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Old 12-07-2016, 16:03   #1
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Question about Deviation and paper charts and logs

I have a question about Deviation and the course steered, and what's logged and charted. This should be an easy question for you paper chart gurus so here goes. Here's my scenario.


The course I want to do is 090M. My Deviation card says I have 5W deviation at 090M.


5W at 090M effectively means to travel on a course of 090M, I need to correct 5E, so the course I give the helmsman is 085M??? Is that right?


So should the course logged be 085M? Or 090M? Do I include a comment like I'd do with leeway?

Likewise what goes on the chart? 085M? O90M? or something else?

If its 085M for the log and/or the chart, how do I show the correction?

TIA
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Old 12-07-2016, 16:12   #2
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Re: Question about Deviation and paper charts and logs

NO TVMDC west is best east is least.. Add 5W to you 090M to get compass

True + Variation = Magnetic Magnetic + Deviation = Compass Going in that direction west is best + and east is least -

Going the other way the signs are reversed.
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Old 12-07-2016, 16:30   #3
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Re: Question about Deviation and paper charts and logs

Bletso,

You're right, forgot about "Timid Virgins". Assume 090M + 5W deviation = 095M is course steered by helmsman. So I assume 095M gets logged as course steered. Correct? But what course get's charted? 090M or 095C?

TIA
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Old 12-07-2016, 16:43   #4
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Re: Question about Deviation and paper charts and logs

I would write on the chart --

103*True
Var 13*E
090*Mag
Dev 5*W
095*Comp

That is what I would write....

I have assumed the local variation for the purpose of completeness.
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Old 12-07-2016, 16:54   #5
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Re: Question about Deviation and paper charts and logs

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Originally Posted by jimp1234 View Post
Bletso,

You're right, forgot about "Timid Virgins". Assume 090M + 5W deviation = 095M is course steered by helmsman. So I assume 095M gets logged as course steered. Correct? But what course get's charted? 090M or 095C?

TIA
I would write 90M or xxT along the line I drew on the chart.
Same with the log.

I might also include 95C in the log. If I did I would reproduce the deviation card in the log the first or last day of every month or every other month including the epoc(date the card was produced) This makes the info easy to find if the card is lost, provides legal support that you had the card and were using it and reminds you of how old the card is and maybe you should redo the card now that it is 4yr old.
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Old 13-07-2016, 03:36   #6
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Re: Question about Deviation and paper charts and logs

Personally I only chart true Course. True remains true but on small scale charts you may have variation changes across the chart. Let the ship's log note your course steered.
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Old 13-07-2016, 04:01   #7
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Question about Deviation and paper charts and logs

You can draw and log the course as "T" for True or "PSC" Per Ships Compass. I would log PSC as this would log any TVMDCAw errors.

Generally PSC is the KISS way. Based on experience when things go pear-shaped, you want it simple. Also since the crew may not be experienced paper chart people. If you are asleep and they need to look at the chart to confirm heading using PSC will ensure they steer the right course..... Well at least decrease the odds of a f-up.

The truly OCD (CDO) can write T above the course line and PSC below.
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Old 13-07-2016, 04:32   #8
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Re: Question about Deviation and paper charts and logs

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Originally Posted by bletso View Post
NO TVMDC west is best east is least.. Add 5W to you 090M to get compass

True + Variation = Magnetic Magnetic + Deviation = Compass Going in that direction west is best + and east is least -

Going the other way the signs are reversed.

When teaching coastal navigation, many students get confused over whether to add or subtract deviation/variation. The "...west is best, east is least" phrase doesn't seem to do it for most. So, I came up with my own variation on this mnemonic which has worked well and its humorous too!

"Many students miss questions because of slight errors in converting between True/Magnetic/Compass. The old mnemonic for bearing/heading conversions is True Virgins Make Dull Company (TVMDC). It falls a bit short because it does not really help remind you of how to handle East-West variation/deviation. I have my own extended version of the mnemonic: "True Virgins Make Dull Company add Whisky, subtract Ethics". A nice feature of this one is that it flows logically from True to Magnetic to Compass and in the opposite direction too. For example, if you are converting from True to Compass then you can think of this as "corrupting" the bearing/heading/course. Therefore to corrupt you add Whisky (West) and subtract Ethics (East)....the result is more "interesting" company and a correct conversion. If you are "purifying" (going from Compass to True for example) then you do the opposite: add Ethics, subtract Whisky."
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Old 13-07-2016, 04:38   #9
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Re: Question about Deviation and paper charts and logs

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Personally I only chart true Course. True remains true but on small scale charts you may have variation changes across the chart. Let the ship's log note your course steered.
I prefer to plot course lines in True also. If you work professionally at all then you will likely be razzed a bit if you don't. It is also the least common denominator so to speak and you can easily convert to magnetic or PSC as needed.

An advantage of working in True is that you don't have to walk a nav tool, like parallel rules, all the way over to a compass rose, you can just go to the nearest lat/lon line to get the angle. Very handy.
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Old 13-07-2016, 09:26   #10
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Re: Question about Deviation and paper charts and logs

Dear Belize Sailor -

i have been walking around the boat chanting "Add whisky, subtract ethics" for 10 minutes. My partner thinks I've lost it. Truth is I think I will never be lost again.

"Add whiskey, subtract ethics, add whiskey...."

Thanks!
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Old 13-07-2016, 10:26   #11
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Re: Question about Deviation and paper charts and logs

Choices are always good!

Yes true is the standard. And when motoring on a vessel with watch officers that are skilled enough to run the vessel steered by a helmsman who could plot a course---- you make100% sense.

But we are talking cruisers here. As a sailor who either single-hands or sails with non-sailors or "click" navigators, I will continue to plot PSC. I don't want to be babbling mnemonics in the middle of the night trying to figure out where I am or going. Or why I am so far off course.

Finally, if incapacitated-- ponder trying to explain back course headings to a less skilled crew. Assuming a fiberglass boat with nominal deviation, PSC is easily flipped to a back course-- add or subtract 180 until you get a result less than 359.

Different strokes for different folks---- cheers.


Sent from my iPhone- please forgive autocorrect errors.
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Old 13-07-2016, 11:01   #12
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Re: Question about Deviation and paper charts and logs

I am old school. Learned TWA (anyone remember Trans World Airlines?). True, West, Add. Going from magnetic to compass is the same direction as starting from True. I think it is ok to plot magnetic, but wouldn't plot compass as it is boat specific and may even change if add equipment to that boat.
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Old 13-07-2016, 14:19   #13
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Re: Question about Deviation and paper charts and logs

Quote:
Originally Posted by redhead View Post
Dear Belize Sailor -

i have been walking around the boat chanting "Add whisky, subtract ethics" for 10 minutes. My partner thinks I've lost it. Truth is I think I will never be lost again.

"Add whiskey, subtract ethics, add whiskey...."

Thanks!
Glad you enjoyed it!
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Old 13-07-2016, 15:19   #14
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Re: Question about Deviation and paper charts and logs

My take:

As a practical matter, if you are navigating on a chart and steering by magnetic compass, and if you are using logs...

...you should be using both a navigation log, showing courses steered and speed and depth and other navigation parameters, including fixes taken (or recorded at intervals for continuous fix information), and a compass log which should show corrections.

The progress toward a the destination or waypoint will be made by steering the compass course. Thus the order to the helm is to steer the corrected magnetic course, and the ordered course is the course that should be logged.

The plot of progress/DR plot will be the same whether plotted using true or corrected magnetic heading. Labeling should be a matter of local policy, and can be either true or magnetic (but be consistent).
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Old 13-07-2016, 15:46   #15
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Re: Question about Deviation and paper charts and logs

I'm still a great believer in 'showing your working'.
If you simply write xxx*C on the chart no one will pick up the fact that you have screwed up your workings... as the OP did up at #1.
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