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Compass Calibration- The Easy Way
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- เผยแพร่เมื่อ 17 ส.ค. 2024
- Step by step compass calibration procedures based on the Sun including calculations for constructing a Deviation Table plus examples of applying Deviation to typical navigation situations.
That's the best method I've seen in 50+ years , thank you. I'm doing it!
Also note that the Variation on the charts must be adjusted to the current year. On Old charts this can be substantial. AND the magnetic pole is moving faster than ever thanks to "blobs" in our molten iron core; yes, google that. Cheers!
If you mount the maneuvering chart 0 to the stern instead of 0 to the bow, then you can skip needing to add/subtract 180 to convert reciprocal bearings to relative bearings.
That's a good suggestion. Thanks... MDS
Nicely done! I'm in the middle of ASA 105, "Coastal Navigation and Piloting", and I tried swinging a ship's compass using the ranging method described in the course. The experience can best be described as a comedy of errors. Trying to sight the range over the compass was darn near impossible. Nonetheless, as Capt. Tursi points out, that's the method taught in most courses.
The sun-shadow method described in this video sure looks a whole lot more practical. I found a round plywood cut-out at a local craft store, and a metal rod at the Home Depot next door. I have ordered a pad of maneuvering boards, and I am looking forward to giving this method a go! Thanks, Capt. Tursi!
Thank you David... Please send us an email to office@mdschool.com if you have any specific questions as you go through this process. We'd be glad to help... T
This is an excellent video - thank you for sharing! I can't wait to use this method on my own boat. How did you find the centerline of the boat with which to align your maneuvering board? It seems like it would be fairly easy to be off 1 or 2 degrees when finding the exact centerline of the boat - throwing the deviation table out of whack for a few degrees.
So well laid out! Thank you!
Excellent video
Very good video. One quick question on setting up and placement of the "deck sundial." Does it need to be close to level fore and aft, and a
thank you
Thank you Capt. Tom! Very clever and I look forward to trying it . A couple of questions: 1) Can one use an almanac to look up the sun's bearing? Can you recommend an almanac for this, or an online source? 2) Does the geographical location of the boat (and the subsequent magnetic variation of the area) affect the compass' deviation? If we move the boat 500 or1000 miles to a new cruising ground would we need to recalibrate the compass or produce a new deviation table? Or is the deviation effect mostly or completely due to onboard interference? PS We sailed with Cap. McKee a few years ago out of Langford Creek doing 103/104-most enjoyable. We now have our self-built alloy Dix 43 on the water in N. Mississippi, about to take her down to the Gulf Of mexico in a month for her first taste of salt water!
The sun's bearing is based on date, time and your location, and therefore needs to be a calculation since an almanac does not know your location; also note that this bearing changes second by second. Deviation refers to magnetic influences within your boat and is the difference between the local magnetic north and compass north, so ideally it should not change with changes in your location as long as you are looking up Variation on an up to date local chart... Come and take an online celestial navigation course with us this winter and learn how to calculate the Sun's direction manually based on the nautical almanac
Here you have used 9 bearings to create your deviation graph. Is this generally enough or is there the possibility of non-linear fluctuation between two of these? I'm guessing that larger ships with more metal perhaps require more points to be accurate?
It's probably enough, but some people like to use 30 degree increments, which would give you 12 points. I doubt that much of significance happens between those points whether you do 30 or 45 degrees
Excelent!
awesome thankyou
I've worked through this multiple times and I'm getting lost on a point. How does the Compass Bearing to the Sun (H + RB) relate to getting the Bearing to the Sun? It seems like there is no connection between these two numbers. The Bearing to the Sun comes from the calculation of Lat./Long. + Date/Time. What was the purpose of spinning my boat around the compass other than to get the time I was at each cardinal point? (I must have watched this video at least a 100 times and I still don't get it - I must be denser than most. Sorry.)
G'day Lucas,
The Magnetic compass heading + Relative bearing gives you the Magnetic compass bearing to the sun from your vessel on that particular compass heading @ that time.
Then you must calculate the sun's azimuth at those same times in your neck of the woods to ascertain the actual bearings to the sun (or use an app as he did on the video). Convert those true bearings to magnetic as he has done in the video and you have the bearings that you should have initially worked out after reading the reciprocal from the sun card. Any difference between the two is your compass error... Which should be corrected if >5 degrees on any heading (by law on a commercial vessel, recommended on a recreational vessel).
I much prefer the method of sighting straight over the compass bowl at a distant or transit bearing, though it takes practice to get accurate readings on small compasses this way and involves some contorting of the body, as some of you have said. We do encounter more 'blind spots' with this method but overall it involves far less messing about and eliminates the possibility of miscalculation/misunderstanding on the part of the adjuster, and the helmsman need not be exactly on the right heading as he must be with any other method. Misalignment of the Lubber Line has no effect on bearings taken this way, either.
Once one is skilled at it, there's no better way to swing a compass.
I think the video was well produced and easy to follow. The shadow pin certainly has its place, especially when out of sight of land and when it can be placed in the centre of the magnetic compass card on a full sized binnacle on the Monkey Island.
Chris Felan
Compass Adjuster
Thanks.
... excellent, thanks :)
Wait, what?
Nice video. but this is not about compass calibration.
the earth rotates at 360/24 = 15 degrees per hour.how long did your measurements take BECAUSE THE SUN IS MOVING RELATIVE TO TRUE NORTH.......HM..
Take note of the tabulation in the video starting at about 23 minutes, that the total elapsed time for the calibration took about 17 minutes, the bearing to the sun changed by about 5 degrees, and that we recorded the exact time of each observation for use in calculating an accurate bearing to the sun for each observation... MDS
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I am getting sound?
thank you