Volvo D11 series, Installation Manual

Page: 37 / 212

General arrangement and planning
35
Ratio, Main type of Speed
approx. operation range
Work boats,
6:–3: Displacem. boats, 4–2 kn.
High pulling power,
Towing, Trawling
Work boats,
3:–2.5: Displacement boats, 8–7 kn.
Low speed planing boats,
mainly free run
Semi-planing to planing
2.5:–2: boats, Patrol boats, 6–26 kn.
Sport fishing
and Pleasure boats
Planing boats,
2:–.5: Patrol boats, 25–35 kn.
Sport fishing,
and Pleasure boats
High speed planing
.5:–: boats, high 35–45 kn.
performance,
Pleasure boats and
similar
Ratio, Main type of Speed
approx. operation range
Work boats,
4:–3: Displacem. boats, 4–8 kn.
High pulling power,
Towing, Trawling
Work boats,
3:–2.0: Displacement boats, 6–0 kn.
Low speed planing boats,
mainly free run
Semi-planing to planing
2.5:–.5: boats, Patrol boats, 0–5 kn.
Sport fishing
and Pleasure boats
Propeller rotation
For a single installation, a right or left-hand rotating
propeller can be chosen. The rotation direction is
sometimes dependent of the type of reverse gear be-
ing used.
For twin installation, the starboard propeller should
always rotate clockwise and the port propeller anti-
clockwise seen from the aft forward. Otherwise there
is a risk that air bubbles will be drawn down into the
water between the two propellers which can cause
ventilation.
Choice of reduction ratio
The propeller shaft usually has lower speed than the
engine. This is normally achieved with the reduction
in the reverse gear.
As a rule the largest possible ratio should be chosen
for slow-going displacement boats. It then follows
that the propeller diameter can also be relatively
large with high thrust within the applicable speed
range. Depending on the hull type and speed range,
a smaller ratio can be chosen for higher speed, if
required. See the table. This is to obtain highest
thrust within the respective speed range. If the ratio
is chosen outside of the recommendations the thrust
can be lower than the optimum calculated power. The
boat’s top speed is not necessarily affected.
A check must always be done that the hull has suffi-
cient space for the propeller according to information
in chapter
Propeller selection
.
In order to select the optimal gear ratio a calculation
have to be made. The following tables could serve as
guidelines.
D9/D12/D16 engine revolution range 1800–2800
rpm with conversional shaft/propeller system
D5/D7 engine revolution range 1900–2300 rpm
with conversional shaft/propeller system