Recommendation on Performance standards for devices to measure and
indicate speed and distance
1 - Introduction
1.1 Devices to measure and indicate speed and distance
are intended for general navigational and ship manoeuvring use. The
minimum requirement is to provide information on the distance run and the
forward speed of the ship through the water or over the ground. Additional
information on ship's motions other than in the forward axis may be
provided. The equipment should comply fully with its performance standard
at forward speeds up to the maximum speed of the ship. Devices measuring
speed and distance through the water should meet the performance
standard in water of depth greater than 3 m beneath the keel. Devices
measuring speed and distance over the ground should meet the performance
standard in water of depth greater than 2 m beneath the keel.
1.2 Radar plotting aids/track control equipment require
a device capable of providing speed
through the water in
the fore and aft direction.
1.3 In addition to the general requirements in
resolution A.694(17), devices to measure and
speed and distance should comply with the following minimum performance
2 - Methods of presentation
2.1 Speed information may be presented in either
analogue or digital form. Where a digital display is used, its incremental
steps should not exceed 0.1 knots. Analogue displays should be graduated
at least every 0.5 knots and be marked with figures at least every 5
knots. If the display can present the speed of the ship in other than the
forward direction, the direction of movement should be indicated
2.2 Distance run information should be presented in
digital form. The display should cover the range from 0 to not less than
9999.9 nautical miles and the incremental steps should not exceed 0.1
nautical miles. Where practicable, means should be provided for resetting
a readout to zero.
2.3 The display should be easily readable by day and by
2.4 Means should be provided for transmitting measured
speed and distance run information to other equipment fitted on board. In
- the information on all speed and distance parameters, including
direction should be
transmitted in accordance with the
relevant international marine interface standards1;
- additionally, when the equipment is used for measuring forward speed,
information may be transmitted using closing
contacts and, if so, this should be in the
form of one
contact closure each 0.005 nautical miles run.
2.5 If equipment is capable of being operated in either
the "speed through the water" or "speed over the ground" mode, mode
selection and mode indication should be provided.
2.6 If the equipment has provision for indicating speeds
other than on a single fore and aft direction, then both the forward and
athwart speeds should be provided either through the water or over the
ground. Resultant speed and direction information may be provided as a
display selectable option. All such information should clearly indicate
the direction, mode and validity status of the displayed information.
3 - Accuracy of measurement
3.1 Errors in the measured and indicated speed, when the
ship is operating free from shallow water effect and from the effects of
wind, sea bottom type, current and tide, should not exceed the
- for a digital display - 2% of the speed of the ship, or 0.2 knots,
whichever is greater;
- for an analogue display – 2.5% of the speed of the ship, or 0.25
knots, whichever is greater; and
- for output data transmission – 2% of the speed of the ship, or 0.2
knots, whichever is greater.
3.2 Errors in the indicated distance run, when the ship
is operating free from shallow water effect and from the effects of wind,
sea bottom type, current and tide, should not exceed 2% of the distance
run by the ship in 1 h or 0.2 nautical miles in each hour, whichever is
3.3 If the accuracy of devices to indicate speed and
distance run can be affected in use by certain conditions (e.g. sea state
and its effects, water temperature, salinity, sound velocity in water,
depth of water under the keel, heel and trim of ship), details of possible
effects should be included in the equipment handbook.
4 - Roll and pitch
The performance of the equipment should be such that it
will meet the requirements of these standards when the ship is rolling up
to ± 10° and pitching up to ± 5°.
5 - Construction and installation
5.1 The system should be so designed that neither the
method of attachment of parts of the equipment to the ship nor damage
occurring to any part of the equipment which penetrates the hull could
result in the ingress of water to the ship.
5.2 Where any part of the system is designed to extend
from and retract into the hull of the ship, the design should ensure that
it can be extended, operated normally and retracted at all speeds up to
the maximum speed of the ship. Its extended and retracted positions should
be clearly indicated at the display position.
5.3 If ships are required to carry
speed logs measuring speed through the water and speed over the ground,
these speed logs should be provided by two separate devices.
1 Refer to IEC Publication 61162