"Capt. Scumbalino" wrote

| 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

Thanks for the explanation. So what's the difference between the rule of 12ths
and the rule of thirds. In the rule of thirds the first two hours it goes down 1/4
which is the same as your 3/12th. The second two hours it goes down 1/2 which is the
same as your 6/12th and the third two hours it goes down 1/4 which is the same as
your 3/12th. See I got it right in spite of myself.

Not a lubber, not a lubber, not a lubber... Yippee!

Cheers,
Ellen

Wrong.

Rule of 12's applies.

Ifyou want to break it down into 2 hours portions it works out like
this:
First two hours it goes down 1/4, middle two hours is 1/2, last twohours is
1/4.

"Ellen MacArthur" wrote in message
reenews.net...

"Joe" wrote
| Wrong...another lubber I see. The rule of thirds is fo tital stream
| flows .
|
| For height you use the rule of 12.

Don't EVER call this girl a lubber, you farmer! :-)

Rule of thirds works for tide height. In the first two hours it goes down
1/3 of its height.
In the next two hours it goes down 1/3 more and in the last two hours it
goes down the last
1/3. (I think.)

Cheers,
Ellen

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

"Bart Senior" .@. wrote in message ...
| Wrong.
|
| Rule of 12's applies.
|
| Ifyou want to break it down into 2 hours portions it works out like
| this:
| First two hours it goes down 1/4, middle two hours is 1/2, last twohours is
| 1/4.

I corrected myself when I answered 'farmer' Joe. :-0~ I wrote it down just
like you said after realizing how dumb the 1/3, 1/3, 1/3 thing looked. Duh!

Ask some more questions. I'll get the next one right. For sure. That one threw
me off for some reason.

Cheers,
Ellen

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

NO FAIR! I said rules of 12 first, gimme my point you Scurvey dog!

Joe




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

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

I'll give you 1/2 a point, because you did not explain how
it worked.

"Joe" wrote in message
oups.com...

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

NO FAIR! I said rules of 12 first, gimme my point you Scurvey dog!

Joe

Good point Jeff.

"Jeff" wrote

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.

Ellen MacArthur wrote:

Thanks for the explanation. So what's the difference between the
rule of 12ths and the rule of thirds. In the rule of thirds the first
two hours it goes down 1/4 which is the same as your 3/12th. The
second two hours it goes down 1/2 which is the same as your 6/12th
and the third two hours it goes down 1/4 which is the same as your
3/12th. See I got it right in spite of myself.

It's based on the pretty-much universal fact that the time for the tide to
change from high to low water, and vice-versa, is pretty close to six hours.
Since we humans deal with time in chunks of one hour, the question we ask
is: "how much does the tide change in one hour?". Since the smallest
fraction is one twelfth, just before and just after slack water, it's
natural to refer to the tidal change during other hours in terms of the same
denominator. One twelfth in the first hour leads us to express the change
during the second as two twelfths, etc.

Also, the larger the time slot, the greater the granularity. Imagine you're
waiting for the tide to rise enough to clear a sandbar. The rule of thirds
would have you waiting in chunks of two hours before you sail. The rule of
12ths would keep you at anchor for chunks of one hour. Of course, plot the
heights on a graph over time, and you can pinpoint your departure time
(rather, the time at which you can safely cross the sandbar) much more
finely.

Whilst your 'rule of thirds' (which, incidentally, isn't exclusive to
photography, but is a general principle used in many forms of visual art)
may be mathematically correct at its junctures, it doesn't fit with how
people think of time (ie, we think in days of 24 hours, not days of 12
bi-hours).


--
Capt Scumbalino

Bart Senior wrote:
I'll give you 1/2 a point, because you did not explain how
it worked.


I was busy givin the lubber more rope to hang herself.

If you do not give me a full point I will file a protest... and request
the ASA points commitee to rule on this matter.

Joe


"Joe" wrote in message
oups.com...

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

NO FAIR! I said rules of 12 first, gimme my point you Scurvey dog!

Joe