Well, actually, these are the places where one would be very interested in how quickly the
current ramps up. They differ from most locations in that they are driven by two bodies
of water that are of different heights, as opposed to one body of water draining out.
True slack at thesse places hardly exists - you might get 20 minutes of low current.

However, places like Boston, though not as dramatic as Wood's Hole, get to half strength
in a little over an hour, so I don't know how the rule of 12ths would be applied.
http://www.mobilegeographics.com:81/locations/678.html

Marc wrote:
Agreed, thus the use of "sometimes". CCC, HG, and WH are definately
not places for rules of thumb.

On Tue, 2 Sep 2003 12:18:49 -0400, "Jeff Morris"
jeffmo@NoSpam-sv-lokiDOTcom wrote:

It doesn't work too well for currents. In places like the Cape Cod
Canal, Hell Gate, and Wood's Hole the current ramps up to over half
strength in the first hour.

Marc wrote:
ratio of tidal rise over time.

Rule of Twelfths
Shape assumed to be sinusoidal
Rise in 1/12ths
1 in first hour
2 in second
3 in third
3 in fourth
2 in fifth
1 in sixth

sometimes used as a rule of thumb for tidal current as well




On Tue, 2 Sep 2003 11:21:19 -0400, "Simple Simon"
wrote:

Since Booby is too ignorant to answer the following question,
I'll throw it out to the group as a whole.

What is the rule of 12ths and how would you use it?


S.Simon - a Captain who's serious about sailing