While the Rule of 12ths is a very handy tool for estimating the tide
height at any point in the cycle, I would be very careful of using to
extrapolate total range from one hour's observation. For instance, if
your observation were off by one inch, then you might mis-estimate the
full range by a foot.

On a related topic, sometimes people will claim that the Rule of 12ths
also applies to current estimation. This is generally not true.
The strength of the current through the cycle is highly dependent on
the local geography. In particular, the strong currents that are
generated by tidal differences on connected bodies of water (Hell
Gate, Cape Cod Canal, etc.) ramp up very quickly and their chart is
more of a square wave, than a sine.



Bart Senior wrote:
The point I wanted to make you covered. 1 point to Capt
Scumbalino.

If the range of tide is 8 feet, the first hour is 8".

For a six hour cycle, Multiply by twelve to get inches and
divide by 12 to get 1/12.

It is easier to simply check the range of tide and change
the units to inches.


"Capt. Scumbalino" wrote

Ellen MacArthur wrote:

OK! You got me. Your not a farmer. (blush, I guess I blew my sailing
test debut)
For someone that moans about lack of sailing content in what is widely
seen
as a virtual yacht club bar (where the patrons also talk about stuff other
than sailing), you have a lot to yet contribute.

The clue is in the 12ths part...

hour change as a fraction of tidal range
1 1/12
2 2/12
3 3/12
4 3/12
5 2/12
6 1/12

Say the tide drops 5" over the first hour. Since you know that that 5" is
one twelfth of the total range, you can calculate that the tide will have
dropped 5"x12 = 60" = 5 feet when it gets to low water. Of course, 5' is a
girly tidal range. Here, it's a proper, manly 5 metres (or more).


--
Capt Scumbalino