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Old 30-09-2011, 07:09   #1
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Time and Tide Clocks

I am quite new in this sailing thing and I really want to know how can a time and tide clock assist in my safe and smooth sailing. I also want to know how to choose the most efficient kind of time and tide clock. I guess I am looking for some kind of criteria to make a better decision.

Appreciate any feedback.

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Old 30-09-2011, 07:34   #2
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Re: Time and Tide Clocks

Where are you sailing? I don't know about a clock. Tides may be significantly altered by weather and might vary greatly just a few miles away from your home base. I rely on tide tables, the rule of twelves (with a pinch of salt), depth sounder and my eyes.
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Old 30-09-2011, 07:59   #3
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Re: Time and Tide Clocks

Greetings and welcome aboard the CF, sailormoon.

Tide clocks only keep an approximation of the average time between high lunar tides based upon 12 hours 25 minutes per revolution.
Since the precise average time between high lunar tides is actually half of a lunar day, or 12 hours 25 minutes 14 seconds, tide clocks generally gain about 15 minutes per month, and must be reset periodically.
Tides also have an inherent lead or lag (lunitidal interval) that is different at every location, so tidal clocks are set for the time when the local lunar high tide occurs. This is often complicated because the lead or lag varies during the course of the lunar month, as the lunar and solar tides fall into and out of synchronization.

A tide table is used for more accurate tidal prediction, and shows the daily times and height of high water and low water for a particular location. Tide heights at intermediate times (between high and low water) can be approximately calculated using the Rule of Twelfths*, or even more accurately by using a published tidal curve for the location (when available).

* The Rule of Twelfths assumes that the rate of flow of a tide increases smoothly to a maximum halfway between high and low tide, before smoothly decreasing to zero again; and that the interval between low and high tides is approximately six hours. The rule states that in the first hour after low tide the water level will rise by one twelfth of the range, in the second hour two twelfths, and so on according to the sequence: 1:2:3:3:2:1
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Old 30-09-2011, 08:07   #4
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Re: Time and Tide Clocks

If you are sailing in one place, a time and tide clock might be of some use, but they are not as accurate as tide tables. In theory, you need to set the tide pointer once for your location, but I've never been in once place to see if my tide pointer stays accurate for months.

I have a chelsea time and tide clock with a quartz movement that came with the boat. I keeps really accurate time (5 secs/year), but when I really want to check the tide I use OpenCPN on my netbook. The tide function is nautical bling.
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Old 30-09-2011, 08:17   #5
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Re: Time and Tide Clocks

Those charming tide clocks that have a mechanical 12 hour 12 1/2 minute cycle can be off by an hour or more at various times each month. They track only the moon's influence, but the sun progressively throws the cycle off, until as you get back to the full moon the clock is accurate again.

There are some good iPhone/Android apps that will give you tide tables for stations all over the world. Most navigational software like OCPN and Navionics have embedded tidal information now, too. If you're cruising and changing locations often, something like that will be your best bet.
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Old 30-09-2011, 08:37   #6
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Re: Time and Tide Clocks

Usually I prefer the mechanical option; I certainly like ship's clocks and particularly the "Zulu time" 24 hour types. But a tide clock seems semi-useless to me in a new landfall situation and I would think that obtaining local information or using a quick calculator program would be a better bet.

If that's not your thing, you can simply hang out and observe. Six hours should do it.
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Old 30-09-2011, 08:44   #7
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Re: Time and Tide Clocks

These clocks have an additional hand that moves at a rate synchronized with the tide. Imagine that the tide hand follows the moon while the hour hand follows the sun. Thus the tide hand will tell you what stage of the tide you are at and whether the tide is flooding or ebbing.

The same info you can gather by looking at the moon and when the moon is not visible, by looking up the Sun&Moon data page on your GPS. If you take note of the data on one day, you will be able to calculate this same data for a good number of the following days.

IMHO tide clocks are sort of like a maritime souvenir - nice to have and mostly decorative.

A page of tides info from any relaible source will give you the same info, and more: the height and range of the tide and the phase of the moon which will tell you of what kind of tide you are having and what to expect over next couple of days.

In most areas, what may count way more than the tide is the tidal current of which the clock will tell you nothing, except that in local waters, once you know the tide, you also know the current.

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Old 30-09-2011, 08:44   #8
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Re: Time and Tide Clocks

Tide clocks are a cute novelty item but not something you would want to rely on. They approximate when but not how high.

Tide clocks do not work on the west coast of the US because we have semi-diurnal tides, meaning two lows and two highs every 24 hours and 50 minutes. I don't know which coast you are on. The east coast has diurnal tides.
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Old 30-09-2011, 08:58   #9
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Re: Time and Tide Clocks

This map shows the geographic distribution of different tidal cycles.
Coastal areas experiencing diurnal tides are yellow,
areas experiencing semidiurnal tides are red
and regions with mixed semidiurnal tides are outlined in blue.
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Name:	TideMap.gif
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Old 30-09-2011, 09:03   #10
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Re: Time and Tide Clocks

Nice map Gord.
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Old 30-09-2011, 09:17   #11
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Re: Time and Tide Clocks

If you have a Windows PC there is a freeware app called WXTide.
It's excellent and I use it constantly, as when the tide goes out here, it goes WAY out, like a couple of clicks.

It seems quite accurate and seems to agree with the likes of the Blue Chart Tide Tables, they give times within a few minutes of each other and it's also within a few minutes of the published tide tables for our location, so close enough for most purposes I think.
You set it up just once with your location. You can also run multiple instances with different locations if you need to (but you have to tick the right boxes in the config). I like it.

I've seen so called tide clocks and frankly they are more of a curiousity than something useful. They don't show dodge tides IIRC.

It's available here. WXTide32 - Tides and Currents for Win9x/NT

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Old 30-09-2011, 09:22   #12
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Re: Time and Tide Clocks

If you're serious about tides, there are smartphone apps that do an incredible job with tide predictions on a minute-by-minute basis. For tides I use TideGraph on my iPhone, and for currents I use the Navionics iPhone charts.
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Old 04-10-2011, 12:32   #13
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Sorry but there seems to be an under current of reliance on electrical equipment. Plotters and apps are great but can always let you down. You should be able to fall back on charts, tidal streams and tide tables. Sure I use them myself but I'd not even do a short Coastal sail without them as backups.
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Old 04-10-2011, 12:52   #14
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Re: Time and Tide Clocks

I just noticed it, the definitions.

http://oceanservice.noaa.gov/educati...07_cycles.html
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Old 04-10-2011, 12:57   #15
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Re: Time and Tide Clocks

A complete waste of money. Buy something useful like BEEEEER!

Jim
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