1 - Introduction
1.1 Devices to measure and indicate speed and distance are intended for general navigational and ship manoeuvring use.
AlthoughThe 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 andDevices 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.
Radar plotting aids/track control equipment require a device capable of providing speed
through the water in the fore and aft direction.
1.2 1.3 In addition to the general requirements in resolution A.694(17), devices to measure and
indicate speed and distance should comply with the following minimum performance requirements.
In addition to the general requirements in resolution A.694(17), devices to indicate speed and distance should comply with the following minimum performance requirements.
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 unambiguously.
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 night.
2.4 Means should be provided for
feedingtransmitting measured speed and distance run information to other equipment fitted on board. In this regard: when contact closure is used, forward speed only should be indicated. The information should be in the form of one contact closure (or the equivalent) for each 0.005 nautical miles run; and whenthe information on all speed and distance parameters, including direction should be
transmitted in accordance with the relevant international marine interface standards1;
serial digital interface is provided, the information on all speed and distance parameters, including direction, should be provided in the form of a serial stream of digital information conforming to the international protocol for a digital interface for marine equipment use. 1
- additionally, when the equipment is used for measuring forward speed, then the
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
axisdirection, then both the , then the forward and athwart speedspeeds should be provided either through the water must be provided, and the forward and athwart speed over the ground may be provided as an additional option. Resultant speed and coursedirection information may be provided as a switchabledisplay 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 following:
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 greater.
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.
11 Refer to IEC Publication 61162 Refer to IEC 1162:1994.