In the main a spring tide occurs 2 days after the date of New and Full Moon. However,
a Spring Tide can occur anywhere from 0 to 4 days after New and Full Moon - it just
depends upon the geographical location of the tidal station concerned and how the
tide-generating forces are affected by friction on the surface of the earth.
Furthermore, there are certain places, mainly in the Pacific, where Springs appear
to occur before the date of New and Full Moon, but what is actually happening
is that the Spring Tide occurs between 11 and 14 days after the previous
New or Full Moon.
Fundamentally, it is the characteristics of the local tidal regime which result
in the Spring Tide occurring after the instant at which the tide raising forces
are at a maximum (i.e. at New and Full Moon).
From the harmonic analysis of tidal observations we can determine how the individual
harmonic constituents (which combine to create the tidal regime) behave relative
to their theoretical astronomical values. It then becomes a matter of cause and
effect, where the resultant effect always occurs after the force has been
The constituent phase will always lag behind the theoretical (astronomical) value,
and it is the combination of inertia and friction associated with the water mass
which gives rise to the phase lag.
The two main constituents which influence our tides around the UK are the Moons
semi-diurnal and the Suns semi-diurnal constituents, M2 and S2 respectively. The
harmonic analysis provides us with the phase lag of these two constituents behind
their astronomical values from which we can determine the occurrence of the maximum
height of the Spring Tide after the time of New and Full Moon. This is also
known as the Age of the Tide.
This occurs on average 2 days after New and Full Moon but, for example, it can be
as much as 3 days after at London Bridge and only 1 day after at Dublin depending
upon the local tidal regime.
A more comprehensive explanation can be found by consulting any authoritative textbook
on tidal theory. Our own Admiralty Manual of Tides (NP120) may possibly be found
in a local reference library, otherwise it can be obtained via your local
Admiralty chart agent or chandler.