Parts of a boat propellor
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Short tutorial on Part of a Boat Propeller, Boat Propeller Anatomy, Pitch, Rake, Diameter, Cupping.
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Parts of a boat propellor
- 2. WWW.MARINE-EDUCATION.CO.UK PROPELLER ANATOMY ▸ Blade Face = Confusingly this is the face that faces aft (backwards) i.e. away from the boat. It is the ‘pressure’ side of the blade ▸ Blade Back = This is the face that faces forward i.e. towards the stern of your boat). It is the first part of the prop to meet the water in each turn and is the ‘suction’ or negative pressure side of the blade.
- 3. WWW.MARINE-EDUCATION.CO.UK PROPELLER ANATOMY ▸ Outer Hub = Barrel of the prop that the blades are attached to ▸ Inner Hub = Many props have a sacrificial centre. If you were to hit something you would therefore break this rather than damaging your engine. ▸ Ribs / Splines = Joining points between the inner & outer hubs. On through exhaust props, some of the exhaust travels through this gap between the inner & outer hub.
- 4. WWW.MARINE-EDUCATION.CO.UK PROPELLER ANATOMY ▸ Diffuser Rim = The flared section on the back end of some propellors. ▸ This flare helps stop exhaust from travelling back onto the blades which would reduce thrust.
- 5. WWW.MARINE-EDUCATION.CO.UK DIAMETER ▸ Diameter is the circle swept by the tips of the propeller blades ▸ Increased diameter means increased thrust, but also increased drag
- 6. WWW.MARINE-EDUCATION.CO.UK PITCH ▸ Pitch is the theoretical movement forward of a prop during one revolution if it was going through a hard surface like a drill goes through wood.. ▸ However, as it is travelling through water there will be slip therefore the distance is less.. ▸ The amount of slip varies from boat to boat.
- 7. WWW.MARINE-EDUCATION.CO.UK CUPPING ▸ Cupping is the curved lip on the blade. ▸ This allows the prop to have a better ‘bite’ on the water. ▸ Cupping reduces slip, ventilation and allows for a better hole shot. Hole Shot = From dead stop (in the hole) to being up on the plane.
- 8. WWW.MARINE-EDUCATION.CO.UK RAKE ▸ Rake is the angle that the blades slant in relation to the outer hub. ▸ Rake effects the flow of water through the prop and boat performance. ▸ Assuming rake is aft (as most outboard props) this reduces the wetted area (friction) and ensures a higher top end speed. ▸ Props with less rake are generally fitted to displacement craft.
- 9. FOR MORE TUTORIALS VISIT ‘FREE TUTORIALS’ ON MARINE-EDUCATION.CO.UK Marine Education RYA Training Centre WWW.MARINE-EDUCATION.CO.UK