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Propellers & Rudders
When choosing a propeller, those variables must be considered: diameter, that is its size; pitch: the inclination of props blades, which determines the theoretical forward movement the propeller makes at each rotation; number of blades: normally 2 or 3 on RC boats, although there are special props for submarines with 5 or more blades; shaft diameter: The most common sizes are 3/16 (.187") and 1/4 (.250"). Besides that, we must take in considerations whether the prop will be used in a surface drive configuration wherever the prop will be used at the surface - a situation where half prop is under water and half out of water - or subsurface, in which the whole prop is under water. The first type - surface drive - gives better performance and for that reason is used on boats where performance is the prime requirement.. Because of the vast variety of types, sizes, dimensions and materials of props commercially available please contact Cast Your Anchor and talk to our technicians. Except for sail boats, all boats need a system that transmits power from the engine to the propeller. On outboards, this transmission is inside the engine and is not visible. What you see is a cylinder, much like that of an airplane motor, normally wrapped by a water jacket - although some of the more moderns engines are using air cooling - and a lower end with a propeller on top . Inside, a flex cable links the motor crankshaft to the prop. For all other engines, internally mounted in the hull, some kind of transmission must be made between the engine and propeller. Mostly used types are the rigid shaft , which demands 1 or more u-joints to allow for the inclined angle from the engine to the propeller shaft, parallel to the bottom of the hull. This kind of transmission is normally limited to electric boats or glow engines with low HP. and comes with kits for assembling this kind of boats. For engines with higher HP and for gas engines, the transmission is via a flexible cable that looks like the speedometer cable of your car, but much more larger and stronger. This "flex shaft" runs through, and is supported by a brass tube with or without a teflon liner. This tube can be bent to create the correct angle from the engine and become parallel to the bottom of the boat, linking to the prop axle. One of the tips of the flex cable links to the engine crankshaft by means of a special coupler screwed onto the engine crankshaft on one side and with a square hole on the other side in which fits the flex cable. Once again please contact one of our technicians at Cast Your Anchor to get the proper specifications for your project.
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