You will need
  • - the ship;
  • - motor boat;
  • - thruster;
  • - tachometer.
Define the basic parameters of a propellerfor a boat motor. They are the diameter of the screwand its pitch. From these parameters, given motor power depends on the maximum speed of the boat. The distance in inches traveled by the screw ofω in one revolution, there is the step screwand the boat motor.
Find it in the symbol marked on the heart of the rowing screw, the diameter and the value of the step screw. For example, the label 9,9h13 means that the propellerand outboard motor O is 9.9 inches when the step is 13 inches.
View the instructions for boat motor, what maximum speed it can develop into "full throttle" when the throttle of the throttle. Accelerate the boat to maximum speed. A tachometer measure the speed of rotation of the motor shaft, usually it does not exceed 5500 rpm./min.
Note the shaft speed at the maximum throttle. If it is less than the maximum recommended revs, the readings of the tachometer indicate the maximum speed of this type of propeller screw.
Calculate the step screwand the boat motor. One inch step screwand is approximately 200 rpm./min. Find the difference between the tachometer readings and the maximum nameplate rpm, divide it by 200. The resulting value divide by the gear ratio of the boat motor. If in the end you will get figure 2, therefore, for this boat motor is better to use a different propeller screwwith step 2 inches less. With the new screwom your vessel will achieve the planned maximum speed.
When you select the screwand to the boat motor stick to certain rules. Screws propeller with a large pitch for high-speed use light boats, and smaller increments for low-speed and heavy. Variation of the pitch of the propellerand the boat engine is the only way to align the screw with the engine and the boat.