Convenience of the metric system
A example where you see the advantage of the SI system.
Lewmars windlasses V1 have according to the datasheet: The motor has a max power of 700 W. Working load 113 kg. To lift 1 kg you need a force of 9.8 N or about 10 N. The force the windlass pulls with is then 1130 N. Maximum chain speed is 19 m/min. That corresponds with 0.317 m/s. The power on the gypsy is then 1130 N * 0.317 m/s = 358 Nm/s = 358 W The efficiency of the windlass is then 358 W / 700 W = 51%. That’s not much but its what you can expect for a worm gear. I remember that there is 12 inch on 1 foot, but I don’t see the logic in that. I never remember how many yards there is on one mile, and even less the logic in that. There is 1000 m (meter) on 1 km (kilometre) is very logic since kilo means thousand. It’s the same that there is 1000 mm (millimetres) on 1 m (meter), because milli means thousandth. A cube with a side length of 0.1 m (meter) have a volyme of 1.0 l (liter). 1.0 l (liter) of watter have a wight og 1.0 kg (kilogram). Approximate conversion between the two systems 1 m (meter) is 40 inches (39.37). 1.6% wrong. 1 m (meter) is 3 foot (3.281). 8.6% wrong. 4 l (liter) is 1 gallon (1.057). 5.7% wrong. 1 kg (kilogram) is 2 pound (2.205). 10.3% wrong. 1 m/s (meter per second) is 2 mph (2,237). 11.8% wrong. 1 m/s (meter per second) is 2 knots (1.944). 2.8% wrong. 
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Uuuuhh !! Ookay. :smile:

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"1.0 l (liter) of watter have a wight og 1.0 kg (kilogram)."
You must have a metric spellchecker.:biggrin: The imperial system was not based on logic, so it needed none to understand it. You just had to learn the tables.:thumb: Even today if you tell me somebodies height and weight in metric I would have no idea if he was a fat midget or a skinny giant. I learnt the imperial system and it still works for me because I can judge something in inches/feet/yards by eye and do not even try to convert. It is simply what you feel most comfortable with really, nothing to do with being better or worse than the other.:wink: Coops. 
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Oh, Coops, No, no, no! :banghead:
Metric makes the most sense....except it is largely opaque if you learned Imperial as a child. The problem is getting all those Yanks to change what they do. We came close to metrification, a while back, but as far as I can see, little progress has been made. And we get by okay, as you suggest, because you learn it when you're little and it becomes part of your whole language acquisition skills and it's ruddy well stuck in there! :smile: Cheers, Ann 
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The problem with the metric system is based on 10. Why 10, what a stupid number to base a number system on, what is that? Because we have 10 fingers!!! Dumb.

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In my spares kit I have BSF,BSW,AF and Metric mm capscrews in 1.25, 1.50, and 1.75 thread pitches. Makes it interesting. On early Mitsubishi cars, you could find all of them on the same vehicle.

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In the UK they "almost" converted to Metric, the problem now for example Copper Tube, you can buy Metric and Imperial. Although close they don't fit together.
:smile:They also still drive on the wrong site of the road... 
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My only problem with the metric system is it needs something between a meter and a Cm. If you say to me something is 2 ft long I get it. If you say 60cm... My brain has to convert it... If it made sense that things must be described in multiples of ten... well then wouldnt it make sense to only build things in exact multiples of ten?
How about time? should we break it into tens? How about the naturally occurring number Pi? We'd better round that down to 3.000.. :>) 
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May I suggest some better rules of thumb. Not 1m = 3', which is way off, but 3m = 10 feet  which is pretty close, and plenty close enough for a rule of thumb  as soon as you need more precision, just go to 1" = 25.4mm and take it from there. Not 1kg = 2 pounds, but 1kg = 2.2 pounds, which is exact. Not 1 m/s = 2 mph, but 1 m/s = 2 knots. And just memorize: 1 statute mile = 1.62 km, so 100 km/h = 62 mph and so forth. 1 inch = 2.54 cm With just those bits, you shouldn't have any problem with the metric system. Now, as to 12 inches in a foot  what is so inevitable about Base 10? 12 is a much better subdivision than 10  can be divided more ways. Actually, Base 12 is really powerful, and there is an actual movement to replace Base 10 with it, see: Why We Should Switch To A Base12 Counting System 
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My car gets 40 rods to the hogshead and that's the way I likes it!!!

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Both require a functioning memory :thumb:
The metric system quickly becomes unusable if one forgets value of the multiplier of the micro, milli, deci, centi, kilo, mega, giga, hecto; and that is only the common ones, not the esoteric ones. I see many metric trained people unable to quickly comprehend even simple measurements when say given in millimetres but they were expecting centimetres. When working in fractions, 12 is a far better base than 10. Metric is certainly more arithmetic friendly. Having said that, I really do prefer to be "ambidextrous" and use what is most simple for the job. Personally I will use thousandths of an inch rather than microns; hectopascals instead of inches of Hg.; PSI instead of Bar; miles or kilometres depending on circumstance. The list is long but I'm sure you get the drift. 
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Stupid system that only Englishman and Americans understand. BTW. why you accept the Metrical system for Currency??? The old English system made more sence for me 
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In land surveying, a Chain is both a measurement, and the tool to determine it. It is 22 yards, the length of a Cricket Pitch wicket. ther ya go.

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English units are generally intuitive as they are based on humans.
 Inch = length from tip of thumb to first joint  Hand and Foot = obvious.  Yard = tip of nose to outstretched hand.  Mile = 1000 paces  Cup = A typical amount a human will drink. Metric is based on the properties of water and the distance from the equator to the pole.  Meter = 1/10,000,000th of the distance from the equator to the pole  Liter = volume of 1/100,000,000th of the distance from the equator to the pole cubed  Gram = mass of water contained in 1/10,000,000,000th of the distance from the equator to the pole cubed. Metric is convenient for hand calculations but the mass of 1/10,000,000 of the distance from the equator to the pole cubed...isn't very intuitive. Nor is a height of 1.6/10,000,000th of the distance from the equator to the pole very intuitive. 
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It's obvious that Lars is trolling. But I find it amusing that he would calculate how "wrong" in percentages, the Sensible system is compared to metric. We could easily say that metric is wrong by those percentages: why isn't a cm an inch long? would have made better sense. But where he's really wrong is in trying to convertif everyone did their measuring in inches and feet and didn't bother trying to convert that to metrical, there would be no need to approximate between the two.

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As a Canadian who was in school during our transition to metric, I can reasonably move between the two systems with some ease. There is no doubt Metric is far easier to work with when making any sort of calculation beyond the most basic.
For me, some measurements for me are more natural in Imperial (person height or keel lengths), and some are clearer to me in Metric (0 degrees Celsius vs 32 Fahrenheit). A cm is as useful as an inch, a meter is as good as a yard, and a litre works for quart and pints. Millimetres are far better that fractions of inches for machine bits, and km are more obvious to me than (statute) miles. However, I still think more in pounds when it comes to human and boat weights. Neither system is inherently more "intuitive" than the other. It depends on what you've been brought up with. But there's no way you can argue Imperial is easier to work with for complex measurements or calculations than Metric. Its no accident that even in the USA, scientists have long operated in Metric. It's only a matter of time before Liberia, Myanmar and that other holdout country will join the rest of the modern world :wink:. 
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From Wiki: While most countries replaced the mile with the kilometre when switching to the International System of Units, the international mile continues to be used in some countries such as Liberia, Myanmar,[3] the United Kingdom[4] and the United States.[5] It is furthermore used in a number of countries with vastly less than a million inhabitants, most of which are US or UK territories, or have close historical ties with the US or UK: Am. Samoa,[6] Bahamas,[7] Belize,[8] British Virgin Islands,[9] Cayman Islands,[10] Dominica,[10] Falkland Islands,[11] Grenada,[12] Guam,[13] The N. Mariana Islands,[14] Samoa,[15] St. Lucia,[16] St. Vincent & The Grenadines,[17] St. Helena,[18] St. Kitts & Nevis,[19] the Turks & Caicos Islands,[20] and the U.S. Virgin Islands.[21] The mile is even encountered in Canada, though this is predominantly in rail transport and horse racing, as the roadways have been metricated since 1977.[ 
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Add this. Celsius means 0 degrees is the freezing temp if h2o. 100 degrees is when it gets boiling. Simple.

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Canada converted to the metric system in the mid 70s, 35 years ago. My kids learned it in school.
To this day, imperial units are still used. The rural land grid is 1 mile x 2 miles, that won't change. Houses were built with 2x4 or 2x6 studs, that won't change. Plywood is 4'x8', and that won't change. A baby weights 6 pounds 4 ounces, and if you tell the mother that her child weighs 2835 grams no one will know what the heck that means. Same for height. The reality is that although the metric system makes all sorts of sense, for those countries that are not on it or for many years were not on it, standards evolved that can not change, such as how buildings were built. Even after 35 years of metrification, even after the children learned only metric in school, after all that, the imperial measurement is still referred to. In stores, legally they have to sell by the kilogram, yet all prices are marked in pound weight. That is the market. 
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Might think the diameter of the solid fuel rocket boosters of the space shuttle would be an arbitrary dimension best suited for launching into space. But no, they are really sized to fit through rail road tunnels between Utah where there were made and Florida where the space shuttle was launched.
The rail road tunnels in the US were of coarse based on the dimensions of the first railways which were developed in England. These first railways were of coarse built by the carriage makers whose craft lent itself well to this new mode of transport. The carriage makers of course had been sizing their carriages to work on the roads that existed in England prior to the railways. The dimension for the ruts in the roads from which the carriage makers built the new railways was of coarse based on the carriages the Romans had used when the roads were first made. So basically a key design constraint for the space shuttle was the wheel width of a Roman cart. 
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Some roman bureaucrat determined the original with of a cart based on the width of two horses asses. So when all is done and said the size of the space shuttle rocket boosters are based on the width of a horse's ass. 
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Eventually, the powers that be came to their senses. 
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Americans claim to use the Imperial Measurement System, rather than the Metric one.
Yeah right, they all know what 9mm is though. 
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In my former career in the underwater acoustics business I had to constantly work with scientists, commercial operators, and military from one NATO navy or another. I don't know the point at which I started preferring metric units of measurement, but it did happen. Even today, when I need to buy a new tape measure, for example, I will choose one that has both inches/feet and also millimeters on it. I'm a long time woodworker, and have built a lot of fairly complex furniture over the years. Right now I'm cutting some relacement mahogany corner mouldings for the boat. I much, much prefer working with millimeters for measuring and cutting. Trying to measure and divide 11/64's or adding a series of lengths together can be really problematic with the "old" US system.
I also plan, someday, to renumber my sets of wrenches and to engrave a new designation on them. I have found that working on my own cars, trucks, motorcycles, airplanes, and boats that I definitely need to have two complete sets of imperial and metric wrenches, sockets, allen keys, etc. And over the years, I find that I've learned to think of them in combined terms. The slight differences in similar sized wrenches, for example, can be extremely useful. Especially when working on old or corroded machinery. Take the example of a corroded 1/2" nut that is diminished in mass by rust and wear. It's not uncommon to find that a 1/2" wrench will slip and round the remaining edges of a worn 1/2" nut. Or bolt head. BUT if you "drop down one size" to a metric 12 mm, often you can get a snug fit. Conversely, sometimes I might need to go up a half size due to rust scale or maybe a coating. I have wondered why someone doesn't just combine the two sets of wrenches, and renumber them according to their increasing size. And give them the appropriate numbers. So if a 5/16" socket is too loose on a nut, The next size down would actually be metric and a 7 mm. In my perfect wrench set, that might mean putting down the # 6 and picking up a #5. With #6 being 5/16" and #5 being 7mm. THEN I could quit going back and forth from one tool box to the other. Combine them ALL and relabel them according to increasing size. And the same thing could be done in other areas. No reason you shouldn't be able to choose based upon increasing unit of measure, and still have the "stops" in the assortment to accomodate standard item sizes or values from years ago. No reason a 12 oz soda or beer couldn't be still be the same size physically, to fit all those six pack coolers. No reason that allen head screws couldn't be graduated the same way, with metric and imperial intermixed according to size. 
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Sailing is a simple sport and in its pure form does not call for rarefied levels of calculating prowess.
I grew up in metrics but I fail to see any convenience of this particular system. I am happy with miles and degrees and fathoms. I prefer a gallon over a liter too. Especially to measure our rhum tankage. b. 
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I would prefer my polar tables to compute furlongs per fortnight. Who only sails for one hour at a time anyway?

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having preferences is fine, to a point. and moving that point right or left to divide or multiply by ten is easier with metric.
And who really cares how much volume the beer stein or rhum glass holds? You will still always reach for 'the big one'. 
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Before that it was the length of a bar kept somewhere in Paris. Before that they indeed took 1/10000000 of the distance from the equator to the pole, because that ended up a good size, about the length of a pace... Incidentally the nautical mile is defined in a similar way, as the length of one arc minute measured on the equator. This gives all kinds of advantages when doing astronomical navigation. For the same reason surveyors in metric countries will measure angles in "gon", of which 400 go in a circle... 
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Some interesting conversions:
1 million microphones = 1 megaphone 1 million bicycles = 2 megacycles 2000 mockingbirds = 2 kilomockingbirds 10 cards = 1 decacards (or is it 52 cards = 1 deckacards?) 1/2 lavatory = 1 demijohn 1 millionth of a fish = 1 microfiche 453.6 graham crackers = 1 pound cake 10 rations = 1 decoration 10 millipedes = 1 centipede 31/3 tridents = 1 decadent 10 monologs = 5 dialogues 2 monograms = 1 diagram 8 nickles = 2 paradigms 2 wharves = 1 paradox 
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And the loading gauge is another different matter. That is a lot larger then the one used in the UK... (In the US everything is larger after all...) 
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At some point I did the mental math of the use converting to the metric system in terms of road signage. There are about 4 million miles of roads in the US. England OTOH has about 250,000 miles. Not a small undertaking to convert. 
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I was talking to my hunting guide friend about bullet size a while back. I had the millimeters figured out but never thought about the caliber size. I asked him if it was based on something and he said it was totally random measurement. It took me less than a minute to find out it was based on 100ths of an inch thanks to Mr. Google. So here we have a hunting guide that has probably shot 10s of thousands of bullets that has no clue what a bullet size comes from. Think about that! 
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And let's not forget the metric unit every sailor should know  the millihelen.

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