OK Navigators, what are these for?

[Cpt Pat]

The bottom number is assigned heading. The top number can't be variation (offset between true and magnetic heading) because it only accommodates one digit positive or negative. It must be compass deviation (compass heading error). In the photo, it would be interpreted as: "assigned heading 264 degrees, steer 262 degrees indicated." The deviation would be looked up in the compass deviation table complied the last time the boat was "swung."


The assigned magnetic heading would be calculated from the charted heading degrees true. Then, the local variation would be added or subtracted. East variation: subtract to get magnetic. West variation: add to get magnetic heading. "East is least and west is best."

[CHRIS V CLEMENT]

If my memory of navigation classes 40 years ago are correct, the anacronym, CAN DEAD MEN VOTE TWICE AT ELECTIONS comes to mind.

If one writes the first letter of each word vertically, we have the following table :
C ......a compass magnetic reading.
D.......the deviation caused by metal around the compass.
M.......the magnetic heading shown on the compass.
V........the variation shown on the chart inner compass rose
T........the true heading shown on a gps or most auto pilots
A........add any easterly variation
E........the easterly variation described above....

I apologize ahead of time if my memory have failed me. I still use paper charts, by I am so close to the Mississippi River that variation typically is not an issue.....and both of my handheld GPS receivers are always close at hand during any travels of any distance....even 5 miles...

[Cadence]

Originally Posted by Cpt Pat

The bottom number is assigned heading. The top number can't be variation (offset between true and magnetic heading) because it only accommodates one digit positive or negative. My first guess is it's compass deviation. In the photo, it would be interpreted as: "assigned heading 264 degrees, steer 262 degrees indicated."

I believe you are probably correct. Something left for the helmsman by the navigator.

[El Pinguino]

'Queen Mary' would never have had a helmsman steering a compass course using the compass in the binnacle... being fitted as she was with a Sperry gyro compass... the repeater for the Sperry can be seen on the left of the binnacle... the helmsman would have steered by that.

When entering or leaving port fr'instance and in hand steering course to steer would have been given in 'True' and the helmsman would have been steering with reference to that repeater.

What you see there is the almost identical setup to what I was used to on the British liners I served on.. the most modern - 'Windsor Castle' - being built as recently(? ) as 1959. She still had (magnetic ) steering compass in front of the wheel, (magnetic ) standard compass on the monkey island/flying bridge, and an offset gyro repeater next to the steering compass and the helm. No periscope to the standard compass... just a speaking tube..

Minor differences... the chalk board was off to the side and just the 'course to steer' was in front of the helm.

The +/- bit is unusual... but then it was Cunard......

[Maka]

Those are the Hymn numbers to be sung during the service. They are posted there so you can look them up before hand and be ready to sing when the time comes.

[Don C L]

I did not know about the gyro, that makes a lot of sense. One thing I thought may have been involved, which probably was not now that I see the responses, is that during the war the ship made regular turns in a zig-zag track across the Atlantic. Perhaps accounting for deviation and variation changes was my original idea, but I see now not likely. I thought Snowpetrel’s idea of set and drift was interesting... Pinguino? Growler? That possible? Btw, I wonder if someone left the heading of 264 in there for some historically important reason?

[El Pinguino]

I just laid of a very rough rhumb line from Southampton to New York and that was 258*... maybe that is involved.

Nothing to do with with set and drift would have been on those boards... I think it is what it is...

Off to the right of the binnacle you would have seen the actual Sperry Autopilot http://img04.deviantart.net/d12f/i/2...ic-d74azgu.jpg
with a bloody great gear lever on its left to engage/disengage the autopilot and a wheel to adjust the course with... horrible machine ... if somebody brushed the wheel when walking past the course changed.... not good. Still being put on new ships in the 60's...

Sperry Mk 14's History of Sperry Marine | Sperry Marine driving all this date from the early 1930s and the actual gyro would have either been in a corner of the wheelhouse , or deep in the bowels of the ship...

Of all the things I could have from an old ship... I would pass by the sextants, binnacles, and chronometers and get myself a working Mk 14...

Stick a naked one in front the living room window and I would never again have problems with small boys or stray dogs on my front lawn... closest thing you will ever find to a real live Dalek...

[captlloyd]

Originally Posted by 44'cruisingcat

There's a spot to write variation on the blackboard.

Tide flow and direction?

You are right about it being on the blackboard but nothing is written on it either. I vote for variation because variation could change due to location and watch or watches. I could be mistaken, I was once in 1952. Never lived it down.

[budm303]

Originally Posted by CHRIS V CLEMENT

If my memory of navigation classes 40 years ago are correct, the anacronym, CAN DEAD MEN VOTE TWICE AT ELECTIONS comes to mind.

If one writes the first letter of each word vertically, we have the following table :
C ......a compass magnetic reading.
D.......the deviation caused by metal around the compass.
M.......the magnetic heading shown on the compass.
V........the variation shown on the chart inner compass rose
T........the true heading shown on a gps or most auto pilots
A........add any easterly variation
E........the easterly variation described above....

I apologize ahead of time if my memory have failed me. I still use paper charts, by I am so close to the Mississippi River that variation typically is not an issue.....and both of my handheld GPS receivers are always close at hand during any travels of any distance....even 5 miles...

Working back (TVMDC--how to find your heading) True Virgins Make Dull Company, taught in '50s classes at Keesler AFB.

[Lodesman]

Originally Posted by El Pinguino

Steered offshore by autopilot.... upper numbers refer to gyro error which is refered to as + or - .... not E or W....

Rarely if ever more gyro error than 2* high or low.

She had gyro and autopilot as built.. Part 16

Why would the helmsman care about gyro error? He would steer the gyro course given, the navigator would worry about the gyro error.

I figure the top number refers to the amount of helm being carried to maintain course; an assessment made by the helmsman, but occasionally asked for by the OOW.

[Cpt Pat]

Originally Posted by Maka

Those are the Hymn numbers to be sung during the service. They are posted there so you can look them up before hand and be ready to sing when the time comes.

If they started singing "Eternal Father Strong to Save" from the bridge, I think I might start uncovering a lifeboat when they got to the: "for those in peril on the sea" part.

[Don C L]

Not sure if it is clear but there is a little arrow between the two number slots on top that, I presume, can spin to point to either the positive or negative number. So I wonder who is placing these numbers and writing on the board? The navigator or the helmsman?

[CSY Man]

. So I wonder who is placing these numbers and writing on the board? The navigator or the helmsman?

Probably the navigator: I have helmed a few Merchant ships for a living and never been asked to write no numbers on no board, my only job was to either steer a course if in open waters, or manipulate the helm as per orders from the navigator, or more often, the harbor pilot when in close quarters.
If the auto pilot was engaged, I was dismissed out to the bridge wing to look for traffic.
In busy harbors we were two OS or AB’s alternating steering the ship 1 hour each while on the 4 on, 8 off watches.

[GrowleyMonster]

Originally Posted by Lodesman

Why would the helmsman care about gyro error? He would steer the gyro course given, the navigator would worry about the gyro error.

I figure the top number refers to the amount of helm being carried to maintain course; an assessment made by the helmsman, but occasionally asked for by the OOW.

That is actually rather logical though not current practice because very little hand steering these days, just when in a narrow channel or other confined waters or docking/undocking. At sea she will be on the Mike except when hand steering for training purposes.

[Snowpetrel]

If she had a gyro I reckon it could well reflect the gyro repeater error. As in steer 264°G for 266°T with a 2° low gyro error. It is quite possible for each repeater to have a slightly different error even on more modern systems. We often had one bridge wing 1/2 high and the other 1/2 low. It was very hard to adjust out at sea, so we just made allowances for it.