BS 7493:1991 download free.Specification for Remote steering systems for single outboard motors of 15 kW to 40 kW power for small craft.
I Scope
BS 7493 specifies requirements and test methods for remote push-pull cable steering systems and their major component items, used for small craft with a single outboard motor of 15 kW to 40 kW power.
2 DefinitIons
For the purposes of BS 7493, the following definitions apply.
2.1 steering system: Assembly including all components necessary to transmit remote manual effort to the outboard motor.
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 motormounted steering system by which he linear force of the output ram Is transmitted to the motor steering arm.
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 shafl centre to the hole centre in the steering output ram at the mid- travel position.
The steering cable shall also be marked by the manufacturer that the maximum power permlssble Is 40 kW.
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.
The helm assembly shall be permanently marked as above with the Indication that the maximum permissible power Is 40 kW.
5.6 Plastics and elastomers which may be exposed to sunlight shall be chosen to resist degradation by ultraviolet radiation.
5.7 PlastIcs and elastomers which may be Installed in engine compartments shall be chosen to resist degradation by saline atmospheres, fuel, oil and heat.
6 InstallatIon
6.1 Except for installations specifically intended for boats or outboard motors with special requirements, either the motor-mounted or the boat-mounted stoering system shall be used.
6.2 II installIng motor-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 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 centreline as specified In figure 2.
6.4 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.
6.5 Steering-wheels and helm shafts shall be se• lected to lit each other. Current lit configurations are shown In figure 7.
6.6 Steering systems and components as installed
shall be capable of meetIng the test requirements in
7.1.
6.7 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 Test requirements
7.1 As-installed tests
These tests are intended to establish the acceptability of the design strength of steering systems as installed In a boat to the Interface with the outboard motor.
7,1.1 Steering systems shall withstand a static load in either direction of 2 200 N applied at the connection hole or the steering output ram along the axis of the steering output ram without deformation that, following the test, will cause any loss in steering capability or any dimensional change that resuits In non-compliance with figure 2. The permanent deformation shall not exceed 6,35 mm measured along the axis of the output ram.
7.1.2 Steering systems shall withstand a single tangential load in either direction of 450 N applied as appropriate:
-— at any point on the steering-wheel rim,
— at the centre-point of any handgrip of an external spoke steering-wheel, or
— at the point of maximum leverage on other steering devices,
and a subsequent separate single axial load or 670 N, In each direction, distributed over not more than 100 mm of the rim, spoke or handgrip, at any location maintaining minimum retained system perforrnance. Upon application of the indicated loads there shall be no fracture of the mounting surface or boat structure, nor deformation such that the required loads cannot be achieved.
7.2.2 Helm assembly tests
Helm assemblies shall incur no loss of operating function after the following tests, when equipped with the largest diameter and deepest dish steering-wheel for which the helm Is rated.
Helms for two-cable systems shall comply with each cable installed Individually.
7.2.2.1 Axial load test
A 670 N push-pull load distributed over not more than 100mm of the
— steering-wheel rim,
— handgrip of an external spoke steering-wheel, or
— handgrip at the point of maximum leverage on other steering devices,
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.
7.2.2.2 Tangential load test
A 450 N load In each direction shall be applied
— at any point on the steering-wheel rim.
— at the centre-point of any handgrip of an external spoke steering-wheel, or
— at the point of maximum leverage on any other steering devices,
at any single location, tangential to the plane or the steering-wheel rim or In the plane of motion of other steering devices, at any point in Its total steering range, for 10 cycles for a duration of 5 s per loading.
7.2.3 SteerIng-wheel tests
NOTE 3 The thermal conditioning (72.3.1) and ultraviolet exposure (7.2.3.2) may be omitted on wheels of all metal and/or wood construction and wheels Whose plastics parts are not structural.
7.2.3.1 Steering-wheels shall be subjected to three cycles of thermal conditioning before mechanical tests are performed. One cycle of thermal conditioning Is defined as
3h.at2l°C±2°C,
— 3hat—34°C±2°C,
— 3 h at 21 °C ± 2 °C.