Simrad Hydraulic Linear Drive
24
20220109E
6
APPENDIX
6.1
Calculation of the force against the rudder
1. When the rudder torque is known.
The rudder torque is usually obtained from the boat builder.
To find the force against the rudder, the length of the rudder tiller
must first be known. This can be calculated from the formula:
R =
l
a
sin
(m)
where R = rudder tiller length
a = one half of the rudder angle
l = one half of the stroke length(0.10m/0.17m)
The force F against the rudder is calculated from the formula:
F
r
=
M
R
(kp)
where
F
r
= rudder force
M = rudder torque (kpm)
R = rudder tiller (m)
Use the table on page 10 to find the appropriate drive unit. If the boat
is going on cruises for several days, it is recommended to select a unit
where Fr not exceeds 70% of listed max. thrust.
2. When the rudder torque is unknown.
First the helm torque must be found. The following
measurements/calculations must be carried out:
At full speed ahead and the rudder hard over, find the maximum force
F required to turn the helm by using a spring balance.
Measure the radius r of the helm. The helm torque is calculated from
the formula:
M
r
= F x r (kpm)
M
r
= helm torque
F = helm force (kp)
r = helm radius (m)
To convert the helm torque to rudder torque
the turn-over ratio must first be found:
F
r
