View Full Version : Tide clocks and watches

10-11-2005, 08:56 AM
How do they work? given that the tide moves around, moves forward with the moon, backward if you're standing on your head. I can see how a computer chip might do it, close or not so close, depending on the chip. But they've been around a long time. What am I missing?

Andrew Craig-Bennett
10-11-2005, 09:21 AM
They'be been around almost as long as the long case clock, which is either from 1659 or from 1672, depending on whether you count from the Mark One short pendulum job shown by Ahasuerus Fromanteel to Oliver Cromwell in 1659, or the fully fledged standard item, with calendar, metre pendulum and seconds hand, that London clockmakers were turning out by 1672.

London was the Silicon Valley of timekeeping in those years. Before 1659, if your clock was good to within 1/4 of an hour a day, you were doing well. By 1672 it was a minute a week.

The whole world changed. You can date the Industrial Revolution from that point.

The tide phase indicator is just the same as the moon phase indicator that many long case clocks are equipped with (to show which nights of the month you could go out on, since people depended on moonlight for this). It is simply a calendar wheel which rotates once every 28 days. The clocks are all set to the time of high water at one specific port (usually the town they were made in!) but the watches can be adjusted by rotating the motion work.

(As you will gather, I am an old clock enthusiast...)

here's a nice one for Newcastle, from the 1780's, or thereabouts (http://www.allansmithantiqueclocks.co.uk/detailpages/lcmah249.htm)

[ 10-19-2005, 07:04 AM: Message edited by: Andrew Craig-Bennett ]

10-11-2005, 09:22 AM

Tide clocks only approximate tidal variations, and only in a particular place. You set the 'clock' given local info and it takes over. The background showing high and low tides rotates based on the average Lunar cycle. You can get semi-diurnal and diurnal types.

They don't work very well in the Pacific, given mixed tides there, etc.

Bruce Hooke
10-11-2005, 01:10 PM
What you are "missing" is that in places with "normal" tides the interval between high and low tide stays ROUGHLY the same so your basic tide clock is built to reflect that interval. The other half of this equation is that people who buy traditional tide clocks presumably don't care that the clock may be off by as much as (I'd guess) 30 minutes on any given day. Realistically, most people just want to know that there is a high tide around mid-afternoon, rather than that there is supposed to be a high tide at 2:34 PM. Of course even an exact prediction is an approximation in the end because factors like strong onshore winds can have a significant impact on the timing on a given day.

Tide clocks are clearly going to work better in some places than others. Here in Providence we get some wierd interactions between two tidal rivers that branch of from Providence Harbor so the interval between high and low tide varies a bit depending (I'd guess) on how high or low the tides are. I'd expect that in a place with a less complex seabottom that there would be less variation so a tide clock would work better.

10-11-2005, 03:57 PM
Thanks gents.

Sailing a trailerable boat around here the state of tide is controlling. Many of the ramps are only usable at other than low, some are all tides. And, if you are on the river, or need to passage a gut, the ebb and flow timing kicks in. It would be nice to have a clock/watch even if it needed resetting once in awhile and only gave approximations. The internet tells me about various places to the minute here at the desk, but it would be good to have in on your wrist.

Just learning. Tides are a bit of a mystery still. Joe D. pointed out that they don't just come and go, there are stages, times during the middle flood or ebb when the water is moving faster or slower. Add in spring and neep tides and you've got a good study on your hands. All tied to the moon. Very interesting stuff!

Bruce Hooke
10-11-2005, 05:07 PM

I know there are plenty of situations when a more exact prediction does matter. I've certainly encountered some and you gave some more good examples. BUT, I stand by my statement that a lot of the time, for most people, an exact number is not that important, otherwise I don't think tide clocks would be as popular as they are...

Bruce Hooke
10-11-2005, 05:12 PM

A much cheaper and more accurate solution than a watch or clock is to stop by your local hardware store (or bank or whoever does it in your town) in the winter or early spring and pick up a paper tide chart/calendar. This will usually also give you the height of the tide, which is often useful information. At the least, seeing that the tides are running higher and lower than usual (spring tides) will tip you off to expect stronger than usual currents.

- Bruce

10-11-2005, 05:27 PM
How does the tide (or "celestial") function work on a GPS unit? Is it just another brand of the software like Donn runs on his machine, or do the positioning satellites actually track tides as well as other information?

I've found it to be a lot more accurate than any of the published tables. Particularly this past summer, when the tables were frequently off by as much as an hour.

10-11-2005, 05:55 PM
Ishmael, if there's a USCG station near you, ask the NCOIC when they're doing small boat crewmember training or, sometimes, station watch training.

When I was in CG Reserves, I'd have friends or relatives stop by, or phone, and ask for the exact tide changes in areas not too far away. The crew had to learn how to use the tide charts for our area and figure the tidal flow accurately. Once they did, they used to enjoy giving the info out to the public and were always up on the tides. It also became a good PR tool as they would sometimes teach it to other groups.

You'd be suprised how much, depending on the station, those guys enjoy having people come by and ask for little things like that.

If you make a friend at the CG Station, you've got a good friend.

Mike Field
10-19-2005, 03:51 AM
And an earlier thread (http://www.woodenboat-ubb.com/cgi-bin/UBB/ultimatebb.cgi?ubb=get_topic&f=4&t=001280&p=) on this topic.

Kim Whitmyre
10-19-2005, 10:41 AM
I use a nice spiral-bound book from Tidelog. Here's a sample page from their website:


www.tidelog.com (http://www.tidelog.com)

I pick 'em up at Waste Marine.

10-19-2005, 10:53 AM
TIde Tool - a freeware program for Palm (tides and currents) has several locations on the Penobscot river along with hundreds of other tide and current stations on both coasts. It's a good one. Available here (http://en.pdassi.com/product.php?pf=palmos&prod_id=1063)

[ 10-19-2005, 11:55 AM: Message edited by: Canoeyawl ]

Gary Piantedosi
10-20-2005, 11:05 AM
I wear an inexpensive Casio watch ($50?) called 'Fish en Time'. I have no idea how the chip algorithm is set up - you have to load in your long/lat and delta from Greenwich mean time. It will display different info if I load it for Cape Ann vs Provincetown. It constantly displays the tide progress on a bar graph. Press a button and you get a read out of the hi/low times - also sunrise/sunset - moon phase. I may have an older model - I cannot find my exact model on-line - but the models listed seem to have the same features.