How to determine the correct VETUS steering
The number of wheel turns from lock to lock
When a reduced number of wheel turns from starboard to port is required, a steering pump with larger capacity should be selected. It should be taken into account that the force to be applied to the steering wheel becomes relatively greater, possibly leading to the necessity of selecting a larger diameter steering wheel. Take a look at the large selection at this Webside!
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VETUS hydraulic steering systems consist of a hydraulic pump and cylinder, connected by means of tubes (copper, steel or nylon).
The pump is of the axial piston type, with small pistons inside, which are directly actuated by the steering wheel; the only good system for safe and reliable handhydraulic steering. The cylinder is of the double-acting type and mounted on a base, allowing it to swing according to the arc described by the rudder tiller. Vetus-Online.com has just what you need + large expertise and quick delivery!
The choice of the correct cylinder is determined by the rudder torque in Nm (or kgm). The rudder torque is the determining factor (Torque = force x lever). To ascertain the correct rudder torque, only the maximum speed of the vessel, the surface area of the rudder blade and the maximum rudder angle (in degrees) are of importance. Information such as length of boat and engine power are irrelevant. With a few admitted exceptions, the rudder performs best with a maximum rudder angle of 35° to either side. Contrary to what is sometimes claimed for rudders with normal dimensions, a larger rudder angle does not enhance the manoeuvring capabilities of a vessel.
The formula to determine the rudder torque reads:
M (torque) = F x b (per rudder)
In other words: the force F, which is applied to the rudder (given in Newton = N), is being multiplied by the lever "b ", being the distance between the centerline of the rudder stock and the centre of pressure which lies on the line X-Y.
F (the force applied to the central line XY) - taking into consideration a maximum rudder angle of 2 x 35° - is constituted in the following manner: F = 23.3 x A x v2 in Newton (N), or: F = 2.33 x A x v2 in kgf.
A = total surface area of rudder blade in m2. v = speed in km/hour. A rudder without balance section requires the formula: b = 0.37 x c (in metres); A rudder with balance section calls for the formula: b = (0.37 x c) - e (in metres).
Calculation example of one rudder with balance section
The maximum speed of the boat is 16 km/hour (v); the total width of the rudder blade is 57 cm (c); the width of the balance section is 9 cm (e); the height of the rudder blade is 100 cm (h). F = 23.3 x 0.57 x 1.00 x 162 = 3400 N (340 kgf) b = (0.37 x 0.57) - 0.09 = 0.12 m.
Therefore, the rudder torque amounts to 3400 x 0.12 = 408 Nm (41 kgm). So, the VETUS hydraulic steering to be selected in this case is model MTC52. W ith a twin rudder installation, the required torque is 2 x 408 Nm = 816 Nm, which makes model MTC125 the one to choose. We recommend that you consult VETUS for an accurate calculation. We also calculate the effects of the propeller wash, as well as the torque when going astern. Because smaller vessels tend to respond quite sharply to the rudder commands, the maximum rudder torque is not used and a reduction of 10 to 20% off the calculated maximum torque is quite acceptable most of the time. Careful: some manufacturers of hydraulic steerings have already taken such reduction into account when stating their capacity (torque). We, at VETUS, are of the opinion however, that the choice of whether or not such reduction should be applied, is exclusively the option of the naval architect.