Seiwa SW AP01 - Manual (Page 9)

degree off course. In large or slow vessels it would be more and in light, fast boats it may be
less.
Setting the rudder factor too high causes oversteering or ‘snaking’ as illustrated in Fig 1.2.
Too low a setting causes understeer and a sluggish response. Fortunately, most vessels
tolerate a range of settings and still steer well.
UNDERSTEER
REFERENCE
COURSE
OVERSTEER
Figure 1.2. Illustration of oversteer if the rudder factor is set too high and understeer if it is
set too low.
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Control Mode - Normal or Rough
The CONTROL MODE setting is influenced by the sea conditions and the weight of the
vessel. The NORMAL applies helm in proportion to the course error and the rate of turn.
The ROUGH mode is used when the vessel rolls and yaws in a heavy sea. Rudder activity
is quietened down by not reacting to small heading shifts, but full control is applied as the
shift becomes larger. The rate of turn component in the helm correction is adjustable and is
important for vessels whose helm response is slow and/or continue to turn for some time
after helm is removed. When there is a turn-rate (or counter rudder) component, normal
helm is applied to start the vessel turning. As the turn rate builds up, the helm is backed off.
When the vessel is close to the reference course, reverse helm or counter-rudder is applied
to stop the turn.
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