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The size and weight of your boat translates into your need for power (thrust) and endurance. The basic rule of thumb for determining the amount of thrust you need is five pounds of thrust for every 200 pounds of weight. Don't forget to include the weight of your boat's contents in the calculation. To be sure that you have enough power, take the boat's estimated weight and add in its maximum weight capacity. A boat that weighs 1,500 pounds, and has a maximum weight capacity of 1,200 pounds would need a motor with 67.5 pounds of thrust. (1,500 lbs. + 1,200 lbs. ÷ 200 = 13.5 x 5= 67.5)