Reading a Chart in Metres

[AussieGeoff]

Originally Posted by Benz

Being unable to think in Metric (which is really one of the worst inventions of mankind)

Eh? I remember having similar thoughts when we went to metric. I was almost finished primary school and learned all the imperial units (which are slightly different to yours BTW).

Then we had to learn metric, so I had the benefit (though it didn't seem that way at the time) of learning both systems while still at school.

As someone else mentioned, the main issue is when you are converting between units. Having used both systems for many years, I can now say that I prefer metric for virtually everything. After dealing for years with 5,280 foot or 1,760 yard miles and 66 feet in a chain and 16oz in a pound and 22 hundreweight or 2,240 lbs in a ton, metric is something of a relief and I'm happy to work with it. I can convert easily between the major elements of metric and imperial but frankly there is very little need to convert these days. I mean, if you buy fuel by the litre, why do you need to know how many gallons that is?

A kilogram of water is one litre. A 1000 kilograms of anything is one metric tonne. One litre of water is also 1000 cubic centimetres. One kilometre is a thousand metres. For pretty much all your day to day needs, that covers it.

If you keep conversions to the base units, it makes it fairly easy.

Please note that my imperial measures are not all the same as yours, another curse of the imperial system, US and UK measures are not all the same, for instance your US gallons are smaller than our UK gallons, however a litre is a litre everywhere.

A kilogram is 2.24 pounds. Close enough to 2 and a 1/4.
A litre is almost exactly one US quart. 1.05xxxx, which is close enough for most things.
A metre is 3.28 feet or 39.37 inches, so it's about 3 and a 13 inches longer than a yard.
A kilometre is .621 of a statute mile.

The only one of these that are even slightly relevant to navigation is the relationship to the Nautical mile, ie one minute of latitude.
A nautical mile is 1852 metres.

It's up to you, but I'd say it was easier to remember a half dozen conversions than all the wierd imperial stuff and their (vague or non existent) relationships to each other.

All the metric measurements are related, so if you have a kilo weight, you can weigh a litre of water. If you have a metric ruler, you can measure a thousand cubic centimetre container which will get you a litre of water which weighs a kilogram. If you have a litre container, you can get a kilogram weight.

The only relationship in imperial weights and measures is the somewhat iffy one between pounds and pints, and the UK and US gallon are different volumes, so it's even more complex than it appears at first. And it won't much help you with units of length.

Sooner or later, the US will have to be dragged into the metric world, you are pretty much the last holdouts of an antiquated, complicated system that bears the same relationship to units of measure as the pounds shillings and pence we got rid of in favour of dollars and cents in 1966.
12 pence to the shilling, 20 shillings to the Pound, 21 shillings to the guinea, guess why we went to decimal? Same reason one day, despite all the protests of the hidebound, the US will have to catch up with the rest of the world and adopt the same system. I don't know how much damage or destruction has been caused by US persistence with this complicated and illogical system, but.... here's a glaring example.

Quote:
"NASA lost a 125 million Mars orbiter because a Lockheed Martin engineering team used English units of measurement while the agencys team used the more conventional metric system for a key spacecraft operation..."

Oops.

"...Lockheed Martin helped build, develop and operate the spacecraft for NASA. Its engineers provided navigation commands for Climate Orbiters thrusters in English units although NASA has been using the metric system predominantly since at least 1990."
End Quote.


My italics for emphasis. Note that NASA has been metric for over 20 years, because it's easier to work with the rest of the world that way, because that's what the rest of the world uses.



Imperial weights and measures need to go the way of the dinosaur.


The defence rests.


Ok, now I've probably started something equivalent to the Ferro v GRP wars and the Multihull v Monohull wars. Ce la guerre.



AussieGeoff

[bewitched]

Originally Posted by Benz

Being unable to think in Metric (which is really one of the worst inventions of mankind).

Yeah, the imperial system was much easier. . You knew that there were
12 inches in a foot
3 feet in a yard
22 yards in a chain
10 chains in a furlong
8 furlongs in a mile
And a mile was 1760 yards or 5280 feet.

Ahh... But that was a land mile and those were land measurements. Regarding the sea there were
6 feet in a fathom
15 fathoms in a cable
There wasn't a relationship between a fathom and the next one ... A cable
But there was 608 feet in a cable and so
10 cables in a nautical mile.
Which was 6080feet
Which is the only measurement that makes any sense as in is the same length as one minute of arc of latitude at the equator....well give or take a few feet.

But if say you wanted to measure cloth, or area, or volume, or pressure, or energy, or....

Well, then it got a bit tricky.

[HappySeagull]

ALL systems of measure are arbitrary.
one cubic "centimetre" = 1 "gram" of water...but one centimetre is derived from one minute of arc on Earth....so it's from a base360 system...
Now,stir in Clocks per 12 hours...ie:WHAT is Metric time,tell me?

There's so much baggage in "measurement" that anyone that "rests their case" per the merits of their favourite has really just collapsed from exhaustion.

Origin of the Metric System

[AussieGeoff]

Originally Posted by HappySeagull

Now,stir in Clocks per 12 hours...ie:WHAT is Metric time,tell me?

Probably the Swatch beat. That was reinventing the wheel without any good reason. For some reason, time is the one system that is the same world wide and everyone learns the same system, which is simple enough that it doesn't need changing. Once you get below seconds, it becomes metric, ie milliseconds, microseconds, nanoseconds... so...

One could also argue that we should navigate using mils instead of degrees, but that's an argument for another time and place.

Ultimately, if systems change, it's because there is a perceived benefit, in the case of metric v imperial, whatever your own preferences (and I still have a more 'instinctive' understanding of miles per gallon that litres per 100km.) it was to migrate to a system that is simpler to understand as all units are multiples of the base units, gram, litre, metre. This is most assuredly not the case with imperial measures.

AussieGeoff

[Keithgdgp]

You are definately correct. The smaller number is a decimal of a meter. A meter being 39.34 inches.

Regards,
Keith DG

[bewitched]

Originally Posted by HappySeagull

ALL systems of measure are arbitrary.

They did try very hard for that not to be the case.

Unfortunately, they measured north south instead of around the equator and so time was forever excluded from the metric system. (Who wants a 40hour day!!)

Come on Myanmar, Liberia and America. Join the rest of the world. Adopt SI units today!!!!

[Kettlewell]

A lot of depthfinders let you switch to metric units--that's what I do when I'm in an area with metric charts. Makes life easier.

[David_Old_Jersey]

Originally Posted by Benz

Being unable to think in Metric (which is really one of the worst inventions of mankind)

I grew up through the change over to Metric, fortunately I was young enough so school only taught me the one system ....but nonetheless am comfortable with both systems. Indeed sometimes my measurements include both!................A month or so back I ordered 15 metres of wood batten. Should have been 15 feet (i'd measured the width in cm's ).

But I am thankful for never having needed to learn the old money - a thruppeny bit = 1/2 a groat. But to be fair, a thruppeny bit would go a long way back then

[nigel1]

Quite like a nice pair of thruppeny bits

[HappySeagull]

Body Parts-that's the way to go....a cubit(elbow to fingertip),an inch(a finger joint) an eyelash,a hair,a palm,a foot(great to measure with),a fathom(-enough to drown in)-these will never be replaced

[sailingmonica]

Originally Posted by Benz

Being unable to think in Metric (which is really one of the worst inventions of mankind), I have copied a page from Bowditch that converts meters to Sensible, laminated it, and posted it above the nav station. It takes an extra step to glance at the chart and convert, but it's better than trying to navigate with unusable information.

Metric: 1 metre=10 decimetres(betcha you haven't heard this one)=100 centimetres=1,000 milimetres. You're saying it's complicated.

Imperial: 1 yard=3 feet=36 inches=288 eights of an inch=576 sixteens of an inch. Now THAT is really simple!

[jackdale]

Originally Posted by HappySeagull

ALL systems of measure are arbitrary.
one cubic "centimetre" = 1 "gram" of water...but one centimetre is derived from one minute of arc on Earth....so it's from a base360 system...
Now,stir in Clocks per 12 hours...ie:WHAT is Metric time,tell me?

There's so much baggage in "measurement" that anyone that "rests their case" per the merits of their favourite has really just collapsed from exhaustion.

Origin of the Metric System

1 minute of arc = 1 nautical mile (from the site you posted)

1/10,000,000 0f the distance from the equator to the pole was a meter. Since 1983, it is defined as the length of the path travelled by light in vacuum in 1⁄299,792,458 of a second.

There is SI conventions for dates and time - largest to smallest.

[Pete7]

So are people really still using charts in feet then Gosh how quaint, just like in the days of Lord Nelson.

Pete

[Connemara]

Originally Posted by sailingmonica

.... one's draft, which is generally around 2 metres ....

Really?

Someone sawed a bunch off my keel then.


Connemara

[HappySeagull]

Originally Posted by jackdale

1 minute of arc = 1 nautical mile (from the site you posted)

1/10,000,000 0f the distance from the equator to the pole was a meter. Since 1983, it is defined as the length of the path travelled by light in vacuum in 1⁄299,792,458 of a second.

There is SI conventions for dates and time - largest to smallest.

IF it'd ALSO been agreed on to 200 or 2000 "degrees" in a circle,...to match the 20,000,000 metre circumference...unfortunately,the British and the French were not getting along at the time and we are still paying for it with two sets of socket wrenches ....maybe they should try again.