[TEC] Real navigation Tutorials

[Sean C]

Originally Posted by MrArt

If my time zone is GMT +1 then I must use the Nautical Almanac with a GMT -1 time, and if the time zone is GMT -5
then I have to use GMT +5 time

I'm not sure, but this may be due to the fact that there are two different conventions for naming nautical time zones.


For example: let's say you're at 60° west longitude. Some sources would label this as "GMT -4", because the time there is 4 hours before the time at Greenwich. However, other sources would label it as "GMT +4", because you have to add 4 hours to get to GMT. It's the same thing, just two different ways of looking at it.


Personally, the vast majority of examples I have seen list west longitudes as negative and east as positive. But, I have seen it the other way around occasionally. IIRC, the latter is more popular in European countries and the former in the U.S.


There was a discussion about this very topic on NavList some time ago. I'll try and see if I can find it ...


[EDIT] Here it is: Time Zone Conventions.