Annex - Position Fixing Accuracies

• Radar
• Radio D.F.
• Echo Sounder
• Visual Fixing

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1 Radar

1.1 Twenty­four miles should be considered as the maximum range for radar position fixing in a routing system. This maximum range should be used with caution, reduced in doubtful cases and only increased where local experience has positively determined a greater distance.

1.2 The errors to be taken into consideration when assessing the fixing accuracy of a radar should be

• ranging error 1.5%,
• bearing error ±1°.

2 Radio D.F.

2.1 Radio D.F. may supplement radar as a fixing device. In areas outside the effective range of radar, D.F. is to be treated as the prime navigational aid and routes should be designed to make the best use of D.F. taking into account its limitations, particularly "coastal error".

2.2 The range and bearing error to be taken into consideration when assessing the fixing accuracy of D.F. should be

• range as published in the Radio Aids to Marine Navigation,
• bearing error ±1°.

3 Echo Sounder

3.1 The design of the route should also take into consideration the practical use of an echo sounder as a supplementary positional check.

3.2 The errors to be taken into consideration when assessing the accuracy of the echo sounder should be

• ±1 metre on the shallow range scales,
• ±5 metre on the deep range scales,
  or
• ±5% of the indicated depth, whichever is the greater.

4 Visual Fixing

4.1 The routes should be designed so that the best use can be made of visual fixing as a supplement to other methods.

4.2 The errors to be taken into consideration when assessing the accuracy of visual bearings

• ±1° when using a gyro compass,
• ±1° when using a magnetic compass.

This includes allowance for personal error and assumes compasses are frequently checked in accordance with good practice and the compass bearings have been corrected for known errors.

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