AG Publications Aquafax Equipment Catalogue

HYDRAULIC STEERING SYSTEMS

www.aquafax.co.uk

MAIN HEADING TECHNICAL INFORMATION

HOW TO CALCULATE THE RUDDER TORQUE

GENERAL SELECTION GUIDE

When the torque necessary to manoeuvre a boat is not specified by naval architect nor by the shipbuilders yard, it can be calculated as follows:- 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 rudder (& a part of the boat) when rudder shaft is not perpendicular. • The compensating surface.

A hydraulic manual steering system consists of three basic main components: a) The helm pump b) The cylinder c) The hose or tubing required to connect the cylinder to the helm pump. To select the type of cylinder and the size of the helm pump best suited to your boat, take into consideration the following variables: 1) Type of boats (planing or displacement). 2) Type of engine (outboard, inboard, stern drive). 3) Number of engines. 4) Total power of the engines. 5) Space available in the splash well & dash areas for the steering components. When making your choice, specify the following options: 1) Number of steering stations. 2) Additional features such as autopilots.

Torque calculation for a maximum speed about 25 knots: T = S x [(0.4a) -b ] x V2 x k

T = Torque in kgm S = Total surface space of the rudder in m2 (h x a) h = Height of the rudder in m a = Width of rudder in m b = The value of the compensation in m V = Speed of the boat in knots k = Coefficient according to the total angle of rudder - Port to starboard 50° k = 10.84 - Port to starboard 60° k = 13.01 - Port to starboard 70° k = 15.89 - Port to starboard 80° k = 17.80 - Port to starboard 90° k = 19.52 Straightening according type of boats: - For boats equipped with jet engine T x 1.3 - For power boats with two engines & one rudderT x 0.5 - For sail boats T x 0.5 - For twin rudders T x 2

H

111

Number of Turns in Relation to Steering Effort

B

A

When choosing the responsiveness of a steering system, remember that the steering wheel effort is proportional to the number of wheel turns: the quicker the steering, the harder the effort. The number of wheel turns lock to lock depends on the volume of the cylinder and the displacement of the helm pump. Other factors that can influence steering effort are the vessel speed, rudder size, engine power, propeller selection, oil viscosity, sea conditions and hull type (displacement, planing etc).

EXAMPLE

The maximum torque on the rudder blade is given by: T = S x [(0.4a)-b] x V2 x k T = S x (0.4a-b) x V2 x 15.89 T = ( 0.5 x 0.35 ) x [(0.4 x 0.35 ) - 0.10 ] x 22 2 x 15.89 T = 0.175 X 0.04 x 484 x 15.89 T = 53.9kgm

Assume a rudder with: Height of 0.5m (h) Overall width of 0.35m (a) Balance of 0.10m (b) Maximum boat speed = 22 knots Port to Starboard = 70º

Assuming twin rudders Maximum steering torque = (53.9 x 2) = 107.8kgm Therefore the appropriate cylinder = 4-48034 (max torque rating of 111kgm)

CROSS REFERENCE HELM PUMPS - General reference only

CROSS REFERENCE CYLINDERS - General reference only

PART NO.

MOUNTING

ULTRAFLEX

TELEFLEX ®

PART NO. 4-48161/2/3 4-48066/7/8 Silversteer ™

TYPE

ULTRAFLEX UC95-OBF UC128-OBF UC128-SVS UC68-OBS UC132-OBS

TELEFLEX ®

14-48120-1 4-48003 4-48000 4-48000NV

Front Front Front Front

UP18

Baystar ™ HH4311 Baystar ™ HH4314 Seastar ™ 1.7 HH5269 Seastar ™ 1.7 HH6544 Seastar ™ 1.7 HH5271 Seastar ™ 1.7 HH6541 Seastar ™ 1.7 HH5261 Seastar ™ 2.0 HH5273 Seastar ™ 2.0 HH5760 Seastar ™ 2.0 HH6543 Seastar ™ 2.4 HH5272 Seastar ™ 2.4 HH6542 Seastar ™ 2.4 HH5262 Seastar ™ 3.0 HH5283 – –

Outboard Outboard Outboard Outboard Outboard

Baystar ™ HC4645 Seastar ™ HC5345 Seastar ™ HC6345

UP20 F UP25 F

4-48060 4-48064 4-48030 4-48031 4-48032 4-48034 4-48035 4-48055

–

UP25NV F

Seastar ™ HC5370/5328 Baystar ™ HC4461-3

4-48001 4-48006 4-48007 4-48008 4-48010 4-48011 4-48012 4-48015 4-48016 4-48017 4-48018 4-48019 4-48020

Tilt

UP25 T UP28 F UP28 T UP28 R UP33 F UP33 T UP33 R UP39 F UP39 T UP39 R UP45 F UP45 T UP45 R

Inboard Inboard Inboard Inboard Inboard Inboard

UC69-I UC116-I UC168-I UC215-I UC293-I UC378-I

Front

Seastar ™ HC5312 Seastar ™ HC5314 Seastar ™ HC5319

Tilt

Rear Front Front Rear Front Rear Front Tilt Tilt

– –

4-48010NV

UP33NV F

Tilt

–

Rear

Seastar ™ 3.0 HH5265