en>Sobarwiki: anti-stokes less probable

2013-11-08T17:10:29Z

anti-stokes less probable

← Older revision		Revision as of 19:10, 8 November 2013
Line 1:		Line 1:
	~~Jayson Berryhill~~ is ~~how I~~'~~m known as~~ and ~~my spouse doesn~~'~~t like it at all~~. ~~Office supervising is where her primary earnings arrives from but she~~'s ~~currently utilized for~~ another ~~one~~. ~~I am truly fond~~ of ~~handwriting but I~~ can~~'t make it my occupation truly~~. ~~Her family lives~~ in ~~Ohio.~~<br><br>~~Here~~ is ~~my website - accurate psychic predictions (~~[http://~~formalarmour~~.~~com~~/~~index~~.~~php?do=~~/~~profile~~-~~26947~~/~~info~~/ ~~simply click~~ the ~~following webpage~~])		[[File:Rule of twelfths.PNG\|thumb\|right\|Rule of twelfths]]
			The '''rule of twelfths'''<ref>[http://www.diy-wood-boat.com/Rule_of_twelfths.html Rule of Twelfths for quick tidal estimates<!-- Bot generated title -->]</ref> is a [[rule of thumb]] for estimating the height of the [[tide]] at any time, given only the time and height of high and low water.<ref>The Outboard Boater's Handbook: Advanced Seamanship and Practical Skills, written by David R. Getchell, published by International Marine, page 195, ISBN 978-0-07-023053-8</ref> This is important when navigating a [[boat]] or a [[ship]] in shallow water, and when launching and retrieving boats on [[slipway]]s on a tidal shore.

			The rule 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.<ref>The weekend navigator: simple boat navigation with GPS and electronics, written by Robert J. Sweet, page 162, ISBN 978-0-07-143035-7</ref>

			==Example calculation==
			If a [[tide table]] gave us the information that tomorrow's low water would be at noon and that the water level at this time would be two metres above [[chart datum]] and further, that at the following high tide the water level would be 14 metres. We could work out the height of water at 3:00 p.m. as follows:

			*The total increase in water level between low and high tide would be: 14 - 2 = 12 metres.

			*In the first hour the water level would rise by 1 twelfth of the total (12 m) or: 1 m

			*In the second hour the water level would rise by another 2 twelfths of the total (12 m) or: 2 m

			*In the third hour the water level would rise by another 3 twelfths of the total (12 m) or: 3 m

			*This gives us the increase in the water level by 3:00 p.m. as '''6 metres'''.

			This represents '''only''' the increase - the total depth of the water (relative to chart datum) will include the 2 m depth at low tide: 6 m + 2 m = 8 metres.

			Obviously the calculation can be simplified by adding twelfths together and reducing the fraction beforehand i.e.

			Rise of tide in three hours <math>=\left({1\over12}+{2\over12}+{3\over12}\right)\times 12 \ \mathrm{m}=\left({6\over12}\right)\times12 \ \mathrm{m}=\left({1\over2}\right)\times12 \ \mathrm{m}=6 \ \mathrm{m}</math>

			==Caveats==
			The rule is a rough approximation only and should be applied with great caution when used for navigational purposes. Officially produced tide tables should be used in preference whenever possible.

			The rule assumes that all tides behave in a regular manner, this is not true of some geographical locations, such as [[Poole Harbour]]<ref>http://www.shrimperowners.org/sitefiles/Poole%20Tides.pdf</ref> or the [[Solent]]<ref>[http://www.bristolnomads.org.uk/stuff/double_tides.htm English Channel Double Tides<!-- Bot generated title -->]</ref> where there are "double" high waters or [[Weymouth Bay]]<ref>http://www.visitweymouth.co.uk/downloadForms/TideTables2010.pdf</ref> where there is a double low water.

			The rule assumes that the period between high and low tides is six hours but this is an underestimate and can vary anyway.

			==References==
			<references/>
			{{Physical oceanography}}

			{{reflist}}

			{{DEFAULTSORT:Rule Of Twelfths}}
			[[Category:Rules of thumb]]
			[[Category:Tides]]

			[[de:Gezeitenrechnung#Zwölftel-Regel]]

93.35.55.107 at 13:20, 11 July 2010

2010-07-11T13:20:16Z

New page

Jayson Berryhill is how I'm known as and my spouse doesn't like it at all. Office supervising is where her primary earnings arrives from but she's currently utilized for another one. I am truly fond of handwriting but I can't make it my occupation truly. Her family lives in Ohio.<br><br>Here is my website - accurate psychic predictions ([http://formalarmour.com/index.php?do=/profile-26947/info/ simply click the following webpage])

Stokes line - Revision history

en>Sobarwiki: anti-stokes less probable

93.35.55.107 at 13:20, 11 July 2010