Metric system dumbs us down.

[El Pinguino]

Originally Posted by StuM

No haversines just involve arcs regardless of units. And nothing to do with subtracting big numbers. The Haversine function is just: haversin(θ) = sin²(θ/2) where θ is an angle in radians. Nothing to do with adding and subtracting large numbers,

The calculations are MUCH simpler if you use radians rather than degrees.
Note that all of the working is given in radians here: https://en.wikipedia.org/wiki/Haversine_formula


But of course - it's rollocks. I bet that even The Rain Man couldn't do that in his head

I have however written computer functions to calculate great circle distances and bearings which do exactly that ( in radians), so in a way, I have done those calculations in my head.

What we have above ( at Wiki ) is a fine example of theory which has no place in practical navigation as done by simple sailormen ever since Noah was a deck boy.... ok that's a bit of stretch... since the day Mrs Lecky's little boy got his first sailor suit.

Being a very clever chap, Stu, you will know what others may not. I shall carry on with some of basics for their benefit.

The beauty of the Haversine , which is half a versine, is that it remains 'positive' through the full 360 degrees, all other ratios change their signs at either 90 or 180 degrees.

While the 'Sine Formula' is the obvious choice if computerising your sight reduction the Haversine Formula comes into its own when working in longhand.

Longhand reduction using logs in the Haversine Formula goes thus -
Log Cos Dec + Log Cos Lat + Log Haversine LHA = Log Hav θ
Convert Log Hav θ to Natural Hav θ
Nat Hav θ + Nat Hav ( Lat ~ Dec ) = Nat Hav ZD
Convert Nat Hav ZD to degrees... job done.

The 'big numbers' of which I speak look something like this -

9.98211 + 9.99984 + 9.37772 = 9.35967 ( Convert ) 0.22890 + 0.01650 = 0.24540 = 59* 23'.5

If you use the sine formula you have to indulge in subtraction of those 'big numbers'.

Meanwhile its a nanosecond past Local Apparent Noon on the bridge of the s/s Ferret.

Captain Nastybastard 'OK 3/0 , whats the latitude?'

Freshly minted Third Mate ' Zero point three seven five six two four radians North, Sir'

SMACK

'ouch'

Capt NB 'Stupid boy........'

[StuM]

About the only justification for the nautical mile is that it is traditional and sailors love tradition.

For navigation purposes milliradians would be a much more appropriate distance since we are talking about spherical geometry.

(I milliradian is approximately 3.444 nautical miles)

[JPA Cate]

^^^^
Gotta agree with that, Stu. Young circumnavigatrix friend said to me, "The shortest distance between two points is a Great Circle route." Take that, Mr. Pythagoras!

Ann

[Jason Flare]

Originally Posted by StuM

About the only justification for the nautical mile is that it is traditional and sailors love tradition.

For navigation purposes milliradians would be a much more appropriate distance since we are talking about spherical geometry.

(I milliradian is approximately 3.444 nautical miles)

You seem to be OK with people doing whatever they want though, right?

[StuM]

Originally Posted by El Pinguino

What we have above ( at Wiki ) is a fine example of theory which has no place in practical navigation as done by simple sailormen ever since Noah was a deck boy

I'd just add that the vast majority of sailors today use exactly those formulae in their practical navigation. Every time they look at their chart plotter, they are using the result of those same calculations done in radians.

I'd like to remind you that the point of this digression into radians was NOT whether they should be used for manual calculations, but another posters assertion that they had no use at all.

[mikedefieslife]

Originally Posted by 44'cruisingcat

It's been noted the Romans used to drive on the left. So all of Europe drove on the left until Napoleon Bonaparte invaded them, and dictated that everyone must now drive on the right - just to be contrary. (He never got to Britain, so they stayed to the left.)

So for a lot of the world, not only the width of the road, but the side you drive on was dictated by a horse's arse.

It was because Napoleon was left-handed. Normally you'd cross people on your right, so you could draw your sword and engage if necessary. Being left-handed didn't work out too well for that.

[El Pinguino]

Originally Posted by StuM

I'd just add that the vast majority of sailors today use exactly those formulae in their practical navigation. Every time they look at their chart plotter, they are using the result of those same calculations done in radians.

I'd like to remind you that the point of this digression into radians was NOT whether they should be used for manual calculations, but another posters assertion that they had no use at all.

The only reason radians are used by computers is that computers are really rather stupid. They make no attempt to work in degrees being at their heart really rather primitive creatures... I discovered that in about when I was trying - in about 1971- to get some beast of a thing that even had its own cabin to reduce sights for me.

Seeing as I had to walk down 3 decks to where it lived it was far easier just to carry on doing sights in my head while waiting for the kettle to boil.....

[El Pinguino]

Originally Posted by Ann T. Cate

^^^^
Gotta agree with that, Stu. Young circumnavigatrix friend said to me, "The shortest distance between two points is a Great Circle route." Take that, Mr. Pythagoras!

Ann

Plane sailing over short distances is simple enough but a proper mercator sailing calculation, typically for distances over about 600 miles, is quite a complicated thing. If you really want to calculate the rhumb line 'course to steer' its easier to just work out the GC initial course and then apply a half convergency correction... tables for this can be found in your copy of Nories.

The same spherical trigonometry formula is used for both GCs and 'sights'.

[TrentePieds]

Oh, blimy - will it never end :-)!?

What's the point of our getting all bent outta shape and insisting on "metric" when it has no relevance to coastal cruising let alone serious seafaring? Porlier is 6 hours away, and I gotta get there in time to hit the slack. Porlier Pass is 15 minutes long on the slack, 5 minutes long on a fair tide and interminable on a foul tide. I don't care how many cables (or metres) it is.

I'm perfectly capable of laying TrentePieds dead in the water six inches off the bullrail on the hammerhead or a foot if that be my intent. But 6 millimetres, or even six centimetres? Forget it! Why would I even try?

Oh, and KVB: Note our little ship's name "TrentePieds", because that is what she is. Would it have sounded silly to call 'er "9.144" :-)? And don't let me get started on Old French Measures and the miseries wrought by the "Age of Reason" and the French Revolution!

Given our bottom contours where I sail, with the odd half-tide rock lurking about, I like to keep half a mile off the shore at all times, but 804.762 metres? Forget it! I know what halfamile looks like across the water. I don't give a hoot what 804.762 metres look like.

Like I said a coupla hunnert posts ago: I use an APPROPRIATE measurement system for what I want to do. I know what a cable length look like across the water. I don't give a hoot what a metre looks like. I loathe multi-digit numbers! I know that a fathom - wonder of wonders - is the precise distance twixt the tip of my middle finger on my right hand and the ditto on my left when I stretch my arms out. And my lead line tells me that it really appreciates that! What need have I for a newfangled depth sounder when TrentePieds only sticks down as far as I am tall, and my sounding lead is ever handy in my cockpit. What need have I for a compass rose marked in "new degrees" - 400 to the circle - when neither TrentePieds nor I can hold a course to an accuracy of half-a-point on a mariner's compass?

Now, when I'm building liggle choo-choo trains, a wonderful thing to be doing in the off-season, then I have REAL problems of mensuration! After all, in the scale I work (1:87.1 or 3.5mm = 1 FOOT!), the engine driver stands fully 825 thou tall. Thasright. we measure in "thous" (1/1,000") because while the (male) engine driver is 825 thou (21mm) tall, the lovely lady that bids you welcome aboard is all of 725 thou(18.5mm) tall, and careful differentiation is called for! "Thous" work better than mm.s because you can think and work in whole units unimpeded by decimal fractions. Again it is a matter of APPROPRIATENESS.

Sheets of plywood for building people-sized stuff ashore are 96 inches (= 8 feet) long, and so are sheets of what Yanks call "sheet rock", because 8 feet is the conventional finished floor to ceiling height in modern dwelling houses in NA, and the sheets can be bought in 10 foot lengths, (i.e. 3,048mm) because that is the conventional finished floor to ceiling height in commercial premises. Now, I can look at a room and know instantly how many sheets of "sheet rock" it requires, because the number is small and convenient. There is no way in Hades that I could now, or ever could have when I lived in Europe, go into a room and know instantly how many square millimetres of sheet rock I would need. That is because millimetres, despite the dimension stamped in millimetres on the corner of the sheet goods, are INAPPROPRIATE for the purpose at hand.

Now as for you, Ann ;-0)! - well of course you went back to the "imperial system". The foot plate of your sewing machine will have marks marked in inches. And your old Pffaf prolly did too, cos so many of them were sold this side of the pond. Berninas have "metric" markings, but who cares? A 1/4" seam is as close to a 5mm seam as "dammit" is to swearing, and unless your are like the little girl with a curl in the middle of 'er fore'ead, you can't control the run of the fabric to an accuracy of a millimtre anyway :-)! Tabling sails, whether you use a 2 inch tabling or a 5cm one makes zip difference. Ditto for a 4" v. a 10 cm tabling.

So when you get down to brass tacks the only thing that matters is that you use a convenient, APPROPRIATE unit of mensuration.

Peace :-)!

TrentePieds

[44'cruisingcat]

No chance of metrics ever dumbing that down...

[TrentePieds]

Bravo, Pinguino :-0)!!!

TrentePieds (ROFL)

[Kelkara]

Originally Posted by TrentePieds

I loathe multi-digit numbers!

To avoid multi-digit numbers you'll need a different unit every multiple of ten ... well, there's good news for you then!

[K_V_B]

Originally Posted by Kelkara

It's time we did away with minutes of arc too, and used decimal degrees, then if you really must we can then have a "nautical km" equal to 1/100 of a degree of latitude or 1111m ... or we could just print paper charts with a km scale down the side ...

If we go that way we should just use the 400 degree circle that surveyors use. That way a 100th of a degree comes out as 1 km. I'd be in favor of that.

However I can understand the expense of the change over. That is why the nautical mile got included in the SI system.

I can understand arguments based on familiarity and cost to stick with the imperial system. But those who believe that it is somehow "superior" are just grasping at straws...

..and push the metric button on our plotters.

Navigation on European inland waters is done in metric. Speed limits are advertised in km/h and distances are in km. Depths and heights are (of course) in meters.

Which is why plotters can indeed be set to metric...

Now imaging the confusion if we would have maps of the Oosterschelde would be metric one side of the Flood barrier, and imperial on the other side...

[K_V_B]

Originally Posted by TrentePieds

Oh, and KVB: Note our little ship's name "TrentePieds", because that is what she is. Would it have sounded silly to call 'er "9.144" :-)?

I doubt she's exactly 30 feet long.

And don't let me get started on Old French Measures and the miseries wrought by the "Age of Reason" and the French Revolution!

Actually France was one of the first countries to abolish the metric system... (And then reintroduce it after the rest of the continent had gone metric).

And the US was from the outset involved in the creation of the metric system. It is good to know a bit of history. The US could have been metric if the project had born fruit before the revolution.

Given our bottom contours where I sail, with the odd half-tide rock lurking about, I like to keep half a mile off the shore at all times, but 804.762 metres? Forget it! I know what halfamile looks like across the water. I don't give a hoot what 804.762 metres look like.

Why are you using statute miles at sea?

And do you actually navigate that accurately that staying 1 km from the coast would be impractical?

Like I said a coupla hunnert posts ago: I use an APPROPRIATE measurement system for what I want to do. I know what a cable length look like across the water. I don't give a hoot what a metre looks like.

I don't give a hoot what a cable length looks like. It is useless outside of navigation. Now knowing what a meter looks like is very usefull.

I loathe multi-digit numbers! I know that a fathom - wonder of wonders - is the precise distance twixt the tip of my middle finger on my right hand and the ditto on my left when I stretch my arms out.

First of all, I doubt it is.

And my lead line tells me that it really appreciates that! What need have I for a newfangled depth sounder when TrentePieds only sticks down as far as I am tall, and my sounding lead is ever handy in my cockpit. What need have I for a compass rose marked in "new degrees" - 400 to the circle - when neither TrentePieds nor I can hold a course to an accuracy of half-a-point on a mariner's compass?

But you do want to stay exactly half a statute (!) mile from the coast...

"Thous" work better than mm.s because you can think and work in whole units unimpeded by decimal fractions. Again it is a matter of APPROPRIATENESS.

What is the problem with decimal fractions? The nice thing about the metric system is that all you have to do to convert between units is move a decimal point. Something a second grader can do. Except if he's American apparently...

There is no way in Hades that I could now, or ever could have when I lived in Europe, go into a room and know instantly how many square millimetres of sheet rock I would need. That is because millimetres, despite the dimension stamped in millimetres on the corner of the sheet goods, are INAPPROPRIATE for the purpose at hand.

Actually I can.

Because when I see 8000 mm I see at the same time 8m and 80 dm and 800cm. At the same time. Instantaneously. Without having to think. Can you convert 7.369 Feet to Inches in the blink of an eye?

I can always use the appropriate measure, and do not need to get a calculator out.

Printing "Inapropriate" in capitals does not change that...

So if I see a drawing of a boat that uses m, and a drawing of a part that uses mm, I can see in a glance if the part will fit, or not. Can you do that if the boat's drawing is in feet, but the drawing of the part uses inches?

[JPA Cate]

KVB,
Oddly enough, if you have "the eye", you can do it in inches or metric measure. And if you don't, you haven't got it. I know a guy can see 25 mm. Now, to me, that's 10". He can also see 2.5, and I see that as 1", but slightly shy, 'cause I don't have the eye.

Trente Pieds,

Ah, well, how exact is 10 m.??????? ;-D

Ann