Volvo Penta KAMD300, Руководство по установке, Страница: 28 / 140

General arrangement and planning
26
Propeller selection
The combination of ratio, shaft diameter and propeller
size can be calculated by using
the Volvo Penta
computer program. Calculation of the correct propel-
ler size can be done by the Volvo Penta organisation
if so desired. In this case all details of the boat (pref-
erably 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.
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 lower
the efficiency. Shaft angles exceeding 12° should be
avoided if possible. This means that with the boat ly-
ing still, the propeller angle should not exceed 12°.
This applies especially to planing boats. Larger shaft
angles may affect the speed, sound and vibrations
negatively.
Propeller theory
To get the best performance out of your boat, you
need to select the propeller and gearing that will suit
your particular boat, engine and speed range.
Below you will find a brief description of how propeller
systems are designed. It is not just the engine capaci-
ty determines the speed of the boat; it depends just
as much on the efficiency of the reverse gear and the
propeller system. Using the right propeller system will
not only give you good fuel economy and higher
speed but you will also experience greater comfort,
with less noise and vibration.
The following description is very general and de-
scribes only superficially how propellers are designed.
The propeller manual
Propellers publ. no. 7739174
gives more detailed information.
Propeller and performance computer
program
Over the last year, Volvo Penta has been developing
computer programs for calculating speed, gear ratios
and propellers. This is excellent for predicting speed
and propellers simply and safely.
The estimated speed in the individual computer pro-
grams is based on the experience gained from a num-
ber of installations.
Propeller calculations
Theoretical speed and propeller calculations are made
using well-established methods and a number of prac-
tical test results, but are still a result of approxima-
tions and estimations. We believe that for a standard
type of boat they can give you a reasonable good esti-
mation, provided that correct and complete input is
available. However the Volvo Penta organisation can
not take any responsibility for the final result which
only can be found out during a sea trial.
A
B
C
rpm
kW