Pedant's definition of a spring tide?

[guernseyman]

....and it is probably telling that I have never seen any tidal publication that marks a tide as 'Springs'.

I forgot the obvious one: the local tide table booklet has a graphic down the left-hand side of the page for each month like a wave peaking at the two springs each month.

Visitors to Guernsey should be aware of that publication which is a mine of information, and available at all chandlers, etc. And it is free, although a donation to the RNLI is welcomed.

 

[Skylark]

Reeds Nautical Almanac marks each (single) spring and neap tide.

More broadly, tides in the spring cycle are described as 'springing', and those in the neap cycle as 'neaping'.

Clearly sime's definition is wrong, although it might apply in a location with small tides.

I agree with this, as I tried to say in an earlier post.

Interesting dialogue on the matter, though.

 

[Bandit]

Its more relevant to say we are in springs now or coming up to springs or coming off springs ie very big high tides and very low, low tides.

The opposite is neaps where the range is minimal.

A bit obvious but whether it is a spring or a neap tide makes a big difference not only to the height of a tide or the clearance over objects but the speed of the tidal flow eg the Alderney which varies hugely between spings and neaps.

Take the springs this year at the end of september for Guernsey
27th 9.5m and 1.1m
28th 9.9m and 0.6m
29th 10.1m and 0.4m
30th 10.0m and 0.6m
1st 9.6m and 1.0

All of those are big tides, sailing against the flows in certain areas is a no no. barometric pressure also makes a big difference as does wind direction.

With the naked eye and no tape measure its difficult to tell the tidal height differences between the 28th, 29th snd 30th.

 

[Simes]

Guernseyman Et Al,

Mine was not a definition but an explanation. It is possible in general terms to define the period of Springs as being when the range of the tide is within 0.5m of the mean Spring range. It is also possible to do this Neaps.

Just as a slight aside, here in central / northern Europe we do refer to tides with the greatest Range as Springs Tides and to tides with the least Range as Neap tides. Both terms come from ancient scandinavian words meaning respectively High Water and Low Water.

Simes

 

[Roberto]

Hi All,

I have been thinking: in the strictest sense of the term, when is a spring tide officially a spring tide?

i.e. Is there always only one spring tide per cycle or can you have multiple spring tides during a particularly springy spring? Also, is it possible to not have a spring tide at all during a particularly neapy spring?

another way of looking at the same phenomenon
in France every single tide (LW to HW) is given a "coefficient", a number which is roughyl proportional to the amplitude, range of that specific tide.
High coefficients mean high range, low coefficients small ranges.

Of course, they are referred to *ranges*, which is only loosely related to the absolute height of the HW or the LW, that is you may have the same range with a higher HW + higher LW, or a lower HW+lower LW

Here you can see an example of the monthly behaviour of coefficients.

Conventionally, the French HO defines Average Springs (Vives Eaux) those tides having a coefficient of 95, and Average Neaps (Mortes eaux) tides with a coefficient of 45.
Spring tides coefficients will hover around the 95 value, similarly neaps around the 45 mark.

For example, as the tidal streams tables give the two values of speed related to 95-45, looking at the coefficient will give an immediate idea of the type of current one might expect; much in the same way as range is used in the UK of course.



so
i.e. Is there always only one spring tide per cycle or can you have multiple spring tides during a particularly springy spring? Also, is it possible to not have a spring tide at all during a particularly neapy spring?


There are several spring tides during every cycle. In a particular springy spring they may have coefficients say around 100-115, in a neapy spring they may have coefficients say around 90-80. The long term average of the springy springs and of the neapy springs coefficients will yield a coefficient of 95, by definition.


not sure if it helps..

 

[Roberto]

I just checked the SHOM document: they define as Spring (vives eaux) every tide whose coefficient is above 70, neaps when below 70 (sounds logical, halfway between 95 and 45)
There is no special name for a coefficient 70 tide

 

[GlennG]

Always liked that French approach; so simple to know what's what in a simple number. Unlike us with our springy springs and neapy neaps.

Now I feel dirty

 

[Kawasaki]

Always liked that French approach; so simple to know what's what in a simple number. Unlike us with our springy springs and neapy neaps.

Now I feel dirty

Nah -- springy springs an neapy neaps is much more betterer
Than words with eux's an x's all over the place

Wash yer gob out GlennG
Then yer can speak proper like what I do

Fascinating thread chaps
Cripes! am I/ are We 'Anoraks'?
Do carry on though

 

[guernseyman]

Guernseyman Et Al,

Mine was not a definition but an explanation. It is possible in general terms to define the period of Springs as being when the range of the tide is within 0.5m of the mean Spring range. It is also possible to do this Neaps.

The trouble is, as I hinted, that here in Guernsey for example Spring tide ranges vary from about 6.8m. to about 10.0m. Thus the mean Spring range is going to be about 8.4m. and the largest Spring ranges are much more than 0.5m. away from the mean, as are the smallest, and many Spring tides would be excluded by Simes' definition, as I understand it.

 

[capnsensible]

Why not simply use the term 'mean' to describe an average spring tide and apply that to avoid confusion?

Ooops someone already has.....

 

[andygc]

Hope this doesnt sound like i'm trying to start an anchor-style argument: I am genuinely interested to know the answer.

Maybe not, but you succeeded.

 

[NormanS]

Back on Planet Earth, 'Spring Tides' happen every 2 weeks, alternating with 'Neaps'.

Springs go up higher & down lower than Neaps, so consequently flow faster to deal with the volume of water; on my half tide mooring there's actually more water around at half tide during Neaps.

!

I'm surprised at that. I would have thought that the one constant, barring changes in atmospheric pressure, and some local anomolies, would be the level at half tide.

 

[peterb]

There is an "Admiralty Manual of Tides" (NP120) which includes a definition of spring tide:

Spring tides are the greatest semidiurnal tides in a semi-lunation of 15 days. They are not necessarily the highest tides or the lowest tides, for these may be partially due to the diurnal tide. Spring tides are due to the reinforcement of the lunar semidiurnal tide by the solar semidiurnal tide, and occur when the high water of one is almost simultaneous with the high water of the other. The height of high water springs varies from month to month owing to the variations in the lunar and solar semidiurnal tides.

The manual is semi mathematical (about A level standard), but if you can understand it then (used together with the port tidal constants) it has everything necessary to write your own tide prediction program.

 

[GlennG]

http://en.wikipedia.org/wiki/Tide

Someone had to reference it...

 

[guernseyman]

I'm surprised at that. I would have thought that the one constant, barring changes in atmospheric pressure, and some local anomolies, would be the level at half tide.

That's true round here: half-tide rocks include 'demi' in their name and they are important because in the ever-changing marine scene they are awash at half-tide, come springs, come neaps.

 

[Roberto]

That's true round here: half-tide rocks include 'demi' in their name and they are important because in the ever-changing marine scene they are awash at half-tide, come springs, come neaps.

ah, that's where "demi de pas" or "demi de vascelin" come from...

I did not know that s interesting, thanks!

 

[NormanS]

In the good old days, charts used to give the HWF&C for ports on the chart. HWF&C means High Water, Full and Change, i.e. the time of High Water at the Full moon, and the New moon. From this you could, by interpolation, estimate the time of HW, at any time, of any year, provided that you knew the state of the moon.

Of course that was before the RYA wanted you to work out the tide heights to n decimal places.

 

[Roberto]

In the good old days, charts used to give the HWF&C for ports on the chart. HWF&C means High Water, Full and Change, i.e. the time of High Water at the Full moon, and the New moon. From this you could, by interpolation, estimate the time of HW, at any time, of any year, provided that you knew the state of the moon.

Of course that was before the RYA wanted you to work out the tide heights to n decimal places.

Brazilian charts still have it

 

[Kawasaki]

Maybe not, but you succeeded.

 

[timbartlett]

Of course that was before the RYA wanted you to work out the tide heights to n decimal places.

The RYA does not want you to work out the height of tide to n decimal places.

If you want an RYA certificate of Competence, however, it is not unreasonable for it to expect you to be able to demonstrate that you know how to use the tide tables -- something that is most easily done by getting the right answer.

On my Advanced Powerboat Instructors course, one of the examiners was Bill Anderson (the guy who effectively created the Yachmaster as we know it.) One of the questions involved working out the height of tide at a particular time at a secondary port. He and I faced eachother across the desk .... and he announced that my answer was not the same as his. "Of course, I said: you did yours with a sharp pencil and a ruler, I did mine by eye and with the edge of a fag packet." I passed.

PS I'd have said that a Spring Tide is the tide with the greatest range in any tidal cycle.