Tides and Currents in the Northwest
The following is taken from a handout KIX uses when teaching tides and currents.
Goals and Objectives – understand the reason why currents occur and how to handle them as a kayaker. Learn to predict tides and currents and to understand the hydrolics of local currents.
Tides – Vertical movement of water due to the rotation of the
earth and gravitational pull of the moon (and other factors
Current – The resulting horizontal movement of the water.
Ebb – Current which is flowing out (red arrows)
Flood – Current which is flowing in (green arrows)
Slack – The part in the middle during which there is no movement.
Maximum (or max) – The current is going the fastest. Usually seen
Rule of thirds, or 50/90 rule – One hour after maximum the current
is 90% the specified knots,
two hours later it is 50%.
Kayakers paddle at 3 knots when on an average tour.
In this area, current floods eastwardly into the Puget Sound region through the Straits of Juan de Fuca, and down the inside fo Vancouver Island. The ebb is the opposite! (See charts and whiteboard).
How tides and currents affect the kayaker:
Trip planning – easiest to go with the current
Hydrolics – learning to enter and exit eddies (eddies are areas behind rocks
and outcroppings where the flow is going the opposite way of the main current
– it is filling a vacuum).
(See whiteboard drawing of a rock in river). – learning to use large eddies
behind islands and friction near shore to your advantage
How to determine tides and currents:
Various books such as Captain Jack¹s Tide and Current Guides,
Captain Jack¹s Current Atlas, Island Canoe chart system, various sites on line such as NOAA.
Primary and secondary current stations.
Each are found in certain areas such as Rosario Strait, Deception Pass, Admiralty Inlet.
All of the above references list the primary stations and their readings
for ebb, flood, and slack. Kayakers are usually well away from the primary stations
and so need to calculate the difference between the primary station and the
secondary station where we may be. (Show and tell, practice).
Question for the group –
on a certain day should we paddle from Anacortes to Friday Harbor or the opposite?
Notice we have to read primary stations from both San Juan Channel and Rosario Strait.