Each outboard boat has its own optimum propeller. But in the case of using the boat in many ways - for fishing, for walking, for towing water skiers - you need a few screws. Be sure to purchase a spare propeller with a propeller mounting kit for your boat.
- - ship;
- - boat motor;
- - propeller screw;
- - tachometer.
Determine the main parameters of the propeller for the outboard motor. They are the diameter of the screw itself and its pitch. The maximum speed of the boat depends on these parameters, taking into account the engine power. The distance in inches the propeller travels in one revolution is the propeller pitch of the outboard motor.
Find in the designation on the propeller itself the diameter and pitch of the propeller. For example, the inscription 9, 9x13 means that this propeller for an outboard motor O is 9.9 inches at a pitch of 13 inches
Look in the instructions for the outboard motor, what maximum speed it can develop at "full throttle", with an open throttle. Accelerate the boat to maximum speed. Use a tachometer to measure the rotational speed of the engine shaft, usually it does not exceed 5500 rpm.
Pay attention to the speed of rotation of the shaft at the maximum open damper. If it is less than the recommended maximum revolutions, then denote the readings of the tachometer as the maximum speed of this type of propeller.
Calculate the propeller pitch of the outboard motor. One inch of propeller pitch is approximately 200 rpm. Find the difference between the tachometer readings and the passport maximum revolutions, divide it by 200. Divide the resulting value by the gear ratio of the outboard motor gearbox. If you end up with a 2, then it is better to use a different propeller with 2 inches less pitch for this outboard motor. With the new propeller, your boat will reach its planned maximum speed
When choosing a propeller for an outboard motor, follow a certain rule. Use propellers with a large pitch for fast light boats, and with a smaller pitch for slow and heavy boats. Changing the propeller pitch of the outboard motor is the only way to match the propeller with the engine and with the boat.