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808state 02-05-2004 12:03 PM

Check My Plotting...
Hello all, as a budding cruiser, I am currently studying coastal navitgation at home with the US Sailing book, and plan on taking a nav course this spring. I''m looking for a competent navigator to check my work, with relation to plotting;true to compass, factoring variation and deviation. Here are the #''s...
Compass Rose says... Var7deg30W, (2000), annual increase 10''.
My #''s- 10''x4=40 div by 60minutes =.66. New Var=7.66.
My bearing is 130T+ 7.66V =137.66M - 4E(dev)= 133.66 Compass.
Question: If my #''s are correct, should I steer a compass heading of 133, 134, or try to stay in between, (hard to do on a boat)? Do these small half a degree increments matter? Thank you!

e-27 sailor 02-07-2004 12:04 PM

Check My Plotting...
While it''s important to know how you got to 133.66, compasses are graduated in 5 degree increments. And while large ships with powerful autopilots may be able to hold a heading within 5 degrees, sailboats can''t. Offshore, between large swells and wind gusts/lulls & shifts, I think holding a heading within 20-30 degrees is reasonable. After all, sailing is a fluid environment.

elhanley 02-23-2004 01:34 PM

Check My Plotting...
Whether you are manning the wheel or setting the autopilot, it''s as easy (or difficult) to read between the compass graduations as on them; however, normal steering errors, estimating currents and leeway, etc., will add up to a much larger tolerance than even several degrees. In the middle of the ocean, that is not important. As you approach its jagged edges, however, you need to rely on your GPS, radar, and piloting skills. I won''t give away my age by suggesting celestial navigation as being helpful.

gstraub 02-24-2004 02:57 AM

Check My Plotting...
Well, if I did it right, you''re close. Your Variation is 7 deg 30 min W (I think, you didn''t say 30 min, but I am assuming that is what it is) with an annual increase of 10 min. In 4 years that is 40 min, so your total variation is 7 deg 30 min plus 40 min (you dropped the 30 min from the original year 2000 variation), which is 8 deg 10 min W. So, your magnetic course then becomes 130 deg plus 8deg 10 min which equals 138 deg 10 min or in decimal form 138.17 degrees. Now correct for your deviation as you did and you get a compass course of 134 deg 10 min.

However, as the other replies indicate, you won''t be able to steer that accurately, so you''ll just have to average it out over time. Your actual course will probably wander 5 or more degrees either side.


BigRed56 02-24-2004 02:35 PM

Check My Plotting...
Ahoy me matey, Yes it does matter so get it correct ten times out of ten and keep asking others to check your work iffin ye a troubled wit de doubts what command places on yer head. Compounded over time and distance it''s the equivialent of making Bermuda or Africa. Nows I did me own calculations wit yer numbers and even iffin I ani''t never meet dat Compass Rose wench I tinks ye outten not be asking some silly trim such serious matters... wot in de hell was I saying?? oh yeah I figure wit yer numbers your exact position is just to de port of Cleveland Ohio and I suspect dat neighborhood ain''t wots got you into sailing so''s haul up yer jenny and head due south till de water is warm under yer keel and de rum is a smooth as .... ...... ..... ....., on dat roses .........! AARRGGHH Pirate of Pine Island.

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