For boats equipped with a hydraulic steering, it will be necessary to determine:
– The volume of the steering cylinder (take the biggest volume in case of a single rod cylinder)
– Available voltage on board (12 VDC, 24 VDC, etc.)
For planing or semiplaning hulls, the power pack will be selected in function of its flow rate so that the steering cylinder will run its complete stroke within 10 to 12 seconds.  
For displacement hulls, the power pack flow rate must enable the steering cylinder to run its complete stroke within 15 to 17 seconds.  
Examples  
Speed boat, planing hull with a 239 cc cylinder – Available voltage 12 VDC  
60 seconds (1 minute)  12 seconds (required time) 
x 0.239 litre (239 cc) = 1.195 litre / minute 
The flow rate of the required power pack will be 1.19 litre / minute, therefore we will select a reversible power pack with adjustable flow rate type RV2 (12 V)  
Fishing or work boat, displacement hull with a 2,307 cc cylinder – Available voltage 24 VDC  
60 seconds (1 minute)  15 seconds (required time) 
x 2.307 litre (2307 cc) = 9.228 litre / minute 
The flow rate of the required power pack will be around 9 litres / minute, therefore we will select a power pack type HF 1.5 – 9 (24 V)  
For boats equipped with a mechanical steering (wire ropes, cables, rack and pinion), it will be necessary to determine:
– The rudder(s) torque
– The available voltage on board (12 VDC, 24 VDC, etc.)
Torque Calculation: For boats fitted with a rudder with speed not exceeding 25 knots, the torque (C) of the rudder or rudders will be calculated according to the formula and correction coefficients below: C = S x [ (0.4 Lg) – Lc ] x V² x K
