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→Stern Thrusters
Consult your designer about putting an eyebrow fairing in front of the tube, or a scallop behind the tube, to reduce drag. Don’t put fine grids over the openings, as they clog up. Paint the inside of the tunnel with [https://en.wikipedia.org/wiki/Anti-fouling_paint antifouling paint].
Bow thrusters come with either single or twin propellers. Each has its advocates. The efficiency of one versus the other is unclear. Twin propeller designs contra-rotate contrarotate and are more complex. Propellers are usually square-bladed, made of [http://dupont.com/ Dupont] [http://www.dupont.com/products-and-services/plastics-polymers-resins/thermoplastics/brands/delrin-acetal-resin.html Delrin®] or [http://www.dupont.com/products-and-services/plastics-polymers-resins/thermoplastics/brands/zytel-nylon.html Zytel®] plastic, and designed to be efficient in both turning directions.
The thrust required is a function of displacement, waterline length, lateral water resistance, wind on the superstructure, the forward thrust of the stern, and the turning point on the hull (usually the transom). Some manufacturers’ recommendations are given below. Be sure to consult your designer/builder about the appropriate size for your boat.
== Stern Thrusters ==
Stern thrusters are not essential on boats under 60 ft. They let you make a nice show by parking sideways. They are redundant if you have a [[MarineDrives#Hydraulic Z-driveDrive|Z-Drive]]. They should be placed well aft, for example, under the swim platform but keep in mind safety considerations.
David Myers has developed an innovative stern thruster mounted on the rudder. This Variable Angle Stern Thruster (VAST) can double as a get-home drive.<ref>QUEST V A VAST-ly Different Boat, Robert M. Lane, PassageMaker, April 2006</ref>