Length of day at high latitudes?

Ladybirdgaffcutter

Ladybirdgaffcutter

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This is a quote from Eric Newby:

"...on 24 March, 1939, at 50 degrees South, 170 degrees West, she ran 296 miles in 23 1/2 hours with the wind WSW (a day noon to noon in these high latitudes is only about 23 1/2 hours)..."

(She being Ericson's Moshulu of course.)

Surely a day is the same at all latitudes, and Newby has absorbed some focsle old wives' tale here?
Or am I missing something?
 
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Quick calc say that if he was sailing East at 7kts at 50S he would have sailed 1/48 of a circumference and his day would therefore be a half hour shorter, by local time. Recovering from having something removed from an eye means that I may have missed something...
 
anoccasionalyachtsman said:
Quick calc say that if he was sailing East at 7kts at 50S he would have sailed 1/48 of a circumference and his day would therefore be a half hour shorter, by local time. Recovering from having something removed from an eye means that I may have missed something...
Click to expand...

Indeed. A day for a person on land will still be exactly 24 hours but a day as perceived by someone on a moving object will be a variable feast.

I suppose that if you were standing close to the rotational point of the earth and you ran extremely quickly around that point, ignoring precession, you could make a day last almost 48 hours. ;)

Richard
 
anoccasionalyachtsman said:
Quick calc say that if he was sailing East at 7kts at 50S he would have sailed 1/48 of a circumference and his day would therefore be a half hour shorter, by local time. Recovering from having something removed from an eye means that I may have missed something...
Click to expand...

I dont get that result...

Earth radius (equatorial) = 3963 miles
Radius at 50 North = Re * cos (50) = 2547 miles
Circumference at 50 North = pi * 2 * 2547 = 16005 miles.

So 296 miles is more like 1/81 of the way round.

No?
 
'Noon' has a different meaning to sailors... or at least it did in pre GPS days.

Some tramp steamers as late as WW2 would reset their clocks at local apparent noon each day, the result being days of all sorts of odd lengths.
The norm however was to put the clocks forward by half an hour or a full hour - depending on the ship's speed - at midnight so that 'noon'/mer. pass. the following day would fall close to 1200 clock time.
 
Lon nan Gruagach said:
I dont get that result...

Earth radius (equatorial) = 3963 miles
Radius at 50 North = Re * cos (50) = 2547 miles
Circumference at 50 North = pi * 2 * 2547 = 16005 miles.

So 296 miles is more like 1/81 of the way round.

No?
Click to expand...

The earth is not very spherical.
But roughly, if it was a sphere,
pole to equator = 10,000km. NM=1852m
Circumference= 21600 ish NM
circle at 50 degrees (cos= 0.642) =13883
13883/296=46.9
 
From Opencpn - 294Nm W at 50S ~ just under 8deg ~ half an hour?

yQKMcS2.png



Or at the equater > 7.5 deg (30 minutes) x 60 = 450Nm, at 50N > 450 x cos(50) = 289Nm.
 
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Lon nan Gruagach said:
I dont get that result...

Earth radius (equatorial) = 3963 miles
Radius at 50 North = Re * cos (50) = 2547 miles
Circumference at 50 North = pi * 2 * 2547 = 16005 miles.

So 296 miles is more like 1/81 of the way round.

No?
Click to expand...

Quite right. I forgot to double the 4,000 Cos 50. (Without a bracket...).

As for the inaccuracy of the rest of my wrong answer - I should have said about 7kts 'cos I did it in me head.
 
More than a few red herrings being chucked into the mix here.... oblate spheriods and sidereal days included.

Square rigger running her easting down in 45*S at 15 knots..... 360 miles a ( 24h) day.

If she was at the equator that would see her covering 6* of longitude a day

At 45*S that would be 6*/.7 = 8.5*.

So they would be advancing the clocks 30 minutes every night with a 1 hour advance about once a week.
 
Frank Holden said:
'Noon' has a different meaning to sailors... or at least it did in pre GPS days.

Some tramp steamers as late as WW2 would reset their clocks at local apparent noon each day, the result being days of all sorts of odd lengths.
The norm however was to put the clocks forward by half an hour or a full hour - depending on the ship's speed - at midnight so that 'noon'/mer. pass. the following day would fall close to 1200 clock time.
Click to expand...

I thought ships advanced/retarded their ‘ships clocks for local time’ at the dogs? Or is that just an RN thing?
 
john_morris_uk said:
I thought ships advanced/retarded their ‘ships clocks for local time’ at the dogs? Or is that just an RN thing?
Click to expand...

Mustafa Bin a navy thing...
Typically in MN clocks would be changed at midnight but the time lost (ie shorter watch ) would be shared between the 8-12, 12-4 and the 4-8.. If westbound the C/O would let the 2/0 and 3/0 suck up all the extra time on watch.. Varied a bit between companies and ships but MN doesn't have 'dogs'....

Same same the date line.... gain a day? Oh look its a week day...! Lose a day?.... ooops there goes our day of rest....
 
>Surely a day is the same at all latitudes,

Our skydiving team was jumping a Hercules in Sweden and it didn't get dark until midnight, in the Caribbean it is 12 hours of darkness and 12 of light.
 
KellysEye said:
>Surely a day is the same at all latitudes,

Our skydiving team was jumping a Hercules in Sweden and it didn't get dark until midnight, in the Caribbean it is 12 hours of darkness and 12 of light.
Click to expand...

Yes but.....

Hours of daylight vary by latitude and season...

A navigator's day runs from 1200 to 1200 ( ship's time ) ... whether that be a 23 hour day or a 25 hour day or something in-between...
 
Frank Holden said:
Yes but.....

Hours of daylight vary by latitude and season...

A navigator's day runs from 1200 to 1200 ( ship's time ) ... whether that be a 23 hour day or a 25 hour day or something in-between...
Click to expand...

Did you ever run noon to noon UT? For navigation purposes rather than crew watchkeeping in Local?
 
capnsensible said:
Did you ever run noon to noon UT? For navigation purposes rather than crew watchkeeping in Local?
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Nope.... day was always to 1200 ship's time..... however ...

On the Union-Castle mail ships we would leave Southampton on GMT ( or BST ) and not touch the clocks until 2 ( or 1 ) nights before Capetown despite going well west around the bulgy bit of Africa.... so as not to confuse the passos...

For much of the trip mer alts were something the 2/0 did in the middle of the afternoon to keep himself amused .... 'day's run' was calculated using 'sun-run-sun' and two Marq St Hilaires.....

¿Qué 'UT'? ... sounds positively Bonapartiste....
 
dunedin said:
Wow 50 degrees is high latitude. Think only Lizard Point in Britain is the only place in lower latitudes then.
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Yes, that's what I was thinking. Sailing on the West Coast, I never really thought of myself being a rufty-tuffty High Latitude sailor.:D
 
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