Education of coastal navigation always includes some trigonometry for figuring distance off. Taking an angle of a lighthouse or some other structure and doing the math to see how far away it is located. Or maybe doubling the angle off the bow an knowing that the distance off is the distance traveled between the two sightings. My question is ; does anyone do this?? I usually just follow a contour line with my depth sounder or use eyeball navigation. You know if there is something on the right side to avoid I get on the left side. If it's deeper in the middle I stay there. Again I know many keep their eyes glued to the GPS but for those that don't how do you stay off of the rocks??
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I like to pull the sextant out for practice
And determine my distance from a bridge or tower of known height. With a calculator it is a simple calculation. Ay one of my anchorages there is a water tower to the NE and a light house to the west. If I take a bearing on each and plot the intersect I can pinpoint my position if I can see only one With the sextant I can get distance and with the hand bearing compass I get direction and can dertermine my position . Then I check to see if the GPS is still working.
And determine my distance from a bridge or tower of known height. With a calculator it is a simple calculation. Ay one of my anchorages there is a water tower to the NE and a light house to the west. If I take a bearing on each and plot the intersect I can pinpoint my position if I can see only one With the sextant I can get distance and with the hand bearing compass I get direction and can dertermine my position . Then I check to see if the GPS is still working.
Various 'calcs' .....
Easiest/quickest: I have a military hand bearing compass ... and simply triangulate the position graphically on a paper or electronic chart. Alternatively if you know how to do trigonometry calcs. and have a binocular with a vertical degrees scale included within the optics: ArcTan = distance to object / height of object; distance to = height / arctan of the angle. Or if you have a sextant, ditto. All this works well especially in those places that have shifty bottoms that will not allow accuracy of depth sounders.
Easiest/quickest: I have a military hand bearing compass ... and simply triangulate the position graphically on a paper or electronic chart. Alternatively if you know how to do trigonometry calcs. and have a binocular with a vertical degrees scale included within the optics: ArcTan = distance to object / height of object; distance to = height / arctan of the angle. Or if you have a sextant, ditto. All this works well especially in those places that have shifty bottoms that will not allow accuracy of depth sounders.
I don’t yet have a GPS
Tom, I don’t yet have a GPS and my navigation so far is by traditional ways using a tafrail log, compass, handbearing compass, sextant and hand lead. After using a friends GPS to make a landfall at Bermuda last year I will buy one but as of now I have not done that. I don’t often take out the sextant while on soundings but I have under some circumstances. For the most part a hand bearing compass and tafrail logs have been sufficient. And yes I do use the various tricks such as doubling the angle and using distance run to tell how far off a point I am. All the best, Robert Gainer
Tom, I don’t yet have a GPS and my navigation so far is by traditional ways using a tafrail log, compass, handbearing compass, sextant and hand lead. After using a friends GPS to make a landfall at Bermuda last year I will buy one but as of now I have not done that. I don’t often take out the sextant while on soundings but I have under some circumstances. For the most part a hand bearing compass and tafrail logs have been sufficient. And yes I do use the various tricks such as doubling the angle and using distance run to tell how far off a point I am. All the best, Robert Gainer
I have a calculator and Binoculars with angles
The biggest problem with angles is that the angles get really small unless the object is really tall. I have done most of the navigation tricks as an exercise to practice skills. But normally I am lazy. I have a trigger depth usually about 15-20' and check the chart for areas that are less than these depths and avoid those areas. Sailing coastal I do the same but deeper at night. Say 50' if it gets less than that I head south(going along the gulf coast). During the day I just keep the coastline low on the horizon. So Ross exactly why do you need to check your location accurately in your anchorage?? I do take a couple bearings with the compass on landmarks to make sure I am not drifting but never actually figure out my exact location on the chart. In the lake I usally know that I am between my anchor and a tree that I've tied to on shore. Again I'm trying to figure out what most of us routinely do. Robert saying that he doesn't use the sextant once on soundings makes me wonder if he is navigating by depth. Knowing that the channel from a bays entrance often extends miles to sea a triggering depth to stay in that channel should work. Say you know that the entrance to chesapeak bay is at the end of such a channel and that getting into water less than 100' means that you are missing the entrance. So head west and then north or south to stay in the deeper water until you start seeing buoys. Does anyone use RDFs??? A conviently located radio station is how the Japanese found Pearl Harbor back in 41.
The biggest problem with angles is that the angles get really small unless the object is really tall. I have done most of the navigation tricks as an exercise to practice skills. But normally I am lazy. I have a trigger depth usually about 15-20' and check the chart for areas that are less than these depths and avoid those areas. Sailing coastal I do the same but deeper at night. Say 50' if it gets less than that I head south(going along the gulf coast). During the day I just keep the coastline low on the horizon. So Ross exactly why do you need to check your location accurately in your anchorage?? I do take a couple bearings with the compass on landmarks to make sure I am not drifting but never actually figure out my exact location on the chart. In the lake I usally know that I am between my anchor and a tree that I've tied to on shore. Again I'm trying to figure out what most of us routinely do. Robert saying that he doesn't use the sextant once on soundings makes me wonder if he is navigating by depth. Knowing that the channel from a bays entrance often extends miles to sea a triggering depth to stay in that channel should work. Say you know that the entrance to chesapeak bay is at the end of such a channel and that getting into water less than 100' means that you are missing the entrance. So head west and then north or south to stay in the deeper water until you start seeing buoys. Does anyone use RDFs??? A conviently located radio station is how the Japanese found Pearl Harbor back in 41.
Lets try again Tom.
Tom, I don’t often use the sextant unless I am offshore or going trans-ocean but I have at times found it useful while sailing along the coast. Especially sailing along a featureless coast such as the long low sand beaches near Gambia in Africa. You could take a sun line and cross that with the shoreline on the chart and see how far you were from the harbor at the mouth of the Gambia River. A place like that doesn’t have any landmarks or navigation aides except at the harbor itself so it’s easy to sail down the coast and miss the harbor entirely. I don’t usually take vertical angles with the sextant because sights with the handbearing compass are faster and easier to get and you will almost always find more then two landmarks when you are close enough to the shore. I can take vertical angles and I have but it’s not very frequently. As Ross does I take bearings after dropping the anchor with my handbearing compass so that I can tell if I am dragging later. I plot the bearings on the chart for convenience but don’t really care where I am anchored except that I want to stay where I dropped the anchor originally. I have a depth sounder on my current boat but I don’t sail by depth. It’s too difficult to maintain a DR if you wander all over the chart. I sail from point to point and allow for set and drift. I still find my hand lead useful because it brings up a sample of the bottom. In some places the bottom is quite different from point to point matching the sample to the chart or past experience is useful. The depth sounder really is useful if I am coming into a new area and need moment by moment updates. I do not use an RDF at all now. All the best, Robert Gainer
Tom, I don’t often use the sextant unless I am offshore or going trans-ocean but I have at times found it useful while sailing along the coast. Especially sailing along a featureless coast such as the long low sand beaches near Gambia in Africa. You could take a sun line and cross that with the shoreline on the chart and see how far you were from the harbor at the mouth of the Gambia River. A place like that doesn’t have any landmarks or navigation aides except at the harbor itself so it’s easy to sail down the coast and miss the harbor entirely. I don’t usually take vertical angles with the sextant because sights with the handbearing compass are faster and easier to get and you will almost always find more then two landmarks when you are close enough to the shore. I can take vertical angles and I have but it’s not very frequently. As Ross does I take bearings after dropping the anchor with my handbearing compass so that I can tell if I am dragging later. I plot the bearings on the chart for convenience but don’t really care where I am anchored except that I want to stay where I dropped the anchor originally. I have a depth sounder on my current boat but I don’t sail by depth. It’s too difficult to maintain a DR if you wander all over the chart. I sail from point to point and allow for set and drift. I still find my hand lead useful because it brings up a sample of the bottom. In some places the bottom is quite different from point to point matching the sample to the chart or past experience is useful. The depth sounder really is useful if I am coming into a new area and need moment by moment updates. I do not use an RDF at all now. All the best, Robert Gainer
No greater/no less than bearings
While I have used all the above from time to time when that was the only way to get my position, I find that for coastal navigation the concept of a not greater than/not less than course to avoid obstacles to be the technique I use almost every time I go out. Plotting a course from my current location to the obstacle and then making sure I never sail on the other side of that course line insures that I will miss it. And don't forget to add in the set/drift correction. I also find this makes "sailing" much more relaxed as I can vary the course for wind shifts or tacks and still not have to worry about getting into trouble. Also helps the Corinthian crew who usually don't really know (or need to) where they are to the degree that say the captain should.
While I have used all the above from time to time when that was the only way to get my position, I find that for coastal navigation the concept of a not greater than/not less than course to avoid obstacles to be the technique I use almost every time I go out. Plotting a course from my current location to the obstacle and then making sure I never sail on the other side of that course line insures that I will miss it. And don't forget to add in the set/drift correction. I also find this makes "sailing" much more relaxed as I can vary the course for wind shifts or tacks and still not have to worry about getting into trouble. Also helps the Corinthian crew who usually don't really know (or need to) where they are to the degree that say the captain should.
Off many coasts the water is too deep
to follow the contour. We preplan trips and use danger bearings and cross bearings ahead of time, so we end up knowing where were are (and are not).
to follow the contour. We preplan trips and use danger bearings and cross bearings ahead of time, so we end up knowing where were are (and are not).
Eye ball
I usually eyeball my way around, using GPS when things are little tight. I do use the handbearing for frieghters and anchoring and could use it if I had no GPS. If there is a danger point I often use the GPS to avoid it, watching my lat/lon in comparison to the object. I use SeaClear chart plotting, but in Canada I have to rely on plotting my position by hand using a GPS as I have no Canadian electronic charts. I have been some places in canada, where the GPS if not accurate enough. I use contours in fog and usually keep an eye on my depth sounder if along a coast to be sure I am staying in deep enough water.
I usually eyeball my way around, using GPS when things are little tight. I do use the handbearing for frieghters and anchoring and could use it if I had no GPS. If there is a danger point I often use the GPS to avoid it, watching my lat/lon in comparison to the object. I use SeaClear chart plotting, but in Canada I have to rely on plotting my position by hand using a GPS as I have no Canadian electronic charts. I have been some places in canada, where the GPS if not accurate enough. I use contours in fog and usually keep an eye on my depth sounder if along a coast to be sure I am staying in deep enough water.
Literal Rule of Thumb
Hello, I found the information on this site very useful. Please check it out, it might be helpful to you as well. www.boats.com go to the " How To/ Tips" section, and click on "Successful Navigation", 15 tips for getting to port safely-without your GPS. Have fun, and take care, Jay
Hello, I found the information on this site very useful. Please check it out, it might be helpful to you as well. www.boats.com go to the " How To/ Tips" section, and click on "Successful Navigation", 15 tips for getting to port safely-without your GPS. Have fun, and take care, Jay
I guess that it Depends
Here on the gulf coast hotels and a few towers are about the only high things for visual reference. Bridges also come in handy. There is a good lighthouse at the entrance to Pensacola. Depth usually increases slowly from shore and is a good indicator of distance off. At Wheeler lake the main body is a mile or so wide and has a paper mill about 1/2 way up the major pool. TVA also puts mile markers along the shore so it is hard to get lost.
Here on the gulf coast hotels and a few towers are about the only high things for visual reference. Bridges also come in handy. There is a good lighthouse at the entrance to Pensacola. Depth usually increases slowly from shore and is a good indicator of distance off. At Wheeler lake the main body is a mile or so wide and has a paper mill about 1/2 way up the major pool. TVA also puts mile markers along the shore so it is hard to get lost.
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