Sextant App

[SeanPatrick]

The suite of apps I mentioned in post #32 does all that and more on Android.

[davil]

[QUOTE=SeanPatrick;3688972]


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Hi SeanPatrick
is this gizmo from Amazon worth? for its intended use, adjusting declination.
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Sun Company ProSight Sighting Map Compass with Adjustable Declination - Lightweight Orienteering Baseplate Compass for Hiking, Backpacking, and Survival Navigation | Professional Grade Compass $ 39.
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thank you very much
David

[GrowleyMonster]

[QUOTE=davil;3720217]

Originally Posted by SeanPatrick

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Hi SeanPatrick
is this gizmo from Amazon worth? for its intended use, adjusting declination.
-------------------------------------------------------------
Sun Company ProSight Sighting Map Compass with Adjustable Declination - Lightweight Orienteering Baseplate Compass for Hiking, Backpacking, and Survival Navigation | Professional Grade Compass $ 39.
--------------------------------------------

thank you very much
David

Depends on what you want to use it for. Declination in land navigation refers to variation, the difference between magnetic and true North. What the adjusment does, is allow you, in the absence of ferrous, electrically charged, or magnetic objects nearby, to adjust out the variation so that the compass reads in True rather than Magnetic, as long as you remain in the same geographic area. On a vessel you must also deal with Deviation, which is the deflection of the compass needle caused by the above mentioned influences, and it is not the same at all points of the compass. Generally, at sea, you will construct a deviation table, and apply both variation, and deviation, to convert back and forth between Magnetic and True.

You can use that compass, or any reasonable quality mirror type or lensatic type compass to shoot the sun's azimuth, which can be compared to its calculated azimuth for total compass error, and the variation and deviation applied, as a check of the compass for new error. Or you can assume that it is correct and calculate your deviation for future reference. However, if you have a full size compass and a bearing circle, you can get a much more accurate azimuth. In the morning and evening you can also shoot the sun's azimuth at the correct time for an amplitude, which is much simpler math than working through solving a spherical triangle. Or even using sight reduction tables.

If you want to navigate your boat with that compass, I suggest you get two or three of them, since they are so cheap. You will find that flat pack undamped compasses used for land navigation can be very fiddly at sea, with the boat bobbing around all over the place. A proper boat compass is much better, and as a bonus, you can adjust much of your deviation out, so a simple mental addition or subtraction of variation will give you true or magnetic from the opposite.

If you are serious about navigation, you need to be serious about your compass and your heading, and course to steer, and all the things that effect your Course Made Good and Speed Made Good, so you can keep a good DR. That is the cornerstone of true navigation. If you are not serious about navigation, no worries. You will get somewhere, sooner or later, and if it is the wrong place, just try again. Or follow the little arrows on the magic display that tells you where to go. OCPN on tablet works just as good as a $1k chart plotter, if you are budget constrained. CM93 is floating around out there, and charts for US waters are free. Millions of sailors out there have never in their life done a compass correction problem, and most of them do not cause maritime disasters or get their face and boat on a milk carton or a TowBoat US ad.

It's all about how serious you are and how closely you want to follow professional level navigation practices. Prudent? Or Laissez Faire? Your call.

Though it be very dry reading, no navigator's bookshelf is complete without a copy of Bowditch. EVERYTHING is in there, at least in skeletalized form. It is a good tome to begin studying, and there are also other, easier to follow books out there, for when you have a hard time understanding just what old Nathaniel meant by this or that.

[davil]

[QUOTE=GrowleyMonster;3720277][QUOTE=davil;3720217]
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Hi GrowleyMonster

thank you for taking the time

Actually I am not interested on deviation at this time, giving the last series of reported SAR etc it picked my interest to find my old sextant and re visit its use

Referencing my old notes to calculate "declination" and because of my laziness found this gizmo that perhaps will save me a fraction of a minute to open and read the tables.

Not a biggie really but since is there and the price is right.

PS

when I say not interested on deviation,I mean only in my narrow question regarding the use of the sextant to determine Lat, we all know the importance to correct for deviation when using our paper charts.

Mahalo plenty