Hydraulic steering systems

Selection of a hydraulic steering system

Selection of a hydraulic steering system

• For boats fitted with outboard motors

To select a steering system in our range, first determine the maximum horse power developed by the outboard motor(s) and the rotational direction of the propellers on installations with several motors.

Indeed :
For twin motor installations working in the same rotational direction, add the power of both motors (see example below)
Whereas :
For twin motor installations working in counter-rotation, take into account the power of one motor only + 20% (see example below)
Examples :
  Maximum Power
For the installation of one single motor 1 x 115 H.P. = 115 H.P.
For twin motor installation 2 x 115 H.P. (same rotational direction) = 230 H.P.
For twin motor installation 2 x 115 H.P. (in counter rotation) : 115 + 20% = 138 H.P.
Now select in our range the hydraulic steering which complies with the maximum power of the motor(s).
Examples :
Maximum power 115 H.P.
Maximum power 230 H.P.
Maximum power 138 H.P.
For twin motor installations when the calculated maximum power exceeds the maximum power the steering system is given for (ex.: 2 x 200 H.P. in same rotational direction = 400 H.P.), it will be necessary to install a cylinder on each motor with a parallel hydraulic circuit (see “Different types of assemblies”).
Note : for 4 blade propellers or more, please contact us.

• For boats fitted with a rudder with speed not exceeding 25 knots, the torque of the rudder or rudders is calculated according to following formula and corrections.
It must be known that the torque necessary to manoeuvre a boat depends on :
- the speed of the water flowing on the surface of the rudder at a certain angle,
- the rudder size,
- the total sweep of the rudder (and part of the boat), if the rudder shaft is not perpendicular,
- the compensating surface of the rudder.

Torque Calculation Formula for Speed below 25 Knots
C = S x [ (0,4 Lg) – Lc ] x V² x K

Start the calculation

C = Torque in kpm
S = Total surface of rudder (H x Lg) in sq. m
H = Height of rudder in m
Lg = Width of rudder in m
Lc = Compensation width in m
V = Maximum speed of the boat in knots
K = Coefficient according to total angle of rudder

Port to starboard
K = 15,89
Port to starboard
K = 17,80
Port to starboard
K = 19,52


Corrections in function of the type of boat :
• For sailing-boats
C x 0,5
• For a boat with a steering nozzle
C x 2,0
• For twin engine power boats with 1 rudder
C x 0,5
• For boats fitted with several rudders (catamarans, trimarans, monohulls), multiply the calculated torque result by the number of rudders fitted on the boat.

Once the torque is known, the appropriate cylinder is selected and one or two manual pumps will be added accordingly.

Warning : If you select a pump with a higher flow rate in order to reduce the number of wheel turns, you will have to fit a wheel au diamètre conseillé.

• For pleasure boats with planing or semi-planing hulls and speed exceeding 25 knots, the cylinder may be selected by using the chart below.

Length of Hull

Cylinder Type – 1 Rudder

Cylinder Type – 2 Rudders

8 metres

VHM 40 DTP – code 2200075

VHM 32 DTP – code 2200059

10 metres

VHM 40-254 – code 2200496

VHM 40 DTP – code 2200075

12 metres

VHM 40-254 – code 2200496

VHM 40 DTP – code 2200075

14 metres

VHM 50 DTP – code 2200497

VHM 40-254 – code 2200496

This chart is given as an indication only

Description | Working principle | Assembling diagrams | Selection of a system