When exactly is a spring tide?

[Midnight Drifter]

I am trying to understand the lag of tides - in other words, how and why spring tides occur some time after full moon and new moon, and not at the time of the full moon (and similarly for neaps after the quarter moon). To do that, I need to know when spring tides occur - the date and time. Is it possible to state this?
My understanding is that a spring tide is defined as the tide with the largest range. But sometimes more than one tide has the largest range - e.g., at Dover in January 2022 (I happen to have the 2022 edition of Reeds Almanac to hand), full moon was on 17th January, the highest HW was 6.5m which occurred on the 22nd and 23rd, the lowest LW was 1.2m which occurred on the 19th, 20th, 21st and 22nd, and the largest range was 5.2m which occurred on the 20th, 21st, 22nd and 23rd. So, when is the spring tide? Why does Reeds say it is on the 20th?
To know how long the lag is, it is necessary to know the time of the full moon and the times of the spring tide. In the example above, full moon was at 2321 on 17th January. So, if springs is at an unknown time on the 20th, the lag could be anything between just over 2 days to just over 3 days. Is it possible to state the time of a spring tide, as well as its date?
I am NOT asking about the time of HW at springs, which varies from place to place, but about the time at which tides all over the world are at their greatest.

 

[wonkywinch]

Does this help understanding? - Amphidromic point - Wikipedia

 

[MoodySabre]

Round here they are just after lunch. Simple folk on the East coast.

 

[Midnight Drifter]

Does this help understanding? - Amphidromic point - Wikipedia

No, sorry, it does not answer my question at all.

 

[Midnight Drifter]

Round here they are just after lunch. Simple folk on the East coast.

Yes, HW at springs occurs at a similar time of day at a certain location. At Oban HW springs is around 0600. But my question was not about the time of HW at springs, which varies from place to place, but about the time at which tides all over the world are at their greatest.

 

[rogerthebodger]

Tide Hight and flow does depend on the arrangement of the underwater conures and how the water flows around the conures.

At one point in a harbour we get 2 high tides every cycle and this is due to the flow through a narrow entry to the harbour lagoon

 

[johnalison]

It all depends on the Establishment of the Port. According to Wikicheat:
Establishment of a port is the technical expression for the time that elapses between the moon's transit across the local meridian at new or full moon at a given place and the time of the next high water at that place. As an example in the UK, the interval (constant at any one place) may vary from 6 minutes (Harwich) to 11 hours 45 minutes (North Foreland) meaning that the time difference of high water between those two places is 21 minutes. At London Bridge it is 1 hour 58 minutes.[1] The term establishment of the port is identical to the obsolescent term High Water Full and Change (HWF&C) Full referring to the full moon and change referring to the new moon[2]. Before the creation of modern tide tables, it was a quick way of predicting the time of local high water. The moon’s passage at the local meridian is about 50 minutes later each day. If it is HWF&C 1 hour 30 minutes and we are three days after the full moon, then the morning high water is 1h 30 + 150 minutes = 0400[3].

 

[B27]

Yes, HW at springs occurs at a similar time of day at a certain location. At Oban HW springs is around 0600. But my question was not about the time of HW at springs, which varies from place to place, but about the time at which tides all over the world are at their greatest.

The shape of tidal curves is basically close to a sine wave, in a simple case where tides are not much affected by Islands and what have you.
When Islands or coasts affect the tidal flow, the curve changes shape, this can be expressed as 'harmonics' on the fundamental wave.
The more harmonics, the more you depart from the simple model of a neap tide being a small sine wave and a spring tide being the biggest.

I would assume that a Spring tide day is a spring tide day everywhere, and if the largest mass of water moving up and down the channel doesn't actually cause the highest or lowest tides everywhere, then those don't need to occur on 'spring tide day'.

You get variations in curve shapes between springs and neaps, and a table of tidal differences for a secondary port shows different time differences between springs and neaps.

Personally I always take the phrase 'spring tides' to mean a period of a few days centred around the biggest predicted tides, not just one day or one high tide.

And it's not worth getting stressed about the odd few cm in predictions as the weather can changed things by a foot or more.

 

[NormanS]

Before the days of instant info, and the requirement to know the tide time to the nearest minute, and its height to three decimal places, as johnalison has reminded me, BA Charts used to give the time of HWF&C for ports on a chart. It was expected that seafarers would have a pretty good knowledge of the state of the moon, and so without the requirement for tide tables, far less the internet, they were able to estimate the state of the tide at any time.
I have never considered that one particular tide is A Spring, rather that tides were at "Springs" or "Neaps", or somewhere in between.

 

[johnalison]

I tend to use the simplistic “top of springs” for the day with the highest/lowest tide. Springs or neaps for me are any of the days when the tides are either somewhat extreme or somewhat moderate. What we now need is a word to cover the days when it is neither springy nor neapy.

 

[MontyMariner]

how and why spring tides occur some time after full moon and new moon, and not at the time of the full moon (and similarly for neaps after the quarter moon)

The height of the tide is mainly influenced by the moon's magnetic field, it takes time for that influence to be seen in the tide height, the difference is about two days, hence the max high and min low is seen a couple of days after the new and full moon.

 

[rogerthebodger]

moon's magnetic field,

Don't you mean the gravitational field the gravitation attraction of the moon and the sea water

 

[PCUK]

About every fortnight is what you are asking I believe.

 

[MontyMariner]

Don't you mean the gradational field

Oops! Yes gravitational field

 

[Rhylsailer99]

The sun pulls a bulge of water that moves because the planet rotates, sometimes the sun and moon are together causing a larger tide , ie spring tide and a black new moon , the other set of tide the moon and sun are opposite sides to earth and the moon can be seen lit by the sun these are neap tides.

 

[johnalison]

Oops! Yes gravitational field

That’s a shame. I thought it was a good joke.

 

[LittleSister]

The height of the tide is mainly influenced by the moon's magnetic gravitational field, it takes time for that influence to be seen in the tide height, the difference is about two days, hence the max high and min low is seen a couple of days after the new and full moon.

Yes, the OP clearly knows that, but is asking why there is such a lag.

I have never fully understood it myself. All the explanations I've heard or read to date - usually mentioning the inertia of the mass of the oceans and seabed / landmass constraints - are insufficiently specific to fully satisfy me.

That said, it seems to me (and I'm happy to be corrected) that -
(a) if it were only the inertia of the mass of the oceans and seas, the maximum springs and minimum neaps would be, in principle, the same lag (36 hours, say) everywhere from that cause; but
(b) the seabed / landmass constraints could then explain why particular localities' tides vary both either side of that worldwide average 36 hours (or whatever it is), and also between different height high or low tides; but also
(c) the seas and oceans aren't an undifferentiated mass (as assumed in (a) above), so the effect of their overall inertia will also be affected by the sum total of all the seabed / landmass constraints, and vary in time (and height) either side of the average, 36 hours (or whatever it is).

 

[LittleSister]

Tide Hight and flow does depend on the arrangement of the underwater conures and how the water flows around the conures.

That's a new one on me.

So underwater Central and South American Parakeets (typically having green plumage with patches of other colours, no less) are the explanation!

 

[Frank Holden]

How you say 'its complicated'?.
Doesn't seem to be a lag where I keep my boat
Tide Times and Tide Chart for Puerto Montt
And a 'Tide Predicting Machine' in the maritime museum at Tigre, Buenos Aires.

 

[wonkywinch]

This is the Calshot one ..