POLKA
sailing
YAC HT RAC I N G A N D
RYA T R A I N I N G C E N T R E
TIDAL THEORY
© Polka Sailing 2017
POLKA
Tidal Theory
s a i l i n g
Gravitational pull
Ferrous
The
gravitational
moon
metal
orbits
andthe
pull
magnetic
Earth
from over
the
fields
moon
a 28
will
day
and
affect
sun
cycle
iscreating
the main
compass,
Spring
cause
for
and
ofinstance...
tides
Neap tides
Neaps
Springs
Springs
Neaps
© Polka Sailing 2017
POLKA
s a i l i n g
Tidal Theory
Spring tides
...we experience
Ferrous
When
the
metal
gravitational
and
higher
magnetic
pull
highfrom
fields
waters
the
will
and
affect the
moon
lower
low
andcompass,
waters
sun are infor
line...
instance...
Greater range
of tide
© Polka Sailing 2017
POLKA
s a i l i n g
Tidal Theory
Neap tides
...we experience
Ferrous
When
the
metal
gravitational
and
lower
magnetic
high
pull from
waters
fieldsthe
will
and
affect the
moon
higher
and
lowcompass,
the
waters
sun are
foratinstance...
right angles to
each other...
Smaller range
of tide
© Polka Sailing 2017
POLKA
Tidal Theory
s a i l i n g
World tidal patterns
Ranges
Ferrous
Tidal
The
biggest
second
patterns
can
metal
differ
biggest
tidal
around
andrange
enormously
magnetic
is in
the
inthe
the
world
UK
fields
world
arewill
affect
very
is
within
in Canada
complex
the
a country
compass, for instance...
Bristol
Bay
of Fundy
Channel Collier Bay NW coast of
SE coast 1 – 3m
(mean range 12m)
13m)
Australia 10m
© Polka Sailing 2017
POLKA
Tidal Theory
s a i l i n g
Effects of weather
Strong winds for prolonged periods can
affect the tide
Push the water back
Hold
out making
makingthe
thetidal
tidal height
height
less than
greater
predicted
than predicted
© Polka Sailing 2017
POLKA
s a i l i n g
Tidal Theory
Effects of weather
Barometric pressure can affect the tide
Low pressure
High
pressure can
can make
make the
the tidal
tidal
height greater
less thanthan
predicted
predicted
© Polka Sailing 2017
POLKA
Tidal Theory
s a i l i n g
Tidal terms
Tidal terms
Chart
Charted
Depth
Neap
Mean
Spring
Highest
Clearances
Height
range
datum
High
Low
of
range
ofastronomical
depth
water
tide
light
Water
Water Springs
Neaps
Neaps
Springs
tide
Height of light
(above MHWS)
Clearance of bridge
(above HAT)
HAT
MHWN
Neap range
Height
of tide
Depth of
water
MLWN
Charted depth (below CD)
MHWS
Spring range
MLWS
Chart datum
© Polka Sailing 2017
POLKA
Standard Ports
s a i l i n g
Tidal heights
Tide tables
Ferrous
metal
areand
produced
magnetic
for fields
large will
affect the compass,
(standard)
ports such
forasinstance...
Port Victoria
VICTORIA
VICTORIA
© Polka Sailing 2017
POLKA
s a i l i n g
Standard Ports
Tidal heights
The tide
tablesThursday
contain daily
information
...for
example
3rd January
about the times and heights of high and low
water...
And
At
0043
0643
1301
at 1920
it’s predicted
the
height
prediction
the prediction
of tide
toisbe
5.7
isis
predicted
1.0
metres
0.8
metre
of
a metre
to be 5.5 metres
© Polka Sailing 2017
POLKA
s a i l i n g
Standard Ports
Tidal heights
...it’s
By
selecting
possiblethe
toappropriate
find the height
time
ofoftide
HWfor
and
a
the heights
time
of our of
choosing
HW andbyLW
using
for Victoria...
the Tidal Curve
© Polka Sailing 2017
POLKA
s a i l i n g
Standard Ports
Tidal heights
...it’s
By
selecting
possiblethe
toappropriate
find the height
time
ofoftide
HWfor
and
a
the heights
time
of our of
choosing,
HW andby
LWusing
for Victoria...
the Tidal Curve
© Polka Sailing 2017
POLKA
s a i l i n g
Standard Ports
Tidal heights
What will be the height of tide at Victoria on
Thursday 3rd January at 1540 UT?
© Polka Sailing 2017
POLKA
s a i l i n g
Standard Ports
Tidal heights
Enter HW time and fill in the boxes for each
hour after HW
1301 1401 1501 1601 1701 1801 1901
© Polka Sailing 2017
POLKA
s a i l i n g
Standard Ports
Tidal heights
Mark in
the aheights
of HW and
LW...
...and
draw
line between
them
1301 1401 1501 1601 1701 1801 1901
© Polka Sailing 2017
POLKA
Standard Ports
s a i l i n g
Tidal heights
In this
Find
Draw
...then
...continue
1540
aexample
draw
lineUT
the
upwards
across
online
the
theup
to
height
bottom
until
meet
to the
itofthe
meets
scale
HW
tide
HW/LW
scale
will
thebe
curve...
line...
approximately 3.7m at 1540 UT
(1540 UT approx)
1301 1401 1501 1601 1701 1801 1901
© Polka Sailing 2017
POLKA
s a i l i n g
Standard Ports
Tidal heights
...when
It’s
also will
possible
the height
to findofout
tide
when
at Victoria
a specific
fall
height
to
2.5 metres?
of tide will occur...
1301 1401 1501 1601 1701 1801 1901
© Polka Sailing 2017
POLKA
s a i l i n g
Standard Ports
Tidal heights
Draw
linedown
down
from
the
HW
scale
it
In
...then
...continue
thisaexample
draw
across
the
to
to
height
the
meet
bottom
of
the
tide
curve...
scale
willuntil
fall to
meets
HW/LW line...
2.5m atthe
approximately
1640 UT
1301 1401 1501 1601 1701 1801 1901
© Polka Sailing 2017
POLKA
s a i l i n g
Standard Ports
Tidal heights
...the
unbroken
red
representing
Springs,
A decision
had to
beline
made
regarding which
or
the
blue
for Neaps
part
ofbroken
the curve
toline
use...
1301 1401 1501 1601 1701 1801 1901
© Polka Sailing 2017
POLKA
s a i l i n g
Standard Ports
Tidal heights
The the
Spring
lineSpring
used
on this occasion,
...is
...5.7m
–mean
0.8m
=was
4.9m
range
range...
because the range for this time period...
1301 1401 1501 1601 1701 1801 1901
© Polka Sailing 2017