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From: (no name) (no email)
Date: Thu Jul 27 2006 - 10:02:58 EDT
I confess to being a mechanical control luddite, but I have considerable
experience with electronic controls in aerospace applications. Some degree of
delay is inherent in most electrical engine and steering controls. The majority of
these controls operate by using a small motor driven actuator to actually
move a mechanical linkage to the gearbox, injection pump, or steering gear. The
motors used are relatively low powered, usually less than .1 hp, almost always
drawing less than 10 amps. To compensate for the low power, the actuator screw
or rack has a relatively fine pitch and the lock to lock time may be as much
as five seconds. It is possible to get quicker reaction time with vacuum or
hydraulic actuators but these impose another layer of complexity and cost.
In contrast, humans, especially in panic situations, can exert up to a full
horsepower for a few seconds, jamming the control from one extreme to the other
in a small faction of the time it takes an electric control to respond. If I
spin the wheel, I can drive my rudder from lock to lock in two seconds. It
takes my autopilot at least 10 seconds to do the same. Similarly there is almost
no delay from forward to reverse in my mechanical shift gear. It takes a
friend's electrically shifted gear at least five seconds to accomplish the same
task.
Close quarter boat maneuvering is qualitatively different with electronic
controls. You must plan your actions further in advance, anticipating a delay of
several seconds before the boat begins to respond. In close in maneuvering
electrical controls make a 30 foot trawler respond like a 60 foot trawler. No
quick slamming into reverse to stop headway when pulling into a slip.
You may well wonder how I know this.
Larry Z
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