Posted by Andrew Craig-Bennett on March 10, 2007 at 19:25:12 from 195.93.21.42 user ACB.
In Reply to: High water full and change (was Journey back from Secret Water) posted by Jock on March 08, 2007 at 18:56:48:
The term "High Water Full and Change" ("HWFC") is not really ancient - if anyone still has one of the earlier copies, say, from 30 years ago, of Jack Coote's "East Coast Rivers", they will find it included in the data for each place described.
I had no idea that I was using an obscure old term - AR and Captain Flint, to say nothing of Commander Walker, would certainly have known and used it. I wasn't planning to show off.
The ancient version of the term is "The Establishment of the Port", and you will find this in all old Pilot Books.
Now, what is it and why?
I'm afraid it's dead simple:
It just means the time of High Water at a given place when the Moon is either Full or Changing (i.e., when there is a full Moon or no Moon).
This time varies from place to place, but is constant for each place.
As Jock correctly points out, in the North Sea, Spring tides occur a couple of days after High Water Full and Change, at each place.
So, why do we need to know "The Establishment of the Port" ("HWFC")?
Well, we might not have Tide Tables for the place with us. Indeed, years ago, we certainly would not have had any. But if we know the time of HWFC we can work out when the times of Spring and Neap tides will be if we know the phase of the Moon for the date when we plan to visit the place that we are interested in.
In replying to Paul, I used the time of HWFC Walton, which I happened to remember from an old copy of Jack Coote's "East Coast Rivers" to calculate when he might best plan a visit to Secret Water which involved launching a dinghy.
Another application of the same principle occurs in clock making. You may sometimes see a long case clock (another enthusiasm of mine) which tells you, in addition to the time, the time of High Water at a port (usually the port where the clock was made - I have seen them for Ipswich and Bristol). Modern tidal prediction watches use the same information but allow you to select from a range of places.
You have probably noticed that Spring and Neap tides occur at the same times of day for a given place - this is why.
Before Tide Tables were published, which is not that long ago, people relied on knowing the Establishment of the Port to calculate their tides and thus to know if they could get their vessel over a bar, up a river, etc. Of course, in those days, people were much more at home with the phases of the moon than we are now, because there was no street lighting, so dinner parties and dances were always held near to the time of Full Moon.