• fr
  • en
Hydraulic Steering Systems
For boats fitted with a rudder with speed not exceeding 25 knots, the torque of the rudder(s) is calculated according to the following formula and correction coefficients.

It should be pointed out that the necessary torque to maneuver a boat depends on:

  • the speed of the water flowing on the surface of the rudder at a certain angle,
  • the rudder dimensions,
  • the total sweep of the rudder (and part of the boat), if the rudder stock is not perpendicular,
  • the compensating surface of the rudder (balanced rudder).

Torque Calculation Formula for Speed below 25 Knots:

C = S x [ (0.4 Lg) – Lc ] x V² x K


C = Torque in kgm safran_scheme
S = Total rudder surface (H x Lg) in sq.m
H = Rudder height in m
Lg = Rudder width in m
Lc = Compensation width in m
V = Maximum speed of the boat in knots
K = Coefficient according to the total rudder angle
Port to Starboard 70° K = 15.89
Port to Starboard 80° K = 17.80
Port to Starboard 90° K = 19.52
  Corrections in function of the type of boat:
For sailing boats C x 0.5
For a boat with a steering noozle 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 by the number of rudders fitted on the boats.

Once the torque has been calculated, the appropriate cylinder(s) will be selected and the remaining components of the steering system can be defined.

Please contact us for boats fitted with a rudder, when the speed exceeds 25 knots.