paulstevens
Well-Known Member
I reckon this is down to the weather. Pressure was pretty high on Saturday and it used to be said that an inch of mercury made a foot of difference on both low and high predictions.
Looking good for sailing tomorrow.....
- Thread starter FullCircle
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FullCircle
Well-Known Member
I beg to differ!
As you say in your last line - a rough guess - so if chart says there will be 1m and you have 0.5m rise of tide are you expecting to see 1.5m or do you just head for a bit of water blind and watch the echo sounder not knowing what is going to happen next? Presumably you had an idea that there was enough water in the spitway from the chart otherwise you wouldnt have tried it? Well thats what I do!
I differ.
Nudge up on expected best water, and chicken out when appropriate. No paper is involved.
Been through there hundreds of times, but this is first time this year. One good gale will negate any charted measurements one way or the other.
Saw a difference of 1.5m in a week of gales going across the Sunk to Ramsgate and back along the same track.
AliM
Well-Known Member
"I reckon this is down to the weather. Pressure was pretty high on Saturday and it used to be said that an inch of mercury made a foot of difference on both low and high predictions."
Nice theory, but the records (at Harwich anyway) show that the tides were precisely as predicted!
http://www.pol.ac.uk/ntslf/sadata_tgi_ntslf_v2.php?code=Harwich&span=2
Perhaps we'd better keep an eye on the depths at the Spitway, then. Tillergirl did a survey a year or two ago, which showed it was pretty flat with better depth slightly to the NE of the line between the buoys.
Since we all use it so often - can anyone who notices that it's shoaling let us all know!
Nice theory, but the records (at Harwich anyway) show that the tides were precisely as predicted!
http://www.pol.ac.uk/ntslf/sadata_tgi_ntslf_v2.php?code=Harwich&span=2
Perhaps we'd better keep an eye on the depths at the Spitway, then. Tillergirl did a survey a year or two ago, which showed it was pretty flat with better depth slightly to the NE of the line between the buoys.
Since we all use it so often - can anyone who notices that it's shoaling let us all know!
paulstevens
Well-Known Member
There are so many variables with all this but the above is based on local observations and by and large I have found it to be true. All my adult life of 40 odd years I have lived behind a sea wall and in the flood zone so have taken a very keen interest in local conditions.
These days my garden extends over the seawall to the noonday tide line but unfortunately that laps the wall so I cannot claim to have a private beach!
AliM
Well-Known Member
No, you misunderstand me. I agree entirely that high pressure leads to a drop in tide heights. We often see the pressure effect and then check on the website I gave to check that our observations were supported by their rather more reliable ones.
In theory, atmospheric pressure is about 30 ft of water and so a difference of 30mb is nearly a foot of tide. In practice, there has to be somewhere for that extra water to go to, so it doesn't always work out like that, and there are lots of other factors like the direction of the wind which can add to, or detract from, the effect on any particular day.
My point was, that on Saturday, the tide heights were exactly as predicted, according to the measured heights at Harwich (and Sheerness).
In theory, atmospheric pressure is about 30 ft of water and so a difference of 30mb is nearly a foot of tide. In practice, there has to be somewhere for that extra water to go to, so it doesn't always work out like that, and there are lots of other factors like the direction of the wind which can add to, or detract from, the effect on any particular day.
My point was, that on Saturday, the tide heights were exactly as predicted, according to the measured heights at Harwich (and Sheerness).