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Old 21-04-2007, 20:13   #1
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Tide and time.

I guess sometimes it just pays to surf the net.Has anybody used one of these? My thinking is the clock/tide thingie above would prove invaluble to the captain.Mudnut.
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Old 21-04-2007, 20:47   #2
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Yep, I've got one, and I reckon they're great. Principal use on my boat is when I go to anchor - knowing the state of the tide helps with how much chain to pay out. Also use it when transiting a passage with tidal flow. You can straight away see if the current is with, against or slack. The tide cycle on the clock is based on a straight six hour cycle (on my one anyway) and so the tide function needs a minor correction once a week or so.

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Old 21-04-2007, 20:57   #3
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Glad to hear Chris.So I take it that everyone else knew about them except me.The moment I saw it,I thought yep,I new it would come in mighty handy.Now if only it would make coffee and toast!!!Mudnut.
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Old 22-04-2007, 03:04   #4
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Tidal clocks should keep the average rate between high lunar tides, which occur about 12 hours 24 minutes apart. It’s important to first set your tide clock on the day of a full moon, as the moon has the dominating effect on the tides. Although the moon has a dominating effect on the tides, the sun also has an effect (46% that of the moon) and the elliptical orbit of the moon around the earth can change the tides by +/- 20%. To a lesser extent, the elliptical orbit of the earth around the sun has a similar effect. All of these factors not only affect the magnitude of the tides, but they also affect the actual timing.

Ocean-Clocks make tide clocks that are “localized” for specific coastal regions, displaying the major and minor ports, cities, towns and landmarks that suit various areas.
Ocean Clocks Time and Tide Clocks localised for your coast
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Old 22-04-2007, 05:30   #5
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Correct me if im wrong, wile crusing to a different latitude the tide clock will be off more and more as you travel, unless your postion stays the same or are traveling in a line of longatude?
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Old 22-04-2007, 06:19   #6
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Latitude has its biggest impact on the height of the tides. As you change longitude, the tide clock (the timing of the tides) would need constant adjustment. That all presumes that all tides operate on a semi-diurnal basis, which they don't. Sailors along much of the Gulf Coast, where diurnal tides (one high and one low per day) are common, would have little use for a tide clock that operates on a semi-diurnal cycle (two highs and two lows).

Because there are so many variables affecting the tides, I prefer to use tables/graphics that are easily generated on the computer or handheld devices (Palm, etc.)
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Old 22-04-2007, 06:30   #7
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Longitude has more effect on tide time than latitude. If you correct the clock to local time, then the tide will be about right.

You can estimate tide time without the clock if you figure that high tide is about 0800 local time on the morning of the full moon. Now "local time" is not just the time zone but calculated by longitude (4 minutes change per degree of longitude).

Then add 52 minutes change per day. That is the high tide will occur about 52 minutes later each day. You will be every bit as accurate as this clock.

Remember that tides are affected by local conditions as well and can only be predicted with much accuracy after a long period of observation. That is what tide tables have done.

None of this calculates tide height, but if you remember that the greatest tide change occurs at full and new moons (spring tides) and is least at quarter moons (neap tides) you will know whether today’s tide is likely to be greater or less than yesterday’s.

Break down and buy tide tables or computer software to get better predictions. If you are near an internet connection, there are several tide predicting sights available.

George
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Old 22-04-2007, 06:39   #8
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I may be wrong but I'm sure some areas like the Kimberleys and Shoalwater bay areas in OZ , that have 10 metre tides, have several tide changes a day, which would throw out the twice a day tide clock.

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Old 22-04-2007, 06:57   #9
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Then add 52 minutes change per day. That is the high tide will occur about 52 minutes later each day. You will be every bit as accurate as this clock.

If you want a tide clock that can account for more variables as well as changes in location (like when you are cruising). Try this computer based tide clock that is a totally free download:

WXTide32 - Tides and Currents for Win9x/NT

With this clock you can travel around and always be able to compute an accurate theoretical tide. Local conditions can effect tides so nothing is that perfect but as far as a theoretical computation this is as good as any published tide table you can pick up. This also is good almost everywhere in the world. If you check the web site close you'll find where you can download the enhanced map interface that lets you zoom into a spot and click on a tide station. The tide stations are the same ones you read in the newspaper for the daily tide times.

As noted above the mechanical tide clocks just add 52 minutes per day - period. I have one in the house and I reset it each full moon at high tide. It works fine but the calibration is based on the computer tide clock that matches the local tide authority here. I don't see mechanical tide clocks as very useful on board since your location changes and so does the calibration of the tide clock. The above program lets you set your timezone so you can use your own timezone to compute the tide.
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Old 22-04-2007, 07:09   #10
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Quote:
Originally Posted by Raven
Because there are so many variables affecting the tides, I prefer to use tables/graphics that are easily generated on the computer or handheld devices (Palm, etc.)
IF THE EXACT TIME OF TIDE STAGES IS ESSENTIAL, I SUGGEST YOU CONSULT A TIDE TABLE (with local offsets).

2007 Water Level Tidal Predictions:

USA: Tide Predictions
Canada: CHS-Tides, Currents, and Water Levels
UK & Ireland: NTSLF | Tidal predictions or NTSLF | Tidal predictions - high and low water times and heights
British Overseas & Independent Territories: NTSLF | Tidal predictions
Norway: Norwegian tidal and sea level data
New Zealand: LINZ - Analysis and Prediction of Tides
Australia: Tidal predictions - Marine safety - DPI - NT Government - Australia - Microsoft Internet Explorer

ONLINE TIDE PREDICTORS ~ Links: Tides and Tide Prediction

A little light reading:

The American Practical Navigator ~ Bowditch: Bowditch Online
Goto:
CHAPTER 9 ~ Tides and Tidal Currents: http://www.irbs.com/bowditch/pdf/chapt09.pdf

OUR RESTLESS TIDES ~ NOAA/NOS
A brief explanation of the basic astronomical factors which produce tides and tidal currents.
Goto: NOAA, Our Restless Tides, Explanation of Astronomical Factors, Tides and Tidal Currents
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Old 22-04-2007, 11:03   #11
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All that beautiful brass, and you eggheads start yapping about computers.

Sigh.

<w>
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Old 22-04-2007, 14:04   #12
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Twas quite entertaining living in North Fort Meyers (West coast of Florida). Two highs and two lows each day, with an average range of about 18" ... but ... a North or East wind could blow as much as 3' of water out, while a West or South wind could blow that much in ... during a sustained windy period, there appeared to be no tide at all! Had some "old salts" mighty confused!
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Old 23-04-2007, 00:31   #13
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Great info folks,I wasn't thinking about useing it for cruising,only local.Just so I know how high/low it is out there at a given time.Im a gonnabe,not a wannabe and couldn't think of a simpler instrument to help me in entering bars,channels and also in practising safe docking,Everybody knows its easier when the tide has stoped running.Although I don't think it's brass,I'm right into what CaptainJeff said.Mudnut.
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Old 25-04-2007, 10:37   #14
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My little Garmin handheld GPS76c has tides / moon phase data already in it for multiple locations. I assume most units have that as well.

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Old 25-04-2007, 16:04   #15
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I wasn't thinking about useing it for cruising,only local.Just so I know how high/low it is out there at a given time.
For home I would get one. They don't all cost a lot of money and if you reset based on the newspaper ayt the full moon they are quite handy. I tlike it when I leave the house as i know at mid tide if it is going to be going up or down when I come back. We have 3 feet here. Winds can add or subtract 2 feet. Hurricanes can make a lot more. Here on the Cheapeake the tide times can be more than 2 hours depending where you are. we live 1/2 mile from the Virginia Institute of marine Science and they get the prediction pretty close except when the wind blows hard and then no one gets it perfect.
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