Performance Standards for Devices to Measure and Indicate Speed and Distance (Speed Log)

SOLAS Requirements of Devices to Measure and Indicate Speed and Distance

SOLAS requires all ships of 50,000 GRT and above to be fitted with a speed and distance measuring device fulfilling SOLAS regulation V/19.2.3.4 and, in addition, a speed and distance measuring device fulfilling regulation V/19.2.9.2.

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SOLAS Requirements for Speed Log

Performance Standards for Devices to indicate Speed and Distance:

  • came into force in Jan 1997, as Resolution A.824 (19),
  • later got amended by MSC/Res.96 (72) in July 2002, and
  • again amended by MSC/Res.334 (90) in July 2014.

Performance Standards recommended by MSC/Res.334 (90) are as follows:

  • Devices to measure and indicate speed and distance are intended for general navigational and ship maneuvering 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 the 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 the water of depth greater than 3 meters beneath the keel. Devices measuring speed and distance over the ground should meet the performance standard in the water of depth greater than 2 meters beneath the keel.
  • Radar plotting aids/ track control equipment requires a device capable of providing speed through the water in the fore and aft direction.
  • 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.

Also Read, Auto Pilot- Working, Use, Advantages, Limitations, Tests

Methods of Presentation

  • Speed information may be presented in either analog or digital form. Where a digital display is used, its incremental steps should not exceed 0.1 knots. Analog 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.
  • 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.
  • The display should be easily readable by day and by night.
  • Means should be provided for transmitting measured speed and distance run information to other equipment fitted onboard. In this regard:
    • the information on all the speed and distance parameters, including direction, should be transmitted in accordance with the relevant international marine interface standard footnote; and
    • 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 every 0.005 nautical miles run.
  • 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.
  • 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.

Accuracy of Measurement

  • 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:
    • for a Digital Display- 2% of the speed of the ship, or 0.2 knots, whichever is greater;
    • for an Analog 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.
  • 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.
  • 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.

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 ± 10º and pitching up to ± 5º.

Constructions and Installation

  • 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.
  • 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.
  • 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.
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