at that operating point times propeller efficiency and speed would be in feet/minute. The thrust will be in lbs.
S/V First Tracks
1985 Cal 33-2