BS 7492:1991 download.Specification for Remote steering systems for small craft.
1 Scope
BS 7492 specifies requirements and test methods for remote push-pull cable steering systems and their major component items, used for small craft with single and twin Installations of outboard motors of over 15 kW power, and all inboard motors, Inboard motor-outdrives, and waterjet drives.
2 DefinitIons
For the purposes of BS 7492, the following definitions apply.
2.1 steerIng system: Assembly Including all components necessary to transmit remote manual effort to the rudder, outboard motor, inboard-outdrive or water-jet drive.
2.2 boat-mounted steering system: System in which an output ram guide tube Is secured to the boat.
2.3 motor-mounted steering system: System in which an output ram guide tube Is secured to the engine.
2.4 drag link: Device in a motor-mounted steering system by which the linear force of the output ram Is transmitted to the motor steering arm.
2.5 helm: Mechanism, exclusive or a steering- wheel or other means for manual application of controlling force, by which controlling force is fed into a steering system cable or other force- transmission means.
2.6 minimum retained system performance: System capability after test(s) such that at least 90 % of the steering arc normally available each side of the mid-position may be obtained by exertion of no more than 27 Nm of torque at the helm, through the wheel or other normal control.
This criterion does not define steering system performance while a boat is underway but is intended to provide quantitative limits for design and test urpose s.
3 General requirements
3.1 When steering systems are factory-installed In the boat, the complete system shall be supplied. In outboard motor-boats, the system shall be supplied complete to the interface point at the ram output end as shown In figure 1.
4.7 inboard-outdrlves shall be designed with proper geometry to ensure that a torque of 680 Nm applied about the outdrive steering axis will not resuit in a steering component loading greater than that specifled in 7.2.1.
5 Steering system requirements
5.1 Motor-mounted steering systems shall meet
the dimensional requirements Indicated In figure 1,
figure 3 and figure 4.
5.2 Boat-mounted steering systems for outboard motor installations shall meet the dimensional requirements Indicated in figure 1 and figure 2. When a joint as shown in figure 2 is replaced by a universal joint with two movement axes, the axis perpendicular to the transom face shall be located 0 to 13 mm above the motor clamp bracket horizontal mounting face. The second axis shall be 100 mm to 115 mm from the inner surface of the transom and shall be not more than 28,5 mm from the first axis toward the motor.
5.3 Steering cables shall be marked at the engine end with a steering system length which shall be the length from the steering-wheel shaft centre to the hole centre In the steering output ram at the mid- travel position.
5.4 Installation Instructions for steering helms shall include recommendations for the maximum diameter and deepest wheel dish (see figure 5) that may be used with the helm. In addition, the maximum diameter and deepest wheel dish Information shall be permanently marked on the helm assembly to be visible when the helm Is Installed with the wheel removed.
6.2 If installing motor-mounted steering systems in outboard motor-boats, steering cables or other rorce-transmisslon means shall be selected so that, as installed and at mid-travel position, the output ram or equivalent component connection point shall reach at least 270 mm beyond the motor centreline as indicated in figure 6.
6.3 If installing boat-mounted steering systems in outboard motor-boats, steering cables or other force-transmission means shall be selected so that, as installed and at mid-travel position, the output ram or equivalent component connection point will reach at least to the motor centreline. The cable shall be attached to the boat to position the cable- anchor swivel with respect to the transom-motor centreitne as specified in figure 2.
6.4 lnboard-outdrlve or water-jet drive installations shall be such that with any combination of drive turn and tilt, there shall be no damaging Interference between the Inboard-outdrive or jet drive, its accessories and any part of the boat or steering system.
6.5 Cables shall be Installed with as few bends as practicable. Bends should have as large a radius as practicable and the radius shall not be smaller than the manufacturer’s recommended minimum.
6.6 Steering-wheels and helm shafts shall be selected to fit each other. Current fit configurations are shown in figure 7.
6.7 Steering systems and components as installed
shall be capable of meeting the test requirements In
7.1.
6.8 if the steering cable passes through the side of an outboard motor well below the static float plane, the cable access port shall be appropriately sealed.
7.2.3.3 At the completion of the thermal conditioning and ultraviolet exposure, the wheel shall be maintained at a temperature of 20 °C to 24 °C for at least 3 h. It shall then, in sequence, withstand the mechanical tests In 7.2.3.3.1 to 7.2.3.3.3.
7.2.3.3.1 Axial load test
A 670 N push-pull load, distributed over not more than 100 mm of the
— steering-wheel rim, or
— handgrip of an external spoke steering-wheel,
shall be applied, at any single location, in a direction parallel to the steering shaft axis for 10 cycles for a duration of 5 s per loading without fracture or permanent deformation in excess of 25,4 mm at the rim. or spoke handgrip.
7.2.3.3.2 Tangential load test
A 450 N load in each direction shall be applied
— at any point on the steering-wheel rim, or
— at the centre-point of any handgrip of an external spoke steering-wheel,
at any single location, tangentially In the plane of the steering-wheel rim or in the plane of motion of other steering devices, for 10 cycles for a duration of 5 s per loading without fracture.
7.2.3.3.3 Impact load tests
The fixture shown in figure 9 and the following procedure shall be used.
The Impact test apparatus to be used (see figure 9) shall be a completely filled 250 mm diameter leather bag, containing lead, producing a force of 785 N in total and suspended on a free swinging cable, such that the centre of mass is 2250 mm to 2300 mm from a supporting pivot. The impact face of the bag shall be a 250 mm diameter end. The bag shall be elevated through sufficient arc to create the desired Impact value upon a rigidly mounted steering-wheel by swinging the bag as indicated in figure 9. The fixture shall be rigidly secured against movement. Devices other than that specified such as a falling weight bag may be used providing equivalence can be verified.