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I believe the second formula should be HP = disp/1000 x SA/100, not disp/100 x SA/100.
Steve: Sharp eye on the math (as my own calculations show)! Thanks. I will have this corrected in the article.
On the topic of horsepower calculations, the displacement/1,000 x sail area/100 formula does not apply to mutihulls, which are still displacement boats but carry far more sail area. In the absence of a manufacturer’s recommendation, I’d go with at least 2 HP for every 1,000 pounds of displacement. For the Corsair 970 shown above, for example, the 4,800 lb. displacement x 2 HP per 1,000 would call for 9.6 HP (so one of the 9.8 or 9.9 HP models in this guide. As it happens, Corsair dealers usually sell the boat with a 9.9 HP, and the manufacturer’s recommended maximum is 15 HP.
Doug, thanks for an info-packed article. I recently replaced a Tohatsu 6 manual start with a Merc 6 manual start. I could install the 60 pound Tohatsu myself, but had to have a friend help with the 95 pound Merc.
Steve: Thanks for your comment. I take it you mean Merc 9.9 (a two cylinder model that weights about 95 pounds)? Just curious about the model/size of the boat and the performance difference with a 9.9 HP versus 6 HP?
Steve: Thanks for your comment. I take it you mean Merc 9.9 (a two cylinder model that weights about 95 pounds)? Just curious about the model/size of the boat and the performance difference with a 9.9 HP versus 6 HP?