Bridge equipment Flashcards
• When to check a compass
Each magnetic compass should be properly always adjusted and its deviation card available.
Magnetic compasses should be adjusted when:
• They are first installed;
• They become unreliable;
• alterations that affect its permanent and induced magnetism;
• Electrical or magnetic equipment close to the compass is added, removed or altered;
• Every two years since the last adjustment
recorded deviations are excessive or when the compass shows physical defects.
• What is a pelorus
Compass for taking bearings over an arc of the horizon of 360 degrees.
• TMHD what is it
Transmitting Magnetic Heading Device (TMHD)94
A TMHD is an alternative to the magnetic compass required back-up power supply in the event of failure of the main electrical supply.
A TMHD is an electronic device uses the geomagnetic field to obtain and transmit the ship’s heading.
Transmitting magnetic heading devices (TMHDs) may comprise of:
• A standard magnetic compass
• An electromagnetic compass
• Explain an Echo sounder
All vessels should be fitted, used to measure the available depth of water.
From a transducer a pulse of sound is transmitted towards the sea-bed and reflected back. Given the speed of sound in water (usually 1500 m/s) and the time between transmission and reception, the depth may be calculated.
An Echo sounder shall be calibrated on each of the following occasions:
• On completion of a refit
• When any part of the equipment is changed
• If there is doubt about accuracy
• Annually
Errors of an Echo sounder:
• Shoals of fish
• Layers of water
• Underwater springs
• Seaweed
• Side echoes
• Turbulence
• Electrical faults
Waterline Depth v. ‘Keel’ Depth
The pulse from the transmitting transducer is picked up almost instantaneously by the receiving transducer and is displayed on the screen
Waterline Depth. If the transmission mark is set to the distance of the transducers below the sea surface, the recorder will show the depth of water below. The logic is that displaying waterline depths makes for easy comparisons with charted depths, provided allowance is made for the height of tide.
‘Keel’ Depth. If the transmission mark is set to zero of the scale, depth is recorded below the transducers. If the transducers are level with the keel, this depth may be considered as the ‘keel depth’. If they are not level, a further adjustment will be necessary.
Echo Sounders should be checked against the hand leadline.
• When to check an echo sounder
Echo Sounders should be checked against the hand leadline. An Echo sounder shall be calibrated on each of the following occasions:
• On completion of a refit
• When any part of the equipment is changed
• If there is doubt about accuracy
• Annually
• STW log
Paddle Wheel Type
Electromagnetic Log
Doppler log
Pitot-Static Log
• SOG Log
Doppler Log
• What is AIS
AIS is a maritime mobile VHF broadcast system that can send both dynamic and static ship information, such as MMSI, call sign, position, course and speed, to other AIS transponders and base stations.
Carriage and Usage Requirements
• All ships of 300 gt and upwards-engaged on international voyage.
• Cargo ships of 500 gt and upwards not engaged on international voyages and all
passenger ships.
Use of AIS in Navigation
- decisions should be taken based primarily on visual and/or radar information.
- There is no provision in the COLREGs for use of AIS information
• The use of VHF to discuss action is discouraged.
Decisions on collision avoidance should be made strictly according to the COLREG
Can you use AIS for Collision Avoidance Situations
The potential of AIS as an anti-collision device is recognised and AIS may be recommended as such a device in due time.
Nevertheless, AIS information may be used to assist in collision avoidance decision-making. When using the AIS in the ship-to-ship mode for anti-collision purposes, the following cautionary points should be borne in mind:
• AIS is an additional source for navigational information. AIS does not replace, but supports, navigational systems such as radar target-tracking and VTS.
• The use of AIS does not negate the responsibility of the OOW to comply, at all times, with the Collision Regulations.
• What is AIS
Consideration should be given to fitting a suitable Class “A” Automatic Identification System (AIS) transceiver to vessels that operate in areas that use AIS as part of the area safety management.
AIS is a maritime mobile VHF broadcast system that can send both dynamic and static ship information, such as MMSI, call sign, position, course and speed, to other AIS transponders and base stations.
Carriage and Usage Requirements
• All ships of 300 gt and upwards-engaged on international voyage.
• Cargo ships of 500 gt and upwards not engaged on international voyages and all
passenger ships.
Use of AIS in Navigation
AIS provides identification of targets together with the static and dynamic information.
Mariners should, however, use this information with caution noting the following important points:
• Collision avoidance must be carried out in strict compliance with the COLREGs. There is no provision in the COLREGs for use of AIS information therefore decisions should be taken based primarily on visual and/or radar information.
• The use of VHF to discuss action to take between approaching ships is fraught with danger and still discouraged. (See MGN 324 (M+F) – Radio: Operational Guidance on the Use of VHF Radio and Automatic Identification Systems (AIS) at Sea).
MCA’s view is that identification of a target by AIS does not remove the danger.
Decisions on collision avoidance should be made strictly according to the COLREGs
• Not all ships will be fitted with AIS, particularly small craft and fishing boats. Other
floating objects which may give a radar echo will not be detected by AIS.
• AIS positions are derived from the target’s GNSS position. (GNSS = Global
Navigation Satellite System, usually GPS). This may not coincide with the radar
target.
Inherent Limitations of AIS
The officer of the watch (OOW) should always be aware that other ships, and in particular leisure craft, fishing boats and warships, and some coastal shore stations including Vessel Traffic Service (VTS) centres might not be fitted with AIS. The OOW should always be aware that other ships, fitted with AIS as a mandatory carriage requirement, might switch off AIS under certain circumstances by professional judgement of the Master.
Navtex
The NAVTEX receiver is a Narrow Band Direct Printing (NBDP) device operating on the frequency 518 kHz and is a vital part of the Global Maritime Distress and Safety System (GMDSS).
It automatically receives Maritime Safety Information such as Radio Navigational Warnings, Storm/Gale Warnings, Meteorological Forecasts, Piracy Warnings, Distress Alerts.
The information received is printed on the receiver’s own paper recorder roll. Each message begins with a start of message function (ZCZC). This is followed by the text of the message and ends with an end of message function (NNNN).
The NAVTEX system broadcasts COASTAL WARNINGS that cover the area from the Fairway Buoy out to about 250 nautical miles from the transmitter; the transmissions from some transmitters can be received out to 400 nautical miles and even further in unusual propagational conditions.
The practical advice will help to ensure that you make the most efficient use of your NAVTEX receiver, guaranteeing the reception of Maritime Safety Information within the respective coverage areas of the NAVTEX stations being used.
For a NAVTEX receiver to function effectively, the operator must have a sound knowledge of how to programme and operate his particular receiver. This is not difficult, provided the following practical steps are followed:
• Make sure that there are sufficient rolls of NAVTEX paper on board.
• Check that there is paper in the receiver.
• Turn the NAVTEX receiver on at least four hours before sailing, or better still, leaves
it turned on permanently. This avoids the chance of losing vital information that
could affect the vessel during its voyage.
• Make sure that the Equipment Operating Manual is available close to the
equipment, paying particular attention to the fact that your equipment may be
programmed differently from other makes and models.
• Have available next to the equipment a plasticised copy of the
NAVAREAs/METAREAs in which the vessel is likely to sail, showing the NAVTEX stations, their coverage ranges, their respective time schedules and B1 characters.
Programme your receiver to accept only those messages identified with the B1
character of the NAVTEX station which covers the area in which your vessel is
currently sailing and the one covering the area into which you are about to sail. This
will avoid the equipment printing information which has no relevance to your voyage
and will avoid unnecessary waste of paper.
Programme your receiver to accept only those messages identified with the B2 characters (type of message) you wish to receive. It is recommended that most B2 characters (A to Z) be programmed, but you may exclude those for navaid equipments (Decca or Loran for example) with which your vessel is NOT fitted. Be aware that the characters A, B and D MUST be included, as they are mandatory.
• If information is received incomplete/garbled, inform the relevant NAVTEX station, giving the time of reception (UTC) and your vessel’s position. By so doing, not only will you obtain the information you require, but you will also help to improve the system. In the same way, any safety-critical occurrences observed during the voyage must be passed immediately to the nearest (or most convenient) Coast Radio Station and addressed to the relevant NAVAREA/METAREA or National Co-ordinator responsible for the area in which you are sailing.
