Why is HT at Springs always at lunchtime?

[DaveParry]

I think I am being really stupid here. I was having a conversation in Conwy at the weekend and someone mentioned sailing was better around neaps because you could go out in the morning and come back in the evening.

At first I thought this was something to do with tide heights, timings of gates etc., but on closer examination I see that at Springs, HT is always around lunch and at Neaps it is always morning and evening.

I thought the timing of tides was governed by the lunar cycle (28 days) and was nothing to do with the diurnal one (24 hours). I have just realised that I may have missed something all this time. Can someone enlighten me? Thanks.

 

[graham]

Its different in different places .Our springtides are usually around 8 to 9 AM/PM

 

[fluffc]

It is a myth that springs are always at the same time of day, as they do move on ever so slightly each fortnight (about 15 minutes per year). So generally you will notice that 'springs' and 'neaps' fall at certain times of day, but there is no hard and fast rule.

 

[BlueSkyNick]

Its the same in the Solent - 50% of the time. The other 50%, spring high tide is around midnight !! /forums/images/graemlins/wink.gif

both with up to an hour either way during the year.

 

[graham]

They dont move on much in this part of the world???

Springs have been in the morn/evening as long as I can remember.

 

[cnh]

Springs happen when the sun and moon are in line. If you think about it, this will be when the sun and moon are directly overhead [midday], or, as at the moment, on opposite sides of the earth. The bulge will again be at the noon position.

Nicholas Hill

Channel & Baltic Guide

 

[graham]

Nice theory but Springs occur at different times of day in different parts of the country.

check this weeks tide table for Cardiff. biggest Tides occur at around 0800 . tide tables

 

[awol]

The following give you an approximate answer to tide times - so out with your tide tables and see how far out they are!

 

[Skyva_2]

That is true in the Solent but other locations have Springs at different times

The UKHO explanation is:

"Why do Spring High Tides always seem to occur at the same time of day in the same place?
The reason is that when the New and Full Moon occur, the two major
semi-diurnal constituents (M2 and S2) of the tide raising force are
precisely in phase. Consequently, High Water Springs will always occur at
about the same time of day."

Which is too concise for me!

I have lifted the quote under from uk.rec.sailing in Nov 2006 where there was a long thread on the subject, if you care to search further:

"Imagine a clock synchronised to the moon instead
of to the sun. It would read 12 o'clock whenever the moon transits
your local meridian (both above you in the sky ("lunar noon") and below
you on the other side of the Earth ("lunar midnight")). Obviously this
clock would need to run a little slower than our normal solar clocks.
In fact the speed ratio of lunar to solar clock would have to be about
28.53:29.53.

Then if things were simple (which they're not, but bear with me),
HW would always be at exactly the same time on this lunar clock,
for any given location.

Because lunar and solar clocks run at different speeds, they drift
with respect to each other, and every now and then the solar one,
being the faster of the two, "overtakes" the lunar one while
displaying the same time. This happens twice a month, at the full
and new moons.

Now because springs happen at (or a little after) full and new moon,
and if that is when the two clocks show the same time, it follows
directly that if HW is always at (say) 4 o'clock on the lunar clock,
then spring HW will always be at 4 o'clock solar time.

As you have noted, the spring HWs are not always at *exactly* the same
solar time, but they vary by a few hours around this key time. This
variation comes from interference by other species of tide, i.e.
those with speeds other than 30 and (about) 28.984 degrees per hour.
These other species arise from a number of factors which complicate
matters, notably the fact that the orbits of the moon and Earth aren't
perfectly circular nor co-planar, nor co-planar with the Earth's
plane of rotation."

 

[Lakesailor]

I thought lunch was a moveable feast anyway.

As for Vulgar Establishments. I've been to some of those, but it was usually later in the evening, or to be more accurate, Sunday lunchtime. So perhaps there is some truth in the theory.

 

[cnh]

The reason springs happen at different times in different parts of the country is due to the land constricting the hump of water under the sun/moon. If there were no land in the way, springs would indeed be at midday and midnight. In say, Cardiff, the tide is delayed by the Severn estuary. Similarly in the North Sea - the UK gets in the way, and the hump has to make its way round.

Nicholas Hill

 

[TheBoatman]

In my part of the world - Kent - MHWS are always around midday/midnight and neaps are 06.00 & 18.00hrs - that's not to say exactly, just a rule of thumb.
So if I see a HW at (say) 09.00 it was a neap but is heading towards a spring.

Peter.

 

[Kawasaki]

As said it's different around the Country.
Just happens were you are (and Me) it is predictable that High water Springs are "Mid day" ish and High water neaps "Tea time" ish.
However if You make a mental note of this it can help You plan Your Sailing activities, locally.
So if You want to get in and out of Conwy during neaps cos there's less water "going on". Nip out at 7.00 am 1 hour after high water! get a push out to Puffin or wherever. Hit the Fairway bouy at 15.30 hours, back in time for Tea!
I have always used "Lavers" Liverpool tide table for Our area.
Since a kid digging bait on Rhyl beach for Summer Holiday money during the 50's, had to know what the Tide was doing case I got cut off from land!
Still think in Ft,can't handle metres,glance at the little book and if it says 27ft Livepool or 25ft or 31ft etc etc can immediatley suss out if we are on Springs ,Neeps or when high or low water is and when I can get out or get back in to PD and which way the current is flowing etc.

 

[Birdseye]

Cant you get to sleep either?

Anyway, as I understand it, tides are a sort of resonance effect. In other words, think of lifting up the half full washing up bowl - the water in it will slosh from side to side with a certain rhythm. The rhythm depends on the size of the bowl which is one reason why you have very small tides in the med.

This sloshing is in response to the pull of the sun and moon, and when the timing is right the pull is greatest. Imagine your kid on a swing - time your pushes right and the swing goes higher, time them wrong and the swing goes lower.

The strong pulls are when the sun and moon get nearest to being in line and with the direction of push or pull near vertical - hence twice a month when the moon on a 28 day cycle catches up with the earths 24 hour rotation

The time when this tidal flow of water gets to various places depends in part at least on the shape of the land. Since that doesnt change, the times when hw gets to a certain location at springs doesnt change much either.

Sure there are all sorts of secondary effects causing fluctuations around the typical time for a locality, but the fluctuations arent great - maybe an hour or two in either direction.

Interestingly, the first person to work out mathematically what the tides were doing was Newton.

 

[alant]

"It is a myth that springs are always at the same time of day, as they do move on ever so slightly each fortnight (about 15 minutes per year). So generally you will notice that 'springs' and 'neaps' fall at certain times of day, but there is no hard and fast rule."

From 'Yachting & Boating Book of Navigation", published 1967,
"High water at Dover is about 20mins past 11 nearest to the time of the new & full moon. If full moon is at noon, high water will be at 11.20am on that day."

 

[ronsurf]

The first person to apply the method of harmonic constituents that we still use today was Laplace, an astonishing French mathmatician. He calculated that any tide curve could be represented by the sum of a series of sine waves (the chief ones being that generated by the moon, M1, and the sun, S1) plus others for less influential astronomical effects (recession of the moon's nodes, and wobbles in its orbit), and some more for shallow water effects depending on where you are geographically. These are the ones the UKHO won't let anyone have unless they pay... Here in Plymouth spring tides coincide with teatime (about 5pmish), the reason for the differing times around the coast is that it takes a while for the tidal wave to propagate along the coast, due to friction of the shallow water.

 

[AuntyRinum]

[ QUOTE ]
Springs happen when the sun and moon are in line. If you think about it, this will be when the sun and moon are directly overhead [midday],....

[/ QUOTE ]
If only it was that simple.

 

[LymingtonPugwash]

All these theories are rubbish.... you can't blind me with the truth!
HT at springs hits at lunchtimes at it's The Almighty's way of giving sailors a greater incentive to stay out of pubs at lunchtime by giving perfect tides to go out in the morning and coming back in the evening. /forums/images/graemlins/smirk.gif

 

[Channel Ribs]

Good theory, however. How do you explain The Royal Oak at Langstone in Chichester Harbour? Which can *only* be reached at high tide, is it perhaps (as some have suspected for while) the seat of Satan himself?

/forums/images/graemlins/smirk.gif

 

[Roberto]

South brittany

here HT springs usually happen in the early morning and late afternoon, while at neaps they are usually around midnight and noon


a nice booklet is distributed by chandleries or shipyards, mareegraf

where it can easily be seen from dark blue and light blue colours