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Elliot - a Tractor Tug uses one of two power methods - which is either a thing called a Z Drive (a drive system using a screw propeller that can be rotated through 360%) or a VSP (Voith-Schneider Propeller).
The VSP drive is based on a cycloidal propeller made up of a circular rotating plate at the bottom of a ship, from which a number of vertical aero foil type blades project. Each blade changes the angle of thrust as the disc rotates, thereby generating thrust in the right direction.
The actual name of the Tractor Tug comes from the hand operated directional controls, which are similar to the controls used in some agricultural tractors.
In a Tractor Tug the drive units are located approximately one third back from the bow. See Picture 1.
They can go in any direction obviously, hence the round "bridge".
A similar type of Tug is called a RAVE (Robert Allen Voith Escort) Tug - this however has two VSP propulsion unit's. See Picture 2.
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The SD40 is 55 now!
Last edited by Kevin WS; 04-19-2018 at 11:38 PM.
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