The rule of twelfth's

[johnalison]

Ah, metric eh?

More of an Imperial sort of bloke, me.

So you're a fathoms man eh?

I'm ashamed to say we used a fathoms chart this summer.

 

[FullCircle]

I have several cancelled planning charts including a gnomic chart in fathoms of the North Sea.

I also understand ft/lbs ft/lamberts, the many variations on the ounce.


I always felt that our inscrutable system of measurement kept Johnny Foreigner confused for centuries.

 

[Sixpence]

Not surprisingly for my age, I am happy looking at fractions but find a percentage hard to visualise, depths are viewed as metres on the display but converted to English when I want an idea how much water is under me

 

[pennycar9]

For what it is worth, my rule of twelths is about a foot long and is divided up into twelve inches. I use it to measure stuff. I have been known to quote that ' I have 12" but I don't use it, as a rule'

 

[peterb]

Imperial?

You can have fun with "Imperial" units. I used to be on several European Standard committees. On one working group the UK delegation (with straight faces) started talking about guineas per furlong fortnight. At least we knew we were talking nonsense; the others didn't!

 

[peterb]

If I understand this sort of properly, if I'm on open water at high tide, with an intended passage plan taking me in a straight line from point 'A' to point 'B' and estimated at twelve hours crossing time, then ignoring any other factor, if I maintain course for the duration of the crossing, then any tidal flow affect will be cancelled out ?

Just one word of warning. The tidal stream doesn't always have a simple relationship with the tidal height. Most people seem to assume that the tidal stream flows one way until high water, then in the other direction until low water, and so on. It may not be that simple.

If you want a simple example, imagine a big lake joined to the sea by a narrow channel, which so restricts the flow that the level in the lake hardly changes at all. Now think about the difference in level between the sea and the lake. You'll get the greatest difference at high water and low water, so that's when the flow in the channel will be at its greatest. Maximum flow at low and high water, minimum flow at mid tide, when the level of the sea is changing most quickly. I know it's an extreme example, but there are many places that show the effect to a smaller extent.