Wednesday, January 26, 2011

Teaching a car driver how to steer a ship



Controlling the rate of turn while steering a ship is somewhat analogous to controlling the speed of a car.

If  we name certain settings of the car throttle as follows: idle, slow, moderate  in the analogy they match up to rudder angles, amidships and say 5 and 10 degrees of rudder.  Using the car's brakes is similar to using counter rudder, that is rudder in the direction opposite the turn.

Note that cars speed is analogous to the ship's rate of turn, not it's speed.




In story form the analogy works like this:   Imagine the car sitting at a stop sign on a road  and a ship on a steady course about to make a course change.

In the car we push the throttle to a moderate setting until the car reaches 35 miles an hour at which point the throttle is reduced to a low setting to maintain the 35 miles an hour. As the next stop sign is approached we lift off the throttle and allow the car to coast for a while and as the stop  draw closer we apply the brake as required to stop smoothly.

On the ship we arrive at the turn, we put on 10 degrees of rudder until the ship starts turning at the desired rate at which point we reduce to 5 degrees of rudder. As the ship's heading approaches the new course we put the rudder amidships and allow the rate of turn to decrease slightly. As we approach closer to the heading of the new course we apply opposite rudder as required to stop the swing at the new heading.When the ship is steady on the new course we again put the rudder admidships.

I have explained steering to a couple of ABs this way with good results and yes I know, ABs are supposed to know how to steer.

K.C.

1 comment:

Sally said...

It's OK, you can drive!