Tide Tables - Local time, or what?

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Sitting here in Gibraltar without tide tables (we don't have a need for them most of the time in the Med) I was delighted to find that one can download, free of charge, the entire annual tables for British overseas dependencies such as Gib.

http://www.pol.ac.uk/ntslf/pdf/gib2007_minusone.pdf

However, at the top of the tables it says "Time Zone -0100" and I've forgotten what that means if I ever did know. Reeds always used to make that absolutely unambiguous. So what does "Time Zone -0100" mean when it comes to using the tables? Are the times shown Local Time (i.e. legal time), Summer Time, or UTC/GMT? What do I need to do to convert them into Local Time, which is what we work with on board? BTW, Gibraltar uses the same clock setting as Madrid, Paris, Rome and we are one hour ahead of London.

Many thanks.
 
Would I be correct in saying that -001 would be the time for 1 longatude east of GMT, or 1hr earlier than GMT.
I have a scale for this on the instruction leaflet for my electronic weather station and was reading it only last week, but it is down at the boat and I wont be there for over a week as I am starting the day skipper practical on sun.
 
David,

The Imray Med Almanac shows Gib as Time Zone -0100

at the top of the tide page it says:

"Subtract 1 hour for UT. Summer Time (25.03.2007 to 27.10.2007) add 1 hour"

To compare with what you have, the tides for Saturday 15 September are (direct copy from the almanac - not corrected) :

0457 0.9
1029 0.2
1707 0.9
2251 0.2

(Not wishing to confuse, but I also dont understand the Time Zone -0100 which suggests UT-1, whereas subtracting 1 hour to get UT suggests UT+1, nevertheless, if you do what it says and add 1 hour to get Summer Time you should be fine).

Hope that helps

Richard
 
Just realised my previous post was Bollocks... so deleted it... and try again...

if the table is in -0100 then it shows times one hour later than UTC, eg subtract 1hr from the table to get UTC..... if Gib time is UTC+1, then the time effectively shown is LT, but not allowing for daylight saving... so while DST is in operation, you'll need to add an hour to the shown times to get LT.....
 
Zone time is the local standard time, no allowance being made for summer time or daylight saving.

The figure -0100 tells you that your standard time is 1 hour fast on GMT ie when it 1200 hours GMT your <u>Standard </u> time will be 1300.

Assuming you keep your clocks set to the local times then what it says in the tide table will be in agreement with your clocks. EXCEPT that you will have to add 1 hour to those times during the period in which summertime (or daylight saving) is in operation (Just as you would to uncorrected tide tables for the UK).


Most of the world types faster than me irrespective of their time zone!
 
Richard, and everyone, thanks!

Saturday 15th
Imray______________Pol
0457 0.9____________0453 0.9
1029 0.2 ___________1025 0.13
1707 0.9____________1659 0.9
2251 0.2____________2246 0.13

So they are very close but I wonder where the difference comes from? Were they from a different standard port?

We are saying, then, that the time of first high water on 15th September will be 1125 Local time (or 1129)?

I wonder why they don't just give it in UTC and have done with it?

Many thanks, David
 
[ QUOTE ]
So they are very close but I wonder where the difference comes from? Were they from a different standard port?

We are saying, then, that the time of first high water on 15th September will be 1125 Local time (or 1129)?

I wonder why they don't just give it in UTC and have done with it?

[/ QUOTE ]

Gib is a standard port but they are only predictions so maybe one computer model gives slightly different results to another. or maybe the web site you are using uses fixed time differences from somewhere like Lisbon, or London, or wherever, (a bit like a secondary port), whereas the Almanac uses the actual predictions for Gib) - I'm waffling, what do I know?

1125 is my take on it, (or 1129).

I suppose that they make it so that for part of the year, it is the figure on the table, and for the other part you have to add only 1 hour, just like Reeds for the UK.

e.g. using UT in Sydney would be very confusing, (having said that, I dont remember what they use in Aussie tide tables, so they might use UT <g>).
 
Yes, it might be inconvenient for, say, Sydney but you would always be able to work it out for yourself instead of posting a message on a forum /forums/images/graemlins/wink.gif Anyway, no probs now thanks to YBW and the terrific posters willing to come to the rescue even at midnight! You wouldn't get a service like this if you PAID for it! Thanks again.
 
[ QUOTE ]


Saturday 15th
Imray______________Pol
0457 0.9____________0453 0.9
1029 0.2 ___________1025 0.13
1707 0.9____________1659 0.9
2251 0.2____________2246 0.13

So they are very close but I wonder where the difference comes from? Were they from a different standard port?



[/ QUOTE ]

Maybe Imray use UKHO constants ?
Proudman use their own, and there's often a tiny difference between their's and the Admiralty - insignificant in the real world.

Colin
 
[ QUOTE ]
(Not wishing to confuse, but I also dont understand the Time Zone -0100 which suggests UT-1, whereas subtracting 1 hour to get UT suggests UT+1, nevertheless, if you do what it says and add 1 hour to get Summer Time you should be fine).

[/ QUOTE ]Richard, the trick to remembering this is to just note that the time zone is what you need to do to the shown times to get to UTC.... eg -0100 means take off an hour from the shown times to get to UTC.... and you can then reverse engineer it, by adding an hour to UTC (ignoring DST) to get to LT.....

Useful to get sorted in your head, as then you can do all your nav in UTC and convert final results to LT...
 
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