Rate of Turn Indicator
- IMO Recommendations on passage planning lay stress on controlled navigation. The passages in narrow channels or harbors are either along straight courses or along arcs of circles.
- As per SOLAS 2000 Amendment Chapter V Regulation 19.2.9, it is mandatory for ships over 50,000 GRT to have a rate of turn indicator. IMO recommends that large alteration of courses have to be planned along circular tracks with wheel over point marked.
- The Rate of Turn Indicator (ROTI) is a device which indicates the instantaneous rate at which the ship is turning. It is fitted on ship as an independent fitment integrated with the steering gear/auto pilot.
- When the wheel is turned over, the ship actually traverses along a curved track rather than performing a sharp turn about a point. It is very useful knowing the nature of this traversed path the ship takes which can help in planning:
- The desired turn with given radius
- Desired speed of the vessel to execute the planned turn.
- When to apply the turn (wheel over point).
RATE OF TURN FORMULAE:
ROT = v/R
v – Speed of the vessel .
R – Radius from a fixed point around which to turn the ship.
Note: ROT is directly proportional to the speed.
ROT is inversely proportional to radius.
Use of ROTI (Rate Of Turn Indicator):-
- The rate of turn indicator is equipment which indicates the instantaneous rate at which the ship is turning.
- This indicator is fed 60 to 200 pulses per minute from the steering repeater and from this input it works out the instantaneous rate of turn.
- The dial is marked usually 0O to 60O on either side. As per IMO performance standard the dial should be marked not less than 0O to 30O per minute on either side and graduated in intervals of 1O per minute.
- As we know that when ship turn she actually traverses some distance round the arc of a circle and cannot execute a sharp turns about a point.
- When ship is making a turn it precise the ship track uncertain due to her characteristic, condition, weight and UKC.
- Therefore navigator uses the touch of ship track during the turn that is uncertain of position until the ship is steadied on the new course.
- IMO recommends for passage planning is not only monitor the position on straight course but also on curve section of passage. This can be achieved by the technique called radius turn by the help of roti and ship’s log.