I can easily visualize distances in both units (just try not to involve furlongs here, ok?) But it's temperatures that get to me... I can't quickly estimate equivalent values between Celsius and Fahrenheit. And with all due respect to Mr Fahrenheit, but I think he did a humongous blunder when he involved the behavior of two different substances to define his scale.

Before we get too caught up in decrying his efforts as a blunder, let's keep in mind that we are looking in hindsight. At the time he did his work, early 1700's, the goal was usually to define units that people could reasonably reproduce with reasonable effort and that spanned the useful range of experience for most people. I've often heard -- but don't know if it is true -- that his goal was to define a reproducible temperature scale that approximated the range of outdoor temperatures encountered by most people (over which geographical area I have no idea). So he was looking for something that most people could reproduce at each end of that spectrum and decided on brine and human core temperature. The level of reproducibility didn't need to be too rigorous since the goal was often to aid in commerce and any often any level of reproducibility was better than the status quo.

 

Thanks you reminded me that our sailors also use knots per hour.

No such thing as knots per hour (actually, that's not strictly true, 1 kt/hr would be an acceleration of about 15 microgee if I did the math right).

One knot is defined as one nautical mile per hour.

 

Thanks you reminded me that our sailors also use knots per hour.

"per hour" is redundant when using Knots.
At least that is the way I 'Fathom' it.
Max.

 

I wander if that's still going to be the case 100 years from now.

Could be. It's real hard to make changes to deeply entrenched systems, particularly if they are highly distributed, wide spread, and have to deal lots of legacy components.

That's what the folks that keep trying to push the U.S. change to metric (a move which I support, by the way) keep running into. With both a large population and a highly developed industrial and commercial infrastructure, such a change is disruptive on a scale that dwarfs what most other countries experienced. It's not impossible and I believe it will happen, but it is going to be a very long process. In the end it will be more costly then it would have been had it been forced at a quicker pace, but that cost and pain will be spread out over a much longer time making it less disruptive and palatable overall.

 

And bridges maximum allowable vehicle heights .

Like Max Head Room for e.g.
Max.

 

Hello,

Living in Holland I always have used the metric system.
You will have the inch,pound and gallon, we have meter, kilo and liter.

Bertus

 

"per hour" is redundant when using Knots.
At least that is the way I 'Fathom' it.
Max.

My bad. Not used to using knots as a measurement for anything in my life.

 

I wander if that's still going to be the case 100 years from now.

The use of knots, or more specifically the nautical mile, actually makes a lot of sense for long distance, particularly nautical, transportation. The original definition was basically a change of one minute of latitude (or one minute of longitude at the equator).

One of the reasons is that large area maps have real problems depicting 3D surfaces on a 2D representation and linear scales are particularly problematic. But such charts were made with the idea of using chart dividers for navigation and so tying the distance measure directly to the latitude measure makes distance computations much easier.

With today's tools, this benefit is largely gone, however, so there is less justifiable resistance to making the switch.

 

The use of knots, or more specifically the nautical mile, actually makes a lot of sense for long distance, particularly nautical, transportation. .

Originally devised as a means of reckoning speed/distance, by knots in a rope fed overboard.
The term still sticks today.
Max.

 

Originally devised as a means of reckoning speed/distance, by knots in a rope fed overboard.
The term still sticks today.
Max.

As this one does too:

Traditional terms for soundings are a source for common expressions in the English language, notably "deep six" (a sounding of 6 fathoms). On the Mississippi River in the 1850s, the leadsmen also used old-fashioned words for some of the numbers; for example instead of "two" they would say "twain". Thus when the depth was two fathoms, they would call "by the mark twain!". The American writer Mark Twain, a former river pilot, likely took his pen name from this cry. The term lives on in today's world in echo sounding, the technique of using sonar to measure depth.

http://en.wikipedia.org/wiki/Depth_sounding#Terminology

 

Originally devised as a means of reckoning speed/distance, by knots in a rope fed overboard.
The term still sticks today.
Max.

To some degree this is a chicken/egg discussion, but I think we are in pretty close agreement. The knots were placed at intervals such that a thirty second count would equate the number of knots to the number of nautical miles per hour. I'm not aware of "knots" being used to judge speed prior to that, but it is certainly possible. While the chip log, which worked on this same basic principle, predates the adoption of the nautical mile (though not by much), as far as I know the use of knots in the line (as opposed to just measuring the line once it was reeled back aboard) only started after the adoption of the nautical mile and specifically to calibrate the chip log to nautical mile per hour. The use of the term "knots" almost certainly derives from this adaptation.

Interestingly, but probably not too surprisingly, the distance between knots was not set so as to give a direct measure of knots in a 30-second interval, but rather the knots were set at a distance of 8 fathoms and the hour glasses used for timing adjusted to 28 seconds instead. Since 1 nm is 6076 feet (approximately) and 1 fathom is 6 feet, at 1 nm/hr it takes 28.4 seconds to play out 8 fathoms of line. I don't know if the discrepancy was just to try to make the timing glass to a round number of seconds or if it actually reflected an attempt to compensate for some error source. At first I thought that it might be to compensate for the fact that the drogue (the "log") won't actually stay still in the water but will actually move in the direction of the ship. But that would require the use of a longer time interval to play out the same amount of line.

My guess is that the decision to adjust the watch to match a "round" number of fathoms was that references for a fathom were already widespread and/or it allowed the line to be used to measure other things in fathoms. Mariners are notorious for making tools serve multiple purposes, both to reduce the number of tools that must be carried and maintained, but also to have multiple backups for as many functions as possible. Considering that space/weight on a sailing vessel was at a premium and that voyages were often measured in years, this seems very natural and justifiable.

 

Gimli Glider ....

Any story beginning with "holy shit", and one of those from google did, was a worth while read.

The error was a RYDM ... Read Your Damm Manual ... where they might have noticed the fuel was measured in kilograms and not gallons. The crew and the ground crew used a multiplier of 1.77 vice 0.8 in their conversions from their dip stick.

Hat's off to the pilot, and his flight experience. One article stated that many people crashed in the simulator attempting to replicate this feat.

Awarding the distinguished flying cross would be appropriate.

 

Gimli Glider ....

Any story beginning with "holy shit", and one of those from google did, was a worth while read.

The error was a RYDM ... Read Your Damm Manual ... where they might have noticed the fuel was measured in kilograms and not gallons. The crew and the ground crew used a multiplier of 1.77 vice 0.8 in their conversions from their dip stick.

Hat's off to the pilot, and his flight experience. One article stated that many people crashed in the simulator attempting to replicate this feat.

Awarding the distinguished flying cross would be appropriate.

Good story... it's so good that I've just added it to my Glad I'm not a passenger thread. Thanks!

 

As this one does too:

Traditional terms for soundings are a source for common expressions in the English language, notably "deep six" (a sounding of 6 fathoms).

Another expression derived from this, mainly in UK is 'Swinging the Lead' for dodging hard work, as swinging the lead (weight) line was considered a cushy job on board ship for taking soundings.
Max.

 

Gimli Glider ....

Any story beginning with "holy shit", and one of those from google did, was a worth while read.

The error was a RYDM ... Read Your Damm Manual ... where they might have noticed the fuel was measured in kilograms and not gallons. The crew and the ground crew used a multiplier of 1.77 vice 0.8 in their conversions from their dip stick.

Hat's off to the pilot, and his flight experience. One article stated that many people crashed in the simulator attempting to replicate this feat.

Awarding the distinguished flying cross would be appropriate.

And this is one of the truly classic cases of a cultural failure, though not of the engineering educational system this time.

The conversion factor they were looking for was how many kilograms a liter of jet fuel weighed (massed). Instead of just writing 1.77 on the charts, had they noted that it was 1.77 lb/L it would have been a really big warning flag right from the start. If the culture was that you always track your units, the natural tendency would have been to question what the units are on that naked number of 1.77 on the chart. Had they bothered to ask if the result made sense they had several opportunities to catch the mistake. First, virtually all pilots that fly with the U.S. system know that a gallon of aviation fuel weighs six pounds as a close approximation. A liter is roughly a quarter gallon, so that means that a liter of fuel weighs about 1.5 pounds. That right there should have told them that something was way off because a pound is only about half a kilogram, so the actual conversion factor should be close to 0.75 kg/L.

Then, at the stopover, the fuel usage as a fraction of the initial fuel on board should have set off mental alarms. Even as a private pilot, whenever I make a stopover and don't refuel I ALWAYS ask whether or not the fractional fuel usage makes sense. What if the engine is, for some reason, burning a lot more fuel (or, more likely, I have a leak in the fuel system somewhere)?

One thing that always makes me shake my head -- and I've seen it several times, including in regards to the Hudson River crash -- is the claim that only because the pilot was an experienced glider pilot were they aware that they needed to fly at a certain airspeed in order to maximize their range. This is Airmanship 101. The first order of business when you lose power is to establish best glide speed and it is a number that your instructor expects you to know off the top of your head (or have written down somewhere immediately visible). In many aircraft it is on a placard on the instrument panel. In the Cessna line of light aircraft (at least historically), rotating the elevator trim to full nose up will establish a hands-off airspeed very close to the optimal glide speed. In aircraft that normally cruise well above their best glide speed, including airliners and jet fighters, the normal procedure is to "zoom" to the optimal glide speed by initiating an aggressive climb to trade airspeed for altitude until you reach a speed just above the optimal glide speed at which point you nose over and establish that speed. You make the climb aggressive because you want to shed the excess airspeed, and the consequent drag, as quickly as possible.

 

Thanks you reminded me that our sailors also use knots per hour.

Knots per hour is either redundant or expresses units of acceleration. 1 knot is 1 nautical mile per hour.

 

Yeah I got my ass handed to me few posts ago so I'm aware of that.

 

 

Well I'm somewhat sure that the scientist behind that used metric to some extent. And if I'm not mistaking the Soviets were the first to have an unmanned landing on the moon.

http://en.wikipedia.org/wiki/Moon_landing

 

Yeah I got my ass handed to me few posts ago so I'm aware of that.

Sorry. since I read and respond to threads in a linear fashion, I failed to appreciate that I was piling on.