Inward or outward turning propellers

[kevd]

What are the benefits or disadvantages between Inwardly turning and outwardly turning props on twin shaftline ships?

What direction do props turn on four shafted ships?

Thanks

 

[oxilume]

kevd,

Are you familar with twist and hogging?

When you twist a large ship, or attempt to turn on a central axis or the ship's CG, the principal is similar to skid steering. However, it differs dramatically in that you can use another principal known as "walking" to walk the stern of the ship to the dock.

All of this depends upon what type of engine is powering the ship. If it is a gas turbine engine, then walking is difficult because each individual shaft always turns in its design rotational direction (either CW or CCW). For Naval Gas Turbine Powered Ships the shaft always rotates in the same direction. So to go from "Ahead" to "Back" the propeller is pitched or inclined backwards via hydraulics to provide "back" thurst.

Now with a conventional engine that has a transmission that can rotate the shaft in the opposite direction, then this is where "walking" comes into play. If you are going to twist to port (turn left), then you would order up:
(1) Left Full Rudder
(2) Starboard Engine Ahead Full
(3) Port Engine Back Full

This will kick the stern (back end) of the ship to the right. So then the port (left) shaft would have to rotate in a direction that would allow the port propeller to act as a tire/wheel if it were in very shallow water. So, the port shaft would rotate CW as would the starboard shaft.

When you are viewing a ship from the stern, looking straight at the propellers, the right screw (propeller) should turn CW and the left screw should turn CCW. This prevents a ship from hogging too much when at full speed or "Ahead" Flank 3.



Todd

http://www.oxilume.com

 

[oxilume]

kevd,

I checked in my old Naval Books and I was wrong about the rotation of the twin screw ship. Port screw turns clockwise and starboard turns counterclockwise.

Todd

http://www.oxilume.com