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Compass Bearings

Cross bearing

We can determine our estmated position by means of a cross-bearing. We make a compass bearing of a point that we can recognize both on the map and along or on the water. We convert this compass bearing into a true bearings. We draw that bearing on the chart as a line to the point on the chart. We then know that we are at least on that line. We just don’t know where on that line yet. So we need a second bearing line at another recognizable point. The intersection of two bearing lines is our position. It is important that we make the angle between the two bearings as perpendicular as possible, through the correct choice of recognizable bearing objects. Otherwise the bearing is not reliable. It is even better to make 3 bearings. If the 3 lines on the map do not pass through approximately the same point, something is wrong. When we make a bearing, don’t forget to account for the variation and deviation (only if the bearing is made on the steering compass). If we make the bearing with the hand bearing compass, we assume that the deviation is 0, because we do not have a deviation table for the handheld compass.

kruispeiling

Luminous range diagram

The nominal range of a lighthouse can be found in the list of lights and in the chart. That nominal range applies at a visibility of 10Nm. If visibility is better, then a light can be seen from a greater distance. That distance/range determined by visibility is called the “luminous range” and we can look it up in the chart below.

If you were to draw a vertical line at the nominal load of 12Nm to the graph of 10Nm visibility and from that intersection point draw a horizontal line to read the luminous range, you will immediately notice that luminous range is equal to the nominal load, which is 12Nm. This is because the nominal range applies at 10Nm visibility.

luminous range diagram

Example 1: Luminous range

Suppose a lighthouse has a nominal range of 18Nm. The visibility is 20Nm. What is the luminous range?

Answer: 30Nm

Example 2: Luminous range

Suppose you want to use a light to make a bearing and need a luminous range of 5Nm to do so. The nominal range of the light is 6Nm. What is the minimum visibility you need to make a bearing on the lighthouse?

Answer: minimum 7.5 Nm

Bearing to stay clear of hazards

Background bearing

For example: if you just can no longer see between two islands, you know which line in the map you are on. A light line or guide line is also a kind of background bearing. So if you see on the chart that it is safe sailing on a line of 2 points that are in line with each other, you can use that background bearing to stay clear of hazards.

NMT or NLT

We can also draw a bearing line on 1 object in the map that separates a safe and a hazardous sector. We then determine whether the bearing

    • should not be more than x degrees (No more than)

    • should not be less than x degrees (no less than)

To stay in safe waters. We note NMT or NLT at the bearing line in the chart.

Questions & Answers

Question 1: You are sailing off the coast of Walgeren. Your compass course is 88°. Your compass bearing is 183°. What is your true bearing?

a: 171
b: 176
c: 185

Question 2: You are sailing off the coast of Walcheren. Your compass course is 245. Your compass bearings are 160 and 59. What are your true bearings?

a: 147° and 46°
b: 142° and 49°
c: 141° and 40°

Question 3: You sail a compass course of 25° in front of the Maasmond in the direction of Scheveningen. You make a bearing on the northern pier of the Maasmond on compass bearing 170. You are making another bearing on the lighthouse of Scheveningen with bearing 88 What is your fix?

a: 52°03.4’N and 004°00.4’E
b: 51°03.4’N and 004°0
c: 52°03.4’N and 004°00.0’E

Question 4: You sail a compass course of 90° and make a bearing on the church tower of Goedereede in line with the church tower of Stellendam. (Both on Goeree). You will also make a bearing on the lighthouse of West Schouwen (on Schouwen) on compass bearing 213°. What is your fix?

a: 51°50.5’N 003°50.6’E
b: 51°49.5’N 003°40.6’E
c: 51°51,5’N 003°48,4’E

Question 5: You sail in the Roompot (above Walcheren) towards the Roompot locks on a compass course of 110°. You make a bearing on the lighthouse of Westkapelle with compass bearing: 207°. You make a bearing on the church tower of Oostkapelle on Compass bearing: 152°. What is your fix?

a: 51°36.8’N and 003°30.0’E
b: 51°30.2’N and 002°30.1’E
c: 51°33.8’N and 003°31.0’E

Question 6: You are sailing exactly on the leading lights to Westkapelle and want to determine your fix by a cross-bearing on a second object. Which object is best to use for this?

a: the church tower of Domburg
b: the lighthouse of West Schouwen
c: the church tower of Middelburg

Question 7: Your compass course is 95°. Let’s assume that the ground course is also 95° and the ground speed is 4.8 knots. You make 2 bearings on Goeree platform. (ca. 51°55.4’N and 003°40.0’E). Compass bearing 1: 38° and compass bearing 2: 334°. What is your fix at the time of the second bearing?

a: 50°51.5’N and 003°44.4’E
b: 51°52.5’N and 003°43.0’E
c: 51°51.5’N and 003°44.4’E

Question 8: The height of a lighthouse whose light is visible just above the horizon, 49 meters. Height of the eyes above water is 2 meters. What is the distance to that light in nautical miles?

a: 19.7 Nm
b: 17.7 Nm
c: 15.5 Nm

Question 9: At how many miles away do you lose sight of the Scheveningen lighthouse (2 flashes in 10 seconds, see nautical chart) if your eyes are 4 meters above water?

a: 18.9Nm
b: 15.7Nm
c: 20.1Nm

Question 10: What causes you to lose sight of the lighthouse in the first place, due to the limited geographical range at an eye height of 4 meters or due to the limited nominal / optical range (the strength of the lamp)? Due to the limited:

a: Optical range
b: Nominal range
c: Geographical range