Boating and Sailing.pdf - Moja ladja

Chapter 16: Mastering the Tides
that creek at low tide. You’re locked in until the next high tide, so keep that in mind any
time you go exploring in the shallows.
The tide tables also list nearby locations with time corrections for the nearest main
reporting station. They list the latitude and longitude of the location so that you can confirm
with your GPS, and the difference in time from the nearest station. The difference
may be anywhere from a few minutes to several hours, and is not the same for high and
low tides. You subtract minus differences and add positive differences.
For example, suppose you want to figure out the tide for a fishing spot that’s 15 miles up
your favorite bay from the mouth, and the tides are only reported in the tables for the
mouth. Say the report indicates a noon high at the bay mouth, and a +2.0 hours time difference
for your fishing location. You would figure it this way:
12:00 + 2 = 2:00 P.M., the time of high tide at your spot
There are very slight variations in tide height at various locations on a given tidal period.
In most of the southeastern United States, this difference is insignificant, but in the
northeast it can be considerable. The tide tables
list this variation as well, and it should be considered
if you’re making an iffy passage across a
bar.
Bridge Clearance
Do you ever need to know the tide heights if
you’re not crossing a shallow bar? Maybe.
It could be that problems arise above the water. A
low bridge can block passage for fly-bridge cruisers
and sailboats on high tide, yet let them pass
with space to spare on low. Sometimes even runabouts
can be blocked by low-hanging roadways.
You obviously need to know your boat’s bridge
clearance if you navigate anywhere that passage
beneath one of these structures is common. The
bridge clearance (BC) refers to the height from
the waterline (where the surface meets the hull)
to the highest point of any structure on the boat,
including the mast, tuna tower, or outriggers. (If
your radio antennas and riggers fold down, you
don’t have to measure them in the equation.)
227
Boat Bytes
It’s always best to punch
around in the backwaters
on a rising tide, and to
head back for deeper
water shortly before the
tide peaks and starts to run back
out. That way, if you go aground
inside, the rising water gives you
a good chance to get off and
escape; while if you ground on
falling water, you’re stuck until
the next incoming tide.
Boater-ese
Bridge clearance (BC) is
the distance from a boat’s waterline
to the highest point on the
topsides. It indicates the height of
a bridge under which a boat
can pass.