Page 355 - Lewmar

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Wide Angle Geometry
The lever geometry for Lewmar transmission systems is based on the principle of Wide Angle Geometry. This results in a very
direct steering at midships and a more indirect and powerful steering at full rudder.
Due to this unique feature, the total number of turns of the wheel on a transmission steering system can be reduced by
30-40% compared to a cable system with the same maximum rim loads. This effect is achieved by an unequal length of the
output and tiller lever. The output lever has 134mm centres and the tiller lever 203mm. The diagram to the below left shows
the mechanical advantage (lever reduction) in relation to the rudder angle. Around amidships the reduction is quite constant,
and above 15 degrees rudder the mechanical advantage nearly doubles compared to the amidships advantage.

The consequence of wide angle geometry is the offset angle of the levers in amidships position. This offset angle is necessary
to achieve the same travel to port and starboard. The offset angle varies with the distance from the output lever to the tiller
lever. Offset angles can be avoided when the complete gearbox is put on an offset distance.

Tiller Lever Pedestal Output Lever

° ° °
°
Different gear ratios can be used to suit all applications:

MECHANICAL ADVTANAGE AT
TYPE GEAR RATIO MIDSHIPS TURNS HO/HO MAX RUDDER TORQUE TYPICAL BOAT SIZE
 .  
™  : : . .
™   : : . .
™  : : . .
™  . : . : . .

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