The screw is the device used for ship to go forward and it has the rotating axis with 2 to 6 blades.

Depending on the blade angle and number of the screw, the ship speed differs.

The number of blades differ depending on vibration and the ship size with small ships for 2, military vessel or motor boat for 3, and large ships for 4~6 blades.

The testing screw is made to measure the forwarding speed, propulsion power, rotation number and others to find the optimal screw types for each ship.