Yachting and Boating World forums: Rule of twelths

This for those who may be unfamilier with the Rule of Twelths...

TIDES: Estimating tide rise and fall. The simplest rule of thumb for the guestimation of the height and speed of flow of the tide is the twelfths rule:

1 Hr. after low/hi water 1/12 of the tide height will rise/fall
2 Hr. after low/hi water 2/12 of the tide height will rise/fall
3 Hr. after low/hi water 3/12 of the tide height will rise/fall
4 Hr. after low/hi water 3/12 of the tide height will rise/fall
5 Hr. after low/hi water 2/12 of the tide height will rise/fall
6 Hr. after low/hi water 1/12 of the tide height will rise/fall

The speed of flow of the tide is approximately proportional to the amount of rise per hour, thus the fastest tide flows will occur at mid tide.

For greater detail consult a local chart and tidal atlas.

TME DIFFERENCES ON CARDIFF

Avonmouth +15 min
Barry - 15 min
Ilfracombe - 60 min
Milford Haven - 60 min
Minehead - 20 min
Newport +10 min
Swansea +45 min

INTERESTING FACTS: When during a year can we expect to find the largest tides? A day or two after the full or new moon nearest to the equinoxes. The spring equinox is usually the 21st March, and the autumn equinox, the 23rd September.

Some years have tides that are notably higher than other years. 1997 was a significant year, as will be the year 2015. For really favourable conditions - you will have to wait around until the year 3182. Even then, the tides may only be 1 or 2 cm higher than in 1997.

Post Extras