Volvo D11 series, Installation Manual

Page: 35 / 212

General arrangement and planning
33
Propeller selection
The combination of ratio, shaft diameter and propel-
ler size can be calculated by using
the Volvo Penta
computer program. Calculation of the correct pro-
peller size can be done by the Volvo Penta organisa-
tion if so desired. In this case all details of the boat
(preferably drawings) must be provided in good time.
A = Engine full load curve
B = Propeller load curve (propeller OK)
C = Recommended max operating range
The propeller should be chosen with the greatest of
care. Consider the
space between the hull and skeg.
Refer to propeller recommendations and propeller
shaft angles, and the recommendation for free space
between the propeller and hull. See information on
the following page.
On planing boats the bottom over the propeller is
often rather flat. The hull can be reinforced on the
inside to reduce noise and vibrations caused by the
propeller blade pulses.
A
B
C
rpm
kW
For the best propeller efficiency, the angle of the pro-
peller shaft in relation to the water line should be as
small as possible. The larger the shaft angle the low-
er the efficiency. Shaft angles exceeding 2° should
be avoided if possible. This means that with the boat
lying still, the propeller angle should not exceed 2°.
This applies especially to planing boats. Larger shaft
angles may affect the speed, sound and vibrations
negatively.
Check the shaft angle. If the shaft angle exceeds 2°,
the use of a smaller propeller should be considered.
This can be compensated by more blades.
The keel or the propeller shaft brackets in front of the
propeller should have a profile creating a minimum
of drag and turbulence. Also the shape of a tunnel is
very important. A poor tunnel design can create a lot
of turbulence in the propeller and reduce the boat’s
buoyancy at the stern.