Celeistial Tips & Hacks
Below find a growing number of hands-on tips for making celestial navigation easier or to pass your Yachtmaster Ocean exam in style.
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How to perform a Compass Check with a bulkhead-mounted compass?
A compass check is an essential safety-check, e.g. when you have had a direct or indirect lighting strike. Who knows what your compass is showing then? Remember: a deviation of no more than 5° means that you would be off course by as much as 5 nm after having sailed for no more than 60nm.
A reliable compass is crucial if your electronic navigation becomes skanty. And classic navigation is increasingly becoming important again with the risk of jamming or spoofing satellite based navigation (GNSS) by hostile military forces.
Surprisingly enough, even expensive large yachts, advertised for world-wide ocean sailing do not always have a horizontally pedestal-mounted compass any longer, something was a matter of course in the past. The central needle’s shadow is used to determine your deviation.
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The shadow of the central needle is giving you the compass reading of the Azimuth (bearing of the sun). Considering the magnetic variation, the compass deviation is easily found and the compass can be checked.
The ones who have a white compass rose are even better off, since a shadow against a white background is, of course, much easier to read.
Regina Laska’s new compass before installation has a white compass rose for easier observing the shadow. This is a photo taken in the Cassens&Plath workshop, so hence no shadow!
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But how about boats with a bulkhead mounted compass or a compass over the companionway or, beware, even mounted under the table! How do you perform a compass check, here, one might ask!?
Can you find the compass? Hint: It’s the only unlit instrument on the photo!
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Or how about this compass? Purely electronic! If you didn’t see it, iths the central vertical display with a picture of a red “compass rose” simulating you see it from the side (it’s much easier to steer according to a compass you see from above, by the way).
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Next riddle: can you find the magnetic compass on the below yacht offered for EUR 6 Mio at the recent boot Düsseldorf? Let alone checking it’s accuracy on the ocean?
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Now for all of you, who have a compass with no usable central needle for checking the compass deviation: Do not dispair! There is a small hack!
First go to your local grocery store and buy some bamboo skewers. Make sure the tops are milled to a sharp needle or sand it down yourself. Now cut it to the desired length so it gives a nice sharp shadow on the specially developed Cassens&Plath beer mat / Coaster. On the backside of the compass rose you find the picture of a small white screw in the center. This is where you stick through your wooden skewer.
How to perform a compass check without a compass at the pedestal:
- Sail in an as straight line as possible in as little waves as possible.
- Turn the beer mat so that the compass heading read off your main compass corresponds to the “heading” of the beer mat. It’s easier if you place your beer mat onto something pointing parallel to the ship’s heading, e.g. put it onto your cockpit table, your teak deck seams or similar. Now it’s like turning your portland plotter!
- Read off the shadow.
- Find your compass’ deviation by taking the variation into account and compare your shadow reading with the Azimuth found in the celestial tables.
Tip: It’s easy if you make your skewer a bit longer so the underside fits into the the groove of your foldable cockpit table (which is folded up during the compass check). Now it’s easier to turn the beer mat and to read off the compass heading in the groove pointing forward.
Read off your main compass heading and turn the beer mat accordingly. In this case, the ship’s heading is 209°C according to the main compass (not shown), so turn the beer mat in the same direct.
Example:
Your ship’s main compass is showing a heading of 209°C. Now turn your beer mat so 209° is showing as a heading as well (e.g. read 209C where the table groove is). The main compass and the beer mat should now show the same “heading”.
Read off the shadow that the skewer makes on the beer mat. The shadow in this example shows 248° Compass, meaning the compass “claims” the bearing towards the sun (= “Azimuth”) is 248°-180° = 68°. And yes, it is early morning when I shot this photo, so it is true that the sun has a bearing (Azimuth) of around ENE.
Thanks to celestial navigation it is easy to calculate the true Azimuth taken off the HO248 tables. In this case, let’s assume the true Azimuth was found in the table and reads 74° True (all figures in books, tables and on the chart are true bearings, by the way).
Taking a variation of 1°W for these waters in this year into account, the compass should have shown 75°M.
But it didn’t! The remaining fault from 75°M to 68°C must be the deviation. The compass shows too little on this heading, doesn’t it? 7° to be precise. And you might remember the saying “Error East – Compass Least” meaning that the error must be easterly Deviation in this case, since the compass is showing less than it should (“less” -> “least”).
Answer: On a heading of 210°C we have a compass deviation of 7° East.
Voilà!
A couple of these readings on various courses, and you have soon collected a complete deviation table.
N.B. I admit: it is not easy to follow the main compass and turing the beer mat as quickly as the compass swings. Therefore, there is nothing better than a stable horizontal compass on the pedestal with a proper needle giving a clear shadow on a white compass rose. Full stop! The shadow then reads off the compass so easily! But at least this hack is a work-around for you to be able to demonstrate in your RYA Yachtmaster Ocean exam that you have checked your compass’ deviation by celestial navigation. This compass check is an obligatory part of the RYA Yachtmaster Ocean exam. So using the Cassens&Plath beer mat method is better than nothing and the best solution for your RYA exam lacking a proper classic compass.
Reginasailing template to find the deviation of the compass.
If you wish to learn now to find your Azimuth, there is a Reginasailing template for the compass check including how to calculate the true Azimuth. Contact me if you are interested in the template.
There is also a video on how to perform a compass check.
And don’t forget to buy your screwers in your closest supermarket and the compass check beer mats or coasters from Cassens&Plath here.
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Avoid forgetting celestial navigation
It’s less of a hack but still worth remembering:
The Reginasailing templates do not only help you guide through the calculations while learning the method of finding a fix using celestial sight reduction. They are also perfect should you forget how it works before your next sailing season! So don’t forget to order your most relevant celestial templates for the sun from Cassens&Plath (there are two for sight reduction and noon sight) as well as the practical A3 sized plotting sheets.
And if you forget how they work, there are over 12 hours of completely free videos to explain everything!
If you are interested in obtaining templates for the planets, stars and the moon, please contact me.
Using the templates facilitate remembering the individual steps. Year by year.
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Avoid chasing the sun when taking an altitude
When you shoot the sun the idea is to do several things at the same time. You need to get the sun exactly touching the horizon typically with the lower limb. Many do this by turning the micrometer on the sextant. Simultaneously, you have to make sure the sextant is exactly vertical and last, but not least, you need to decide when to shout “now!” to make a note of the absolute exact time. Four seconds off mean an whole mile off! This can be a bit difficult.
Normally, you are trying to follow the sun’s movement by turning the (red) micrometer. But there are better ways!
Instead of chasing the sun by trying to follow the movement of the sun by turning the micrometer in the same speed as the sun moves, try this instead: Turn the micrometer so you are a bit “ahead” of the sun. This means that in the morning, you turn the micrometer so the lower limb of the sun is still clearly under the horizon and in the afternoon, you turn the micrometer so that the sun is still clearly above the horizon. Then you don’t have to turn the micrometer any more.
Thereafter you make sure you hold the sextant exactly vertically. Traditionally this is done by a pendulum movement so that the sun moves from left to right. In the morning, the sun should remain under the horizon no matter how you swing and in the afternoon it remains above the horizon.
This is how you normally swing the sextant to make sure the lower limb of the sun is just touching the horizon
If you, however, have a Cassens&Plath sextant with a double prism (“Shülerprisma”) it is so much easier to know when you hold your sextant vertically. You don’t have to swing the sextant, it tells you directly!
If you are the lucky owner of a Cassens&Plath Horizon Ultra sextant, you will have a Shülerprisma which easily tells you if your sextant is vertical or not.
Now just wait until the sun has risen just enough so the lower limb touches the horizon without moving the micrometer in the morning or until the sun is low enough to do the same.
When the sun just “kisses” the horizon, shout “now” and your friend eagerly watching the chronometer will note the time.
Make yourself comfortable and just wait until the sun get’s where it should.
Noting the time in the correct order
First note down the seconds (which change the fastest), thereafter the minutes and last the hours. If you note the hours first you might have forgotten the number of seconds by the time it’s time to write them down.
Write from right to left so it still shows hh:mm:ss but note them in the reverse order.
Impossible to forget the seconds? Well, seasickness and tiredness can do all sorts of jokes and better safe than sorry! And the navigator will not be please if you reveal your lacking memory by saying: “what did you say the seconds were…?”
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Anita waiting for Markus to shoot Venus and to shout “now” when the planet just touches the horizon (being a dot there is no upper or lower limb for planets or stars, by the way)
Uncertain which sextant to buy?
Check out the Reginasailing tips on various brands and varieties of sextants here.
Don’t forget the Reginasailing discount you get on Cassens&Plaths sextants and any books such as Almanacs from Bookharbour.com.
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