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Old 02-08-2016, 05:13 PM   #21
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I use knots and nautical miles. It's just more nautical.
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Old 02-08-2016, 05:14 PM   #22
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So "knots" are not a measure of speed?
Sorry for being a bit flippant in my wording. Here is the longer version:

In common usage (Speed Limit, Maximum Speed, etc), "speed" equates with "velocity". Some would argue more strictly that speed is a scalar while velocity is a vector but I don't think that matters here.

Velocity is the first derivative of position and time--the change in position divided by the change in time. Distance/time (eg. miles/hour). A knot is a measure of velocity: 1 nautical mile/hour.

Acceleration is the second derivative of position and time--the change in velocity (first derivative) divided by the change in time. Distance/time/time (eg. miles/hour/hour).

So when someone says "knots per hour" they're talking about an acceleration not a velocity. If they say "we were going 20 knots per hour" that says nothing about their speed (velocity) but rather that they were accelerating. What they likely meant to say was "we were going 20 nautical miles per hour" or "we were doing 20 knots".
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Old 02-08-2016, 05:24 PM   #23
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Knots is a nautical term and of course it is nautical miles per hour. A nautical mile is exactly (well maybe not quite, since the earth isn't perfectly round) one minute of longitude.

A good but maybe trivial use is measuring vertical distances on Active Captain. You can use the Path feature, but it takes time. I put the cursor on one feature and then note the longitude and scroll up or down to the next. The difference can easily be calculated: degrees * 60 + minutes equals nautical miles.

David
You mean Latitude, right? Latitude lines are evenly spaced (within the constraints you noted) 60nm apart. Spacing between longitude lines gets smaller as you approach the poles. Or am I totally mixed up here?
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Old 02-08-2016, 05:27 PM   #24
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1 min. of longitude at the equator as noted in several posts above or 1 min of latitude anywhere.
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Old 02-08-2016, 06:04 PM   #25
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I use MPH and Statute Miles 100% of the time because Knots and Nautical Miles don't relate the distance to time. If I need to go 60 miles and I go 20 MPH the entire way (-ish), I can very easily figure out the time it will take to make the journey. It just takes a step out of the process of estimating time over distance.
If I need to go 60 miles and I go 20 knots the entire way (-ish), I can very easily figure out the time it will take to make the journey. I don't have any additional step.
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Old 02-08-2016, 06:07 PM   #26
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Knots are to do with boats and airplanes and MPH and KPH is to do with cars and nautical appliances, like Sea Rays. 8^)
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Old 02-08-2016, 06:10 PM   #27
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We use knots always and nautical miles always, even when on the GICW. They are just our standard unit of measure. You give me statute and I'm going to immediately convert it to nautical in my mind. I've just conditioned myself that way.

Now, on the lake we used mph and statute miles as that was the standard there.

I admit that knots and nm can become a bit confusing when talking to a non-boater. Still it's our standard, the way we plan, the way all our equipment is set. At this point when it comes to boating, knots and nm is our first language and mph and statute miles requires us to translate.
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Old 02-08-2016, 06:11 PM   #28
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When I'm referring to distance, I use whatever measurement the applicable charts use. When in the ICW, I use statute miles.

When I'm referring to speed, I always use knots.
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Old 02-08-2016, 06:12 PM   #29
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BandB: OK how long to make the journey ? How long if they were 60 nautical miles and not statue miles ?
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Old 02-08-2016, 06:44 PM   #30
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BandB: OK how long to make the journey ? How long if they were 60 nautical miles and not statue miles ?
In my thought they were nm so 3 hours. If they were statute, I'd convert to nautical, round to 52 in my head, and it would take me 2.6 hours. Oh, typically I will leave that at 2.6 hours and not translate it to 2 hours 36 minutes.

Oh and my trick for conversion rather than multiplying by 8.689876. I deduct 10% and then I deduct 1/3 of that amount again. So 60 statute miles I subtract 6 and then subtract 2 and I'm at 52 nm. Close enough for that purpose.

I just think knots and nm on the water and assume most I'm talking to do, which may be a bad assumption. I do make the point to always note. I was copying in the above statement but I try to never say miles, always nm. To me, I think of the word miles as defaulting to statute.
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Old 02-08-2016, 07:16 PM   #31
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Maybe inland waters, lakes and rivers, is where folks stay with different units? My brothers boat mainly in those conditions and always use kmh.

A similar pattern seems to emerge from posts above. Land units for inland waters. But if your boating is primarily ocean-based then knots and nautical miles are normal use.

When brokers quote mph I think of them as either lazy and incompetent or sneaky: trying fool people into thinking the boat can cruise faster than it really can.
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Old 02-08-2016, 07:18 PM   #32
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Fortunately the nautical mile is determined by the size/shape of the earth so that it is the same distance throughout the world. Different languages may use different terms for the nautical mile, and for knots, but they are the same distances as in the English language.

Miles per hour / statute miles mean nothing to an European, or Asian. In another generation statute miles will mean nothing to a Canadian as they are slowly thinking in terms of kilometers for their land based measurements.

For a cruiser who will travel outside of the US inland rivers familiarity with knots and nautical miles is essential. Much of the written and electronic data is based on nautical miles.
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Old 02-08-2016, 07:30 PM   #33
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Both are so easy to use in the right venue, not confusing if said correctly and easy enough to convert between....


Use whatever you want...don't assume the next guy is and really don't assume they are a lesser boater for using one or the other or both....
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Old 02-08-2016, 07:34 PM   #34
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When brokers quote mph I think of them as either lazy and incompetent or sneaky: trying fool people into thinking the boat can cruise faster than it really can.
Brokers, sellers, people in general. I think of it the same way. The builders quote knots and quote range in nautical miles. I just wonder how many are fooled and subsequently disappointed by sellers or brokers quoting mph.
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Old 02-08-2016, 07:36 PM   #35
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Inland river boater and I use SM/MPH, the day marks are in SM so it easy to figure when we pass one how many miles and how much time we have left to travel. When I call a lock and tell them I'am a couple of mile out and I'll be there in 10 minutes or so they know what I'am talking about. I set all my displays to show SM and radar rings the same.


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Old 02-08-2016, 07:42 PM   #36
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I may be a fanatic when it comes to things like windlass/windless (recent thread), and yes, I do own a navy blue double breasted blazer with gold buttons, but unless I'm crossing the ocean or making some other long hike and it matters, even I use miles per hour most of the time out of habit. It's kind of like a meter or a yard. Unless I'm building furniture, the difference doesn't make enough difference to matter 99% of the time. What do I really care about that 0.15 knot/mile per hour conversion difference. And a centimeter is about half an inch, a kilogram is about a couple pounds, a 10K race is about six miles... There's a time and place for precision in life, but messing around on boats -- measuring the moving around anyway -- doesn't make enough of a difference to matter.
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Old 02-08-2016, 07:49 PM   #37
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Ok, I always thought that a nautical mile was 2000 yards, or 6000 feet vs a statute mile of 5280 feet. Therefore a knot = 1.14 mph. Is that incorrect? Seems to me my old paper charts were marked that way........btw, I use knots/nautical miles except on the ICW.
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Old 02-08-2016, 07:51 PM   #38
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Weather forecasts are now problematic, as you must listen carefully to the units, if mentioned, to determine whether the weather will be too much for your comfort. I am of course referring to the Canadian weather habit of referring to the winds on the waters of Georgia Strait in kilometers, not knots. It makes a difference of almost 2 to 1. So when my wife is listening to the forecast and repeats to me that the winds are predicted to blow 70, so we shouldn't go out, I need to know if there is a typhoon predicted, or if it just a breezy day. There is really that much difference between the winds of 70 kmh: ferries still run, waves get to 4' with enough fetch, or 70 knots: nothing goes out, damage is done. I know, the last time we had sustained 70 was in 1962, but this is just an illustration.
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Old 02-08-2016, 07:57 PM   #39
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Ok, I always thought that a nautical mile was 2000 yards, or 6000 feet vs a statute mile of 5280 feet. Therefore a knot = 1.14 mph. Is that incorrect? Seems to me my old paper charts were marked that way........btw, I use knots/nautical miles except on the ICW.
Yes, that is incorrect. Nautical mile is 6076.12 feet. A knot is 1.15078 mph. Rounded down to the nearest thousand you're right though.
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Old 02-08-2016, 08:05 PM   #40
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Weather forecasts are now problematic, as you must listen carefully to the units... I am of course referring to the Canadian weather habit of referring to the winds on the waters of Georgia Strait in kilometers, not knots. It makes a difference of almost 2 to 1. So when my wife is listening to the forecast and repeats to me that the winds are predicted to blow 70, so we shouldn't go out, I need to know if there is a typhoon predicted, or if it just a breezy day...
Well of course I'd agree with you there, in some scenarios different units do indeed matter, like that one. But if we get a weather report about wind gusts to 40 mph or 40 knots, either way I'm going to stay tied to the dock.
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