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Author
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Topic: Watch time vs GMT?
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annabell
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posted February 12, 2003 10:19 PM
I notice that all of starpath course materials use a time system called "watch time" instead of GMT. Is is not better to use GMT directly since we must end up using GMT to do celestial anyway?
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David Burch
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posted February 12, 2003 10:30 PM
We use watch time because we recommend navigating by the watch you wear, and we recommend this becuase if you do so you will always know the rate of the watch you have with you. If you even get stuck in an emergency, your watch is the most important nav aid to have. With it alone you can sail around the world; without known time, it is difficult to DR for a hundred miles.
Futhermore, no matter what time piece we use, we will have to make corrections to it, at least for watch error. So adding a fixed number of hours is no more difficult than making the correction for watch error... ie we do not same time in computations.
Also, it is not very practical in most cases to have your watch set to GMT (unless you have two time zones on it). The watch you wear should read the ships time and we recommend not changing this time zone during a voyage. Hence if I use ZD=+7 for summer time in Seattle, as i leave to sail for HI (zd=+10) then i would leave the watch set to +7 till we arrive. then i know whenever i do a sight, i add 7 hr and make the WE correction.... but most important, if i get stuck some how and have to rely on what i have with me, i have correct time.
From: Starpath, Seattle, WA
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MacRae
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posted March 04, 2003 04:48 PM
Doesn't watch time become a problem when you're communicating with other boats that departed from other time zones?
Thanks,
MM
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vjwilliams
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posted March 08, 2003 02:43 PM
Watch Time is proposed as a time keeping system for navigation and general smallcraft on-board operations. That is, it is your own personal ship's time. As such it is usually not pertinent to outside communications.
When it comes to communicating with other vessels or with shore stations you must decide what is the most appropriate time system and use that. In many cases, using GMT for that purpose might clarify the communications. It all depends on who you are talking to and about what. If at the end of a long passage to Hawaii you care to know if the bars will still be open when you get there, you must start thinking in terms of local Hawaii time for that particular communication.
You will always have to be prepared to make this evaluation, regardless of your local ship's time. It may well be that you want to communicate with a vessel that doesn't even know what GMT is, and certainly many land communications will not find GMT convenient.
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Kornelius Baade
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posted September 18, 2003 12:06 AM
I belive that if we keep on finding new names for the time , everyone will be confused .
I have learnt that the time that you call "watch time " is the same as "local mean time (lmt)" I would belive that we have enough to do , and another name for something there already is plenty names on , is not needed. If everyone started to use a common name for all values ,it would easier for all mariners around the world to understand each other during comunication .
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David Burch
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posted September 18, 2003 01:36 PM
I belive that if we keep on finding new names for the time , everyone will be confused.
== this is completely correct. we should not make up unnecessary names, it is confusing and rarely adds to convenience.
I have learnt that the time that you call "watch time " is the same as "local mean time (lmt)"
== this is not the case. Watch time and Local mean time are * completely different * time concepts. We use WT throughout the course, we do not use LMT as such at all.
== both are defined in the course materials, as discussed above.
I would belive that we have enough to do , and another name for something there already is plenty names on , is not needed. If everyone started to use a common name for all values ,it would easier for all mariners around the world to understand each other during comunication .
== Watch time is not a new term. It is a standard term in navigation. As discussed above, however, you might want to use GMT or ZT for radio communications.
--david
From: Starpath, Seattle, WA
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