Why does iNavx use NM in it's anchor alarm?

[Dockhead]

Originally Posted by Kelkara

So I get depth off the chart in fathoms, look up the state of the tide in feet and add freeboard in inches, convert back to fathoms add to water depth, then multiply by scope, and re-convert back to feet to measure out my rode, then convert to nautical miles to set my anchor alarm, log my position in minutes of arc, and look up cable in a dictionary.


couldn't be simpler.

Feet? We don't use feet. Depth in meters.

The nautical mile is metric, as far as I know, which I reckon means the cable is too. Anyway those units are in the blood of anyone who had spent a certain amount of time at sea.

[Dockhead]

There are different cables, just like there ate different miles, but the International Cable is exactly 1/10 of a nautical mile. As such I believe it's also a metric unit, but I will need to look that up to be sure.

Originally Posted by svfinlandia

One of the problems with using a Cable as a unit of measure is that it is not necessarily a defined length.
According to Wikipedia: A cable length or length of cable is a nautical unit of measure equal to one tenth of a nautical mile or approximately 100 fathoms. Due to anachronisms and varying techniques of measurement, a cable length can be anywhere from 169 to 220 metres, depending on the standard used.

Al, S/V Finlandia

[Chotu]

The nautical mile isn’t metric or the other system. It’s its own system:

A nautical mile is a unit of measurement used in air, marine, and space navigation, and for the definition of territorial waters. Historically, it was defined as one minute of latitude along any line of longitude. Today the international nautical mile is defined as exactly 2025 yards, or 1852 meters. But the original definition makes it non-system specific.

This isn’t real a battle between systems of units. It’s a problem with scale.

It’s silly to have a user select a distance that is clearly in the scale of meters and feet/yards on a scale that’s in miles and kilometers.

Definitely an error on the part of the developer.

[IslandHopper]

Originally Posted by Chotu

It’s silly to have a user select a distance that is clearly in the scale of meters and feet/yards on a scale that’s in miles and kilometers.

Definitely an error on the part of the developer.

No it's not! commercially it's all that is used, we don't switch our units of measurements in our electronics to suit what the vessel is doing at a given time, they remain in Nautical Miles for any distance, INCLUDING distance to anchor....

Doing the conversion is easy enough if you need to...........

[Chotu]

Originally Posted by IslandHopper

No it's not! commercially it's all that is used, we don't switch our units of measurements in our electronics to suit what the vessel is doing at a given time, they remain in Nautical Miles for any distance, INCLUDING distance to anchor....

Doing the conversion is easy enough if you need to...........

Completely false. (See pic of Garmin unit anchor drag setting in FEET)

It has the option to see all units in KMS/Metric as well. That’s normal international programming.

Proper UI/UX dictates smaller units for smaller scales and is implemented everywhere. Expecting the user to accurately do conversions while anchoring is ridiculous. The iNavX developer, though a really friendly and nice guy, got this wrong. I’m sure he’d appreciate the feedback.

Are you going to measure the thickness of your hull and how much chain you pay out in nautical miles too?? LOL

[PirateGuy]

Originally Posted by Mike OReilly

Maybe this is why I never got into using an anchor alarm ... too confusing .

An anchor alarm can be a life saver. Or at least a boat saver, including boats in the anchorage around you.

I like the iNavx app - it’s pretty easy to use and the Sea of Cortez charts are well supported. I sometimes forget to turn off the anchor alarm when turning off the app (or my iPad has gone dead by morning. Then, when the alarm goes off inadvertantly, my blood runs cold. One night of dealing with a fouled anchor dragging was enough to make a believer out of me.

As I said, setting the distance to the anchor in iNavx is no problem for me (0.01 NM is 60 ft, 10 fathoms or about 20 meters) but the anchor heading setting is a bit awkward.

[Dockhead]

Originally Posted by Chotu

The nautical mile isn’t metric or the other system. It’s its own system:. .

Now I'm home and looked it up --


The nautical mile is indeed recognized and defined in the International System of Units, which is the embodiment of the Metric System, albeit as a non-SI unit.

Originally Posted by IslandHopper

No it's not! commercially it's all that is used, we don't switch our units of measurements in our electronics to suit what the vessel is doing at a given time, they remain in Nautical Miles for any distance, INCLUDING distance to anchor....

Doing the conversion is easy enough if you need to...........

Indeed. "Commercial it's all that is used" -- i.e., NM is what professional seamen use. If you can't convert you NM to cables and meters or fathoms or whatever you need, in a split second in your mind, then you need some remedial education . . .

[Chotu]

Originally Posted by Dockhead

Now I'm home and looked it up --


The nautical mile is indeed recognized and defined in the International System of Units, which is the embodiment of the Metric System, albeit as a non-SI unit.






Indeed. "Commercial it's all that is used" -- i.e., NM is what professional seamen use. If you can't convert you NM to cables and meters or fathoms or whatever you need, in a split second in your mind, then you need some remedial education . . .

The nautical mile was invented in 1594. The metric system was invented in 1670.

It’s not defined as part of the metric system, as it existed before there was a metric system. It was merely incorporated into it by the French measuring out how many meters are in a nautical mile.

Absolutely nothing to do with the metric system. It has to do with navigation

I thought this was common knowledge?

[IslandHopper]

Originally Posted by Chotu

Completely false. (See pic of Garmin unit anchor drag setting in FEET)

It has the option to see all units in KMS/Metric as well. That’s normal international programming.

Proper UI/UX dictates smaller units for smaller scales and is implemented everywhere. Expecting the user to accurately do conversions while anchoring is ridiculous. The iNavX developer, though a really friendly and nice guy, got this wrong. I’m sure he’d appreciate the feedback.

Are you going to measure the thickness of your hull and how much chain you pay out in nautical miles too?? LOL

Rubbish and your missing the point of my post, you said the developer stuffed up and i'm telling you they didn't! i never said the option to change the units are not available you just did! i'm also telling you we don't change the units of measurement in any of our GPS/ECDIS units just because we have gone from steaming to anchoring, thats just plain stupid!......the instruments remain in NM's....period!

We know how much chain we have, we know the bow to waterline measurement, we know the depth, we know how much to put out, if i ask for 5 shackles on the water i know exactly how much chain is out, doing the conversion is dead easy....

Hull thickness.............Lol

[requiem]

Originally Posted by Chotu

The nautical mile was invented in 1594. The metric system was invented in 1670.

It’s not defined as part of the metric system, as it existed before there was a metric system. It was merely incorporated into it by the French measuring out how many meters are in a nautical mile.

Absolutely nothing to do with the metric system. It has to do with navigation

I thought this was common knowledge?

Common knowledge is usually pretty confused when it comes to fine details.

Most archaic units have indeed been re-sized and redefined in terms of the metric system. It's not a big deal, since the precise lengths have changed over the years, and often more than one definition has been in play at the same time. For example, the average American probably doesn't know which particular "foot" their home state uses for land measurements.

The current version of the SI brochure has dropped the nautical mile from the table of "Non-SI units accepted for use with the SI". I imagine it's covered by the paragraph just after that table, which says:

There are many more non-SI units, which are either of historical interest, or are still used in specific fields (for example, the barrel of oil) or in particular countries (the inch, foot and yard). The CIPM can see no case for continuing to use these units in modern scientific and technical work. However, it is clearly a matter of importance to be able to recall the relation of these units to the corresponding SI units and this will continue to be true for many years.

[groundtackle]

Maybe someone already pointed out that the nautical mile is not some arbitrary archaic invention. A nautical mile as I’m sure most of us know is the distance covered by one minute of latitude. So until a circle has something other than 360 degrees a nautical mile is both useful and logical and is in fact the most sensible measure of distance when navigating.
By the way you’d have to reprogram every calculator and re write every trigonometry text book and god knows what else if you want to change the degrees in a circle.
Nick

[Mike OReilly]

Originally Posted by PirateGuy

An anchor alarm can be a life saver. Or at least a boat saver, including boats in the anchorage around you.

Yes, but I prefer old fashion awareness and good anchoring technique.

Actually, I do sometimes leave the plotter on (I use iNavX) to track my normal swing pattern. Then, if things get ugly I can glance at it from down below to see if we've exceeded the norm. So I guess I use the tool, but more manually.

Not arguing against anchor alarms. I've used them, but I just haven't found the need for one.

[Smokeys Kitchen]

Originally Posted by IslandHopper

Rubbish and your missing the point of my post, you said the developer stuffed up and i'm telling you they didn't! i never said the option to change the units are not available you just did! i'm also telling you we don't change the units of measurement in any of our GPS/ECDIS units just because we have gone from steaming to anchoring, thats just plain stupid!.

Not stupid at all. My Simrad radar displayed on my B&G Zeus has NM for most of the ranges when I am out and moving. As I come into an anchorage and I want to see the boat distances from me, I dial down the scale on the radar and it goes from 1/8 NM to 400 ft at the outer ring. Being a Yank - I am way more familiar with feet when in close proximity than other units of measure and it works well for us.

It's good to stay at least a half a football field away from your nearest neighbor. (That's 50 yards / 150 feet to you non-footballers).

[Dockhead]

Originally Posted by Chotu

The nautical mile was invented in 1594. The metric system was invented in 1670.

It’s not defined as part of the metric system, as it existed before there was a metric system. . . .

Incorrect facts and faulty logic. The "metric system" was not invented on any one date, and certainly not in 1670 when it was not even a glimmer in its father's eye. Its roots go back to the French Revolution in the 1790's, with the invention of the kilogram and meter to replace archaic measures of weight and length, but that is not yet any actual "metric system". It wasn't until the middle of the 19th century that the idea of "base units" appeared, and only in 1861 was there for the first time even any proposal for a comprehensive metric system. An actual "metric system" can be said to exist only after the 1875 Treaty of the Meter, which established the International Committee of Weights and Measures. At this time the nascent metric system is still only concerned with mass and length. Not until 1948 do we have something like the modern metric system, covering units of measurements in various fields and all tied in to seven fundamental units.

See: https://en.wikipedia.org/wiki/Histor..._metric_system

OK, those were the facts. Now the logic: Why would the age of any unit, preclude it from being part of the metric system? The degree Celsius was invented in 1743. It was incorporated into the metric system in 1948. So I guess the degree Celsius has nothing to do with the metric system, "as it existed before there was a metric system"? The degree Celsius, unlike the nautical mile, is an actual SI unit.

Originally Posted by Chotu

1. It was merely incorporated into it . . .

2. Absolutely nothing to do with the metric system.

This is a rather silly thing to be arguing about, but really -- how can something be "incorporated into" something and at the very same time, have "absolutely nothing to do with", that something? This is a ridiculous contradiction.

Anyway, as I said, it's a silly argument and I regret having started it. My bad.

Metric, or not, the nautical mile is noble unit of measure, recognized by SI, if not an actual SI unit, which has an honored place among other units used for serious purposes. Unlike the statute mile, the pound, the ounce, and the inch, which are merely archaisms with no usefulness and no connection to any fundamental parameters of anything, the nautical mile represents, as many in this thread have posted, a minute of latitude along any line of longitude, and so forms a part of the whole system of coordinates of the earth.

The kilometer is not relatable to the system of coordinates of the earth -- the earth is not built out of any fundamental units -- so the nautical mile is better than the km for our purposes. More beautiful, more useful. We read distance in charts by simply putting the divider on a longitude line. The whole fundamental idea of the metric system is to make units relatable to each other -- the nautical mile is relatable to the most important units in our world, namely degrees and minutes on our charts.

The cable is no less noble, as a decimal sub-unit of the nautical mile.

Where you go from there, is up to you. I'm a metric person, so for me depth is meters and only and always meters. I think of distance easily in meters, since that is what I use on land, and converting back and forth from miles and cables to meters is no difficulty whatsoever for me. 100 meters is roughly half a cable, and that roughly is usually close enough, and if you want to be less rough, a cable is about 185m, something I have no trouble remembering.

However, fathoms play a small role in my world, as that is how you measure cordage with your outspread arms. Feet, inches, and pounds have long been banished from my consciousness, but the fathom is concretely useful, at least for inventoring cordage. A chart with depth marked in fathoms wouldn't bother me that much, although feet drive me up the wall.

Also, I mark my anchor chain in SHOTS of chain, except I have my own made-up shot unit -- which is 30 meters, so roughly 3 meters longer than an actual shot, which is defined as 15 fathoms. OK, so shoot me. I call it a "metric shot".

[Dockhead]

Originally Posted by Mike OReilly

. . . Actually, I do sometimes leave the plotter on (I use iNavX) to track my normal swing pattern. Then, if things get ugly I can glance at it from down below. . . to see if we've exceeded the norm. So I guess I use the tool, but more manually.

Not arguing against anchor alarms. I've used them, but I just haven't found the need for one.

I always leave my plotters on at anchor -- as a matter of principle. Not only so that I can see at a glance where we are swinging, but also in case anchor drags and we have to bug out -- so I can instantly plot an escape route.


Another excellent anchor alarm is a radar guard zone. I often leave radar running at anchor, when I need to be sure about my distance to other vessels or land features. Set a guard zone and it will wake you up if you get too close.



One memorable example of that was anchored in very deep water in Ushant, not far from a French coast guard cutter, and in three days of gales to boot. For different reasons there was not really any other place to anchor. At high tide, the water was something like 40m deep. I sure as hell didn't want to swing into the steel coast guard cutter, so I set a guard zone. We didn't.