But if not...
Join Date: Sep 2011
Location: Annapolis MD
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Re: Ram mic mounting location??
fyi - I have a write-up and table I use to swing our compass occasionally. My personal preference is to use the sun rather than a second compass - I always have a nagging bit of doubt about 2 compasses, 2 deviation tables, etc.
Anyway, this procedure uses simple sun shadows and only takes a few minutes.
I'll insert the text here since I can't seem to upload a Word file. No promises about how the formatting will turn out. If you'd like the Word file, just let me know where to send it (or point me in the right direction for uploading.)
Build a Sun compass
❑ Glue a compass rose cut from a chart or SAPS sheet to a block of wood
❑ Drill a hole through the center of the compass rose into the block of wood to support a poultry skewer, long thin pin, brad or similar.
Swing the compass
- all courses should be completed within 5 minutes to limit the effects of the changing location of the sun.
- longest shadows will be early or late in the day
❑ Site the compass rose for the least interference from shadows and where it can be read with ease. Align the 0 (North) of the compass rose with the bow (not necessary, but simpler)
❑ Steer the compass course indicated. When the course is steady, note the bearing of the shadow on the compass rose. Repeat for each compass course in the table.
❑ Record all solar shadow bearings in the deviation table.
❑ Add course (col A) + Solar Shadow Bearing (col B). If greater than 360, subtract 360 from the sum. Record Sum in column C.
❑ Calculate average Sum (Total Column C divided by number of observations recorded, not total # of rows). Record in each row of Column D.
❑ Calculate Deviation for each course. Deviation = average sum – sum. If average sum > sum, deviation is east. Record in Column E.
❑ If possible, complete 2 or 3 runs and average the deviations obtained. If some headings were obscured by shadows, steer headings as close as possible.
❑ Graph the resulting deviation. If the majority of deviations fall either east or west, consider turning the compass in the binnacle slightly to compensate.
Deviation Table (example)
A B C D E
Comp Course Solar Shadow Sum (A+B) Avg Sum Dev
000 290 290 292 2E
030 260 290 292 2E
060 233 293 292 1W
090 192 292 292 0
120 173 293 292 1W
150 145 295 292 3W
180 114 294 292 2W
210 085 295 292 3W
240 052 292 292 0
270 022 292 292 0
300 351 291 292 1E
330 320 290 292 2E