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Sailing reference
Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.
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An adjustable ring you expand to measure the distance to a target
The VRM is an electronically generated circle centred on own ship whose radius is displayed numerically, and it is the most accurate measurement a radar offers. The correct technique is to touch the ring against the nearest edge of the target echo, not its centre. Most sets provide two independent markers, allowing a radar fix from two or three ranges to well-identified charted features, which is generally superior to a fix by bearings.
Read definition →The angle between true north and magnetic north at your position
Also called magnetic declination ashore, variation is the local difference between the direction of the Earth's magnetic field and the geographic meridian. It is named East when magnetic north lies clockwise of true north and West when anticlockwise. Values range from zero near an agonic line to more than 30 degrees in some regions and towards very large values near the poles. Variation changes slowly with time, typically a few minutes of arc per year, so charted values need updating.
Read definition →The three-sided plot combining boat movement, tide and resulting track
All dead reckoning problems reduce to one triangle whose sides are the water track, the tidal stream vector and the ground track. Any two known sides determine the third. Constructed for the EP, the tide vector is added to the end of the water track; constructed for course to steer, the tide vector is laid first from the start position. All three vectors must cover the same time period, and all directions must be in degrees true.
Sailing reference
Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.