Kayak Fisherman Ireland

Rule of Twelfths

One thing that has a huge bearing on how far kayaks paddle is how fast or strong the tidal flow they will be traveling with or against is. I grew up on the east coast of Ireland and this is where I learned to fish from a kayak. We have strong tidal flows here and it was imperative that I learned how to understand them. Any distance that is covered on an outward leg of a journey has to be repeated to get back to your launch point, particularly important if you travel up or down tide but just as relevant if you travel straight out to sea. Bearing this in mind it would be good practice to familiarise yourself with the ‘Rule of Twelfths’.

pie chart illustrates the proportion of each hour of tidal flow according to the rule of twelfthsWell known to surfers, windsurfers and other water users, the Rule of Twelfths is a method used to understand when the peak flows of any tidal cycle will occur. In areas where tides can be strong it is a useful rule to enable the kayaker to figure out when the best and easier times to paddle will be. Ideally you want to paddle with the tide when it is at its strongest and against the flow when it is at its weakest. Paddling against a strong flow is exhausting work and although you will generally make some headway, a minute’s breather can see you swept back to where you started. You can always travel down tide with the flow, wait for the slack and then paddle back with the turned tide but sometimes life and time restrictions do not allow for launching in perfect synchronisation with this pattern which is where the Rule of Twelfths comes into play.

Taking low tide to high tide as a starting point we have a period of slack water to begin with. The low to high tidal run will last approximately six hours. If we take the full tidal flow as a fraction, twelve twelfths, we can divide this fraction against the tidal flood thusly; the first hour of flow will be one twelfth of the entire flow’s power. The second hour equates to two twelfths while the third and fourth hours will equal three twelfths each. The fifth hour will see the flow starting to weaken back down to two twelfths, the final hour drops back to one twelfth to eventually bring us to the next slack period as the tide turns once more. Once turned and starting to ebb, the same logic is applied to a dropping tide.

get it wrong and it feels like paddling upstream on a river like this

What this all means is that for a six hour tidal cycle the flow will be at its weakest for the first and last hours, the hour closest to slack water at each end of the tide. These are going to be the easiest times for paddling and will require the least amount of energy and effort to travel against the flow. The third and fourth hours will have the strongest tidal flows. This is the ideal time to use the tide to push you along to where you want to get to. It is also the worst time to be paddling against the tide and depending on its strength it will cost you a lot of time and effort to paddle against, even to cover just a short distance.

Strengths and flows will depend on your locality and whether the tide is running as a spring, neap or in between. The flow ratio as seen in the Rule of Twelfths will still apply. Understanding when the peak tidal flows will occur will enable the angler to assess when they think the best time for paddling and the best time to anchor or stay off the water will be. I learned the hard way on one of my earlier paddling adventures. A leisurely twenty five minute paddle turned into an hour and a half’s struggle on the way back!

By Gary Robinson

Article seen in Sea Angler
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