the rising and falling of the ocean is caused by the
gravitational influences of the Earth-Moon-Sun and as the behavior of
orbits are known extremely accurately, so their influence on the oceans
However, as the
topography also has an
influence, each location has to have its own record of sea level behavior
using a tide-gauge.
By combining all this
accurate predictions for any date in the future, at a given location,
However, there are
factors such as changes in
seabed, rises in sea level, as well as the weather that will affect
behavior at any given time.
Tables generally give a
list of the maximum
and minimum sea levels heights and times for each day.
However, the heights
given are related to a
calculate the actual
depth of water at a
given point, add the charted depth to the height in the
Areas which dry will be
shown on the chart as
having negative values these should be subtracted from the tabulated
You must always check
that your charts and
tables are based on the same datum.
The most commonly used
‘lowest astronomical tide’ and ‘mean lower low
N. O. A. A. In the
United States uses the
mean-lower-low-water, MLLW, as its datum.
This means that some
tidal states may show as
having a negative height.
Most other national
agencies use the lowest-astronomical-tide (LAT) as their
The advantage of using
LAT is that all
tabulated heights are shown as positive numbers.
I am perfectly aware that the majority of Wooden Boat aficionados are sensible folk. However, I need to point out that I am an amateur wooden boat enthusiast simply writing in order to try to help other amateur wooden boat enthusiasts. And while I take every care to ensure that the information in DIY Wood Boat.com is correct, anyone acting on the information on this website does so at their own risk.