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.
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
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