Boating and Sailing.pdf - Moja ladja

Diameter
Blade
Hub
Prop nut
Prop shaft
Chapter 3: Picking a Proper Prop
An “over-the-hub” prop, shown in the following figure, is less common except on performance
boats. The hub is much smaller and is solid steel in this design. They create less
drag and consequently can run faster. The motor makes more noise, but if you’re after
maximum speed you don’t care, do you?
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The typical three-blade propeller
includes a tubular
barrel or hub through which
the engine exhaust passes.
Over-the-hub props are
designed for high-speed boats.
They feature a smaller, solid
barrel compared to throughthe-hub
models.
Most props have a rubber or composite core pressed into the center of the hub that acts
as a shock absorber should the prop strike bottom. It gives a bit and springs back into
shape on light strikes, but tears in a hard strike—you have to get a new hub core pressed
in, but you don’t destroy the very expensive gears and shafts in the lower unit. The
stripped hub will usually get you home at idle speed but won’t move the boat at higher
rpms.