Tides for Kayakers
Exeter Canoe Club
What are Tides?
Movement (horizontal and vertical) of water on the surface of the earth
caused / affected by:

Gravitational pull of (primarily) the moon, but also the sun.

Rotation of the earth

Effect of land masses
Effects of Moon and Sun.
Note: tides in UK are semi-diurnal, i.e. 2 tidal cycles in 24 hrs
Where our tides are generated
Some Definitions
1.
Spring tides: full / new moons; big ranges; fast rates.
2.
Neap tides: half-moons; small ranges; slower rates.
3.
Slack tide: pause between tides, little water movement.
4.
Tidal height: height of water above chart datum.
5.
Tidal range: difference in tidal height between HW and LW
6.
Tidal stream: horizontal flow of water
7.
Tidal set: direction of stream
8.
Tidal rate: speed of stream
9.
Drift: where a kayak is carried by the tide
Example of a Tide Table
Note: moon symbols; times advance by around 1hr each day; time zone.
Big Springs and Little Springs
Dover Spring Ranges. Note range can be 4.5 – 6.3m
Date
14 Jan
29 Jan
13 Feb
28 Feb
14 Mch
29 Mch
HW
6.1
6.5
6.2
6.8
6.2
6.8
LW
1.4
1.0
1.3
0.6
1.2
0.5
Range
4.7
4.5
4.9
6.2
5.0
6.3
Top Tip
Time of High Water Spring (HWS) in any one place is always the same.
For example HWS at Exmouth Dock is always approximately 0600 and
1800 hrs.
So if it’s a Full / New moon you know you can paddle down the river in
the evening.
This is an example of a Tidal Constant
Dover Tidal Curve
Dover Tidal Ranges: 4 weeks
Tides, Poole Harbour
Rule of Twelfths
Note: maximum water movement during middle third of 6 hour half-cycle, tailing off
either side.
Hour
Amount of water in hour
Cumulative water
movement
1
1/12
1/12
2
2/12
3/12
3
3/12
6/12
4
3/12
9/12
5
2/12
11/12
6
1/12
12/12
Charted Depth
= depth at Lowest Astronomical Tide (LAT)
= Chart Datum
.
Range = 4.2m
Need 2m of tidal height
= 6/12 of range
Achieved 3hrs after LW
(19:00 hrs +)
Tidal Streams
Flood Streams Around UK
Charted Rates Always in Knots
•
1 knot = 1 nautical mile / hr
•
1 nautical mile = 1.85 k, or 1.15 miles
•
1 nautical mile = 1 minute of latitude
Tidal Atlases
Tidal Atlases
Streams measured at charted points
(Tidal Diamonds)
Pilots for Local Detail
Charted Rates are Averages.
Actual rates can be more, or less, depending on tidal range. Dover
spring range can be 4.7 – 6.5m
Rough Estimations of Rates: 50/90 rule
Hrs B/A Slack
0
1
2
3
4
5
6
% Max Rate
0%
50%
90%
100%
90%
50%
0%
Example 2 k
charted rate
0
1k
1.8k
2k
1.8k
1k
0
Use Your Eyes
Change of direction of Channel stream does
not coincide with time of local High / Low
HW Teignmouth, 6th August, is 14:19 hrs
Water
•
•
HW Dover, 6th August, is 19:55 hrs (5.5hrs later)
•
However tidal set in Lyme Bay is NE until 17:00(ish)
Eddies and Races
Solent Eddy
Tide-associated Hazards
•
Headlands and tidal races.
•
Overfalls
Confused seas occurring where fast-moving water meets (deep) slower-moving
water downtide, eg downtide of an island or headland.
•
Estuaries and bars.
•
Wind against tide, particularly at headlands.
•
Pinning
When a strong stream pins your kayak, broadside, against an obstruction, e.g. a
moored boat.
Allowing for Tidal Streams
•
Tidal streams, and kayaks, generally run parallel to coast. Then Tidal
Rates are simply added to / subtracted from boat speed.
•
Boat Speed = Speed Through the Water (STW). Not affected by tide.
•
Tidal streams affect Speed Over the Ground (SOG)
•
STW +/- Tidal Rate = SOG
•
Journey time reflects SOG.
Allowing for Tidal Streams (2)
•
•
•
•
•
Assume best club touring speed of 4.0 knots.
A 1 knot following tide will increase SOG to 5 knots and a 10 nm trip
will take 2 hours
A 1 knot foul tide will reduce SOG to 3 knots and the 10 mile trip will
take 3.3 hrs.
Add a F4 (15 knots) headwind and SOG could be further reduced to 2
knots. You probably won’t get there!
Tides are predictable; weather is less so.
Tidal Offsets and Ferry-gliding:
the tidal vector (1)
Tidal Offsets and
Ferry-gliding:
the tidal vector (2)
Use of Transits
Top Tips for paddling across tidal streams
•
Too much offset better than too little. Better to finish uptide of
destination.
•
Use a transit to monitor and adjust your ground track.
•
Paddle strongly.
•
Streams estimated >2 knots start with a 45o offset
•
•
•
Offsets >45o useless. Stick at 45o max and accept some down-tide
drift.
When tidal rate approaches your best boat speed (>3k ?) you will not
avoid some down-tide drift.
Beware of down-tide obstacles
If you have to paddle against a tide:
•
Seek shallow water and stay out of chanels. (Tide turns at edges
before mid-chanel)
•
Keep tight to the rocks.
•
Work the eddies
•
Avoid the middle 1/3rd of the 6-hour tide. (Stop for a cuppa)
•
Not a good idea if there is a head-wind as well!
•
A tail-wind will help
•
Beware headlands
Tidal Planning
•
•
•
•
•
•
If it’s an estuary put-in (eg Teignmouth) consider rates in the river and
harbour mouth.
Consider low tide mud at start / finish. Beware very low springs.
Research the main tidal streams and the current tidal range. Are they
big tides?
If headlands or tidal races are involved, pay particular attention to
tidal set and rate against time. The conditions at headlands may
dictate the planning of the entire trip.
Calculate speed and distances in consideration of tidal streams, and
also wind strength and direction.