angles relative to your vessel
February 20th 2007 03:23
Angles relative to your vessel.
We are all fairly used to using the clock as suggesting where an object is, relative to ourselves or our boat. “Object at one o’clock” someone might say and we look to the front or bow and come round to the right or starboard and look along a line reading one o’clock for the object. If however some one said to look two points to starboard, how many would know to look to starboard twenty-two point five degrees? It all gets a bit hairy, fairy and some mariners came up with a fairly accurate way to determine angles relative to your vessel. Relative to your vessel actually means using the bow or direction forward you are steering as 000deg or 360deg. (this would be north on a compass but we are not using a compass, you vessel is the compass if you like.) Now you divide the vessel up into sections. A direct right angle either side of the bow would be ninety degrees port or starboard (relative). From our steering position find and object on either side that we can site along to divide the port and starboard bow in two, giving us forty-five degrees (relative.) Split this again and you have twenty-two and a half degrees (relative) or two points off the port or starboard bow.
What does all this mean and how can we use it? Well finding distance off is one job you can easily do. Sail along in a straight line until and object you recognise on the chart is forty-five degrees relative to your vessel. Take the time and note the speed you are doing or estimate your speed. When the object is at right angles to you, again note the time. Now you can work out how far you have travelled since you saw the object at forty-five degrees. Say it was one mile. You have created a right-angled triangle with the object and yourself with you now at the right angled corner. The distance you have travelled is the distance you are off the object. {Equal distant sides of a triangle having forty-five degree angles opposite a ninety degree angle.}
You can also estimate the angle of the sun above the horizon with some accuracy. If you hold out your arm, extended directly in front of your face with the fingers of your hand and thumb closed, the angle that the exists between the outside edge of the fingers is about fifteen degrees. The sun crosses the sky at about fifteen degrees an hour. So if you place your hands alternately side by side from the horizon to the point above your head it should represent six hand spans and take you to midday. So one finger width is about three degrees of the compass or twelve minutes of the hour. This is not super accurate navigation but it will do at a pinch. You can try this around the horizon if you know the exact number of degrees an object is from north and work out a rough course without a compass. Don’t rely on this with your life! It is purely an exercise.
We are all fairly used to using the clock as suggesting where an object is, relative to ourselves or our boat. “Object at one o’clock” someone might say and we look to the front or bow and come round to the right or starboard and look along a line reading one o’clock for the object. If however some one said to look two points to starboard, how many would know to look to starboard twenty-two point five degrees? It all gets a bit hairy, fairy and some mariners came up with a fairly accurate way to determine angles relative to your vessel. Relative to your vessel actually means using the bow or direction forward you are steering as 000deg or 360deg. (this would be north on a compass but we are not using a compass, you vessel is the compass if you like.) Now you divide the vessel up into sections. A direct right angle either side of the bow would be ninety degrees port or starboard (relative). From our steering position find and object on either side that we can site along to divide the port and starboard bow in two, giving us forty-five degrees (relative.) Split this again and you have twenty-two and a half degrees (relative) or two points off the port or starboard bow.
What does all this mean and how can we use it? Well finding distance off is one job you can easily do. Sail along in a straight line until and object you recognise on the chart is forty-five degrees relative to your vessel. Take the time and note the speed you are doing or estimate your speed. When the object is at right angles to you, again note the time. Now you can work out how far you have travelled since you saw the object at forty-five degrees. Say it was one mile. You have created a right-angled triangle with the object and yourself with you now at the right angled corner. The distance you have travelled is the distance you are off the object. {Equal distant sides of a triangle having forty-five degree angles opposite a ninety degree angle.}
You can also estimate the angle of the sun above the horizon with some accuracy. If you hold out your arm, extended directly in front of your face with the fingers of your hand and thumb closed, the angle that the exists between the outside edge of the fingers is about fifteen degrees. The sun crosses the sky at about fifteen degrees an hour. So if you place your hands alternately side by side from the horizon to the point above your head it should represent six hand spans and take you to midday. So one finger width is about three degrees of the compass or twelve minutes of the hour. This is not super accurate navigation but it will do at a pinch. You can try this around the horizon if you know the exact number of degrees an object is from north and work out a rough course without a compass. Don’t rely on this with your life! It is purely an exercise.
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