Lunitidal Interval Question
Discussion
Science Question - my new watch has arrived and it's ace. However, I have a question for any clever people out there...
It has a tide/lunar phase chart in it. This is good. You have to know the following:
1) Longitude of your chosen beach.
2) Luntidal Interval at your chosen beach.
2) Is easy enough to work out in theory. You need to compare a local tide chart with a local moon chart and you will discover that there is usually a difference between *actual* high tide and the time when the moon is at it's highest. This period is called the lunitidal interval. Generally, *actual* high tide is somewhat after the moon being at it's highest.
Now, for reasons unknown to me, the lunitidal interval on the West Coast of Scotland is actually negative, as in, the *actual* high tide is before the moon reaches it's highest point.
The watch asks you for the lunitidal interval in positive values only, up to 24 hours and minutes.
My question then, is how do I present a negative value for this in positives? Simply subtracting the negative value from 24 seems too easy (-3 hrs for example would be +21 hrs) but it sort of seems logical as well. A quick Google threw up some science nonsense about subtracting things from 12.25 but that scared me so I put it to you...
Mods, this isn't really a watch question despite being to do with a watches feature so not sure where best to put it. I thought here might get the most attention...
It has a tide/lunar phase chart in it. This is good. You have to know the following:
1) Longitude of your chosen beach.
2) Luntidal Interval at your chosen beach.
2) Is easy enough to work out in theory. You need to compare a local tide chart with a local moon chart and you will discover that there is usually a difference between *actual* high tide and the time when the moon is at it's highest. This period is called the lunitidal interval. Generally, *actual* high tide is somewhat after the moon being at it's highest.
Now, for reasons unknown to me, the lunitidal interval on the West Coast of Scotland is actually negative, as in, the *actual* high tide is before the moon reaches it's highest point.
The watch asks you for the lunitidal interval in positive values only, up to 24 hours and minutes.
My question then, is how do I present a negative value for this in positives? Simply subtracting the negative value from 24 seems too easy (-3 hrs for example would be +21 hrs) but it sort of seems logical as well. A quick Google threw up some science nonsense about subtracting things from 12.25 but that scared me so I put it to you...
Mods, this isn't really a watch question despite being to do with a watches feature so not sure where best to put it. I thought here might get the most attention...
It's a G-Shock Gulfman. It just arrived this morning so I'v been playing with it this afternoon. I'm not convinced it's especially accurate for this sort of thing but should give a broad enough indication of whether tide is on the turn or not etc.
Very impressed with the sturdiness thus far.
Very impressed with the sturdiness thus far.
Sounds stupid but are you not sure that it's a positive value, just very high...
as in, meridian to NEXT high tide regardless of when that is, not NEAREST high tide?
Semi diurnal tides in the UK innit? 2 highs and lows a day so it's 12 hours you're interested in.
Any use?
http://www.pol.ac.uk/ntslf/sharing_knowledge.php
as in, meridian to NEXT high tide regardless of when that is, not NEAREST high tide?
Semi diurnal tides in the UK innit? 2 highs and lows a day so it's 12 hours you're interested in.
Any use?
http://www.pol.ac.uk/ntslf/sharing_knowledge.php
Edited by DrTre on Thursday 13th August 16:35
DrTre said:
Sounds stupid but are you not sure that it's a positive value, just very high...
as in, meridian to NEXT high tide regardless of when that is, not NEAREST high tide?
Semi diurnal tides in the UK innit?
Ok, I think I see what you mean.as in, meridian to NEXT high tide regardless of when that is, not NEAREST high tide?
Semi diurnal tides in the UK innit?
Edited by DrTre on Thursday 13th August 16:32
As it happens, I've just done the calculations again (for Machrihanish) and it seems absolutely fine.
Checked the watch against the tide charts and all seems well.
But what was throwing up the question was that I read this:
http://forums.watchuseek.com/showthread.php?p=2159...
Which seems to contradict my findings. Is he just mental and wrong??
Think there's some confusion over the 12 vs 24 hours. There are two highs and lows per day in most of the world because wherever the moon is in the heavens, it pulls the tide toward it and there's a bulge ...however, 180 degrees around the globe there is also a bulge (tide)...
Essentially, forget about the value 24 for most of the earth.
Essentially, forget about the value 24 for most of the earth.
DrTre said:
Think there's some confusion over the 12 vs 24 hours. There are two highs and lows per day in most of the world because wherever the moon is in the heavens, it pulls the tide toward it and there's a bulge ...however, 180 degrees around the globe there is also a bulge (tide)...
Essentially, forget about the value 24 for most of the earth.
For sure but why would the watch provide a theoretical 24 hr value? Is it so that 'negative' values can be covered in the 13-24hr bracket or am I windmilling desperately? Essentially, forget about the value 24 for most of the earth.
Gylen said:
For sure but why would the watch provide a theoretical 24 hr value? Is it so that 'negative' values can be covered in the 13-24hr bracket or am I windmilling desperately?
You're on your own bud, I've confused myself... Having said that, there are places with only one tide a day so they can presumably have an LT up to 24hrs?
(am not understanding the NOAA site about adding 12.42 to the negative value..)
Edited by DrTre on Thursday 13th August 17:05
DrTre said:
Gylen said:
For sure but why would the watch provide a theoretical 24 hr value? Is it so that 'negative' values can be covered in the 13-24hr bracket or am I windmilling desperately?
You're on your own bud, I've confused myself... Having said that, there are places with only one tide a day so they can presumably have an LT up to 24hrs?
Stupid Science! As an aside, I can't even tell what branch of science this question comes under - who would know about this stuff??
james_tigerwoods said:
What does this watch look like - Have you got a link to it. And, dare I ask, how expensive was it?
And. Why?
It looks like this:And. Why?
It cost about £60
and the why is answered by the fact that I surf and wakeboard and consequently seem to break watches quite quickly. I'm informed that these things are nigh on unbreakable so it seemed like a good shout. The tidal thing's a novelty to me really but would be nice to have it working correctly.
As to why I need to wear a watch whilst doing these things, I don't really know. I've just got a thing about it. I could argue that it helps me keep track of water time whilst surfing in Winter so I don't get too cold or that I use it to time tow-time behind the wakeboard boat but that bothers me less than not having a watch on. Can't explain it really
ETA -
at mussel picking. That's the actual answer.Edited by Gylen on Thursday 13th August 17:19
DrTre said:
f
k. Me. I just googled negative and lunitidal and the first result is this thread. How fast does google index? (If that's the right term?)
Fast indeed! Shame it's been moved here though as it's nothing to do with watches whatsoever and more about oceanography as you say. Oh well.k. Me. I just googled negative and lunitidal and the first result is this thread. How fast does google index? (If that's the right term?)Gassing Station | Watches | Top of Page | What's New | My Stuff