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Spring Tides


Gnasher
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I have been trying to understand when spring tides occure. Do we get these every month, how often, etc? Is there any useful sites that I can use that will help me determin what location i choose. I have checked out one web site and it says that 2morrows high is 1.7m. Is that a big tide a small tide or what?

 

It aslo says that Hurst is 2.2m and xchurch entrance is 1.7m. why the difference when its only a few miles apart.

 

Is tommorrows a big tide at the back of the island? The post all sounds a bit stupid and basic, but its stuff i need to know.

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A simplified version...........

 

NEAPS Less water moving and not quite so high or low as a spring

 

SPRINGS Most water moving, higher highs and lower lows

 

THE HIGHT GIVEN is always a 'prediction' not a certanty. This is because beside the movement of the moon, air pressure affects the hight/flow of water.

eg .. High air pressure (light winds) presses down on the water surface and suppresses the tidal flow.

 

Low air pressure (stormy weather) With less pressure on the waters surface the level and speed of flow can 'Surge' creating tidal flooding conditions in very low pressure storm centers.

 

WATCH THE MOON blink.gif Full or new moon = Spring tides

 

Half moon (and degrees of) = Neap tides.

 

The tide hight given is the hight OVER the 'chart datum' . The chart datum is basically the LOWEST tide you could ever expect in that area. Thats why you see lots of drying areas on a harbour chart and yet you might never have seen the water that low.

 

Differences in hight for a given area.........

 

Some areas 'pinch' the flow of water so that the same amount of water has to pass through a narowing channel, this speeds up the flow AND as the water can only move upwards in hight for the given area it has to flow, the depth of the water over the chart datum increases. The perfect example is the Bristol Channel where they get 20 t0 40ft tide hights as the channel narrows.

 

A full 12 hour of tide progresses at 20 min per 12 hour low to high to low again tide.

 

eg Low water Monday 12 noon

 

Low water Tuesday (24hrs = 2 full tides X 20min per tide = 40 min) 12.40pm

 

All of the above is generalisation and the purist will happily pick minutia out of it, but it all one needs to have a good working knowledge of the tide around OUR coast.

 

Oh and lastly the EQUINOX's Simplified, these occure one in the SPRING and one in the AUTUMN, and very roughly coinside to the week we put the clock forward or back an hour. These equinoxal tides are when the pull of the moon, the sun, and the Mirror blink.gif are in line and give us the highest highs and lowest lows of the year.

 

 

Any further explination can be obtained by sitting in a bath full of hot water and playing with your duck whilst sliding from one end of the bath to the other ohmy.gif

 

Mad Mike

 

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Jeepers guys,

 

If any of you try that demo of Mike's, for goodness sake make sure you stow the soap securely before taking action........... blink.gif

 

There should be an HSE report on this............... sad.gif

 

 

My duck is at the vets weep.gif

 

 

and my keel might be damaged dry.gif

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