Tuesday, December 4, 2007


The seaman's eye remains the best aid to shiphandling and maneuvering in channels and restricted waters. Radar and other electronic aids are useful for navigation in restricted visibility, but the gyro and fath­ometer remain the shiphandler's primary tools.
The gyro is used, to maintain direction, supplying the point of reference for almost all maneuvers. The gyrocompass also serves as an accurate audible rate of turn indicator as it clicks off the fractions of each degree during a turn. It is surprising how accurately an experi­enced seaman can judge the rate of turn and, whether a desired or undesired swing has begun, without having to con­tinuously watch the gyrocompass. The fathometer provides the soundings that the mariner needs to predict when a ship might become difficult to handle due to shoaling, and to know the clearance beneath the keel. Squat can then be antici­pated as well as the need to reduce speed as bottom clearances change. The development of the digital fathometer mounted on the forward bulkhead of the wheelhouse to supplement the recording fathometer in the chartroom has done much to increase shiphandling safety. The fathometer seems to often be forgotten once the pilot is aboard,this is unfortunate since the depth of water is basic ship handling.
Due to the mass of today's larger ships and the greater height from the water at which the pilot is now working, it has become more difficult to detect an error in judgment and to recover from that error. It is important to have an accurate means of determining the ship's move­ment-both ahead and astern over the bottom, and her lateral motion at the bow and stern.

On larger ships and ships with restricted visibility from the bridge, such as containerships, it is important to have a rate-of-turn indicator to enable the mariner to detect and control the ship's rate of swing in a turn. A rate-of-turn indicator usually supplies turn information in tenths of a degree per second, although degrees per minute are used occasion­ally, showing a rate to the right or left which corresponds to the direction of the movement of the ship's bow. It is the relative indication that is important that is whether the rate is increasing or decreasing, and by what amount. It is both inter­esting and instructive to watch a helmsman do his first trick aboard a ship fitted with a rate-of-turn indicator. After a short time, he begins to steer by using the indicator, as well as watching the jackstaff move across a point of reference as helmsmen have done for centuries. While holding the ship steady on a compass heading the rudder is used to keep a zero rate of swing. As soon as swing is indicated the helmsman uses suf­ficient rudder to check that swing, often applying the rudder before any movement of the bow to the right or left can be detected by eye.

When a ship is directionally unstable due to her hull form or trim, the rate-of-turn indicator becomes important, making it possible to navi­gate restricted channels safely. By accurately knowing the rate of turn the shiphandler can limit that rate to a known safe maximum and always keep the ship under control.