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Old 02-07-2020, 11:01   #1
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Why does iNavx use NM in it's anchor alarm?

I'm looking at using iNavx as my main anchor alarm. One thing that confuses me is the setting for Distance. As I understand it, this is the diameter of the ring it places around your anchor location that triggers a response if you drift beyond it. This setting is in nautical mile - why? When setting the anchor, I'm thinking in terms of feet - depth in feet, rode length, etc. Now I've got to convert feet into NM.

Is there a logical reason for this that I'm missing?
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Old 02-07-2020, 21:06   #2
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Re: Why does iNavx use NM in it's anchor alarm?

one nautical mile is about 6000 ft - not too hard to convert back and forth to feet, yards, or fathoms.

I’ve found setting the heading to your anchor in iNavx harder - there’s a trick to it which I don’t remember without having the app running in front of me.
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Old 03-07-2020, 00:41   #3
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Re: Why does iNavx use NM in it's anchor alarm?

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Originally Posted by dmksails View Post
I'm looking at using iNavx as my main anchor alarm. One thing that confuses me is the setting for Distance. As I understand it, this is the diameter of the ring it places around your anchor location that triggers a response if you drift beyond it. This setting is in nautical mile - why? When setting the anchor, I'm thinking in terms of feet - depth in feet, rode length, etc. Now I've got to convert feet into NM.

Is there a logical reason for this that I'm missing?
I use this app all the time, but use a little handheld gps for anchor drag usually.

I agree with you. Put out 100’ of chain and you have (less than) a 200’ swing circle to stay in. In this case I set for about 250 ft which is .041 nautical miles.

The developer has this all wrong. He’s a good guy. Maybe let him know that should be in feet.
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Old 03-07-2020, 01:30   #4
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Re: Why does iNavx use NM in it's anchor alarm?

I don't think they made any mistake there. What's wrong with NM? 0.1NM is a cable, isn't that the distance unit most people think in, in anchorages? A cable is almost exactly 100 fathoms or 600 feet. What's the problem?
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Old 03-07-2020, 09:04   #5
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Re: Why does iNavx use NM in it's anchor alarm?

Thinking about distances below 1nm my brain automatically reverts to the metric system.

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Old 03-07-2020, 09:42   #6
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Re: Why does iNavx use NM in it's anchor alarm?

[QUOTE=Dockhead;3177613]I don't think they made any mistake there. What's wrong with NM? 0.1NM is a cable, isn't that the distance unit most people think in, in anchorages? A cable is almost exactly 100 fathoms or 600 feet. What's the problem?


The problem is that you are thinking English, and the rest of the world is metric. Feet? Well, OK. Cables. Come on! You are pulling our digital legs! The point here is that units should be chosen appropriate to the required measurement. Nautical miles for anchoring is openly absurd.
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Old 03-07-2020, 10:28   #7
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Re: Why does iNavx use NM in it's anchor alarm?

I'm with Dockhead. 0.1 NM is one tenth of a nautical mile is 1 cable is 200 yards is 600 feet; 0.01 is 60 feet; 0.05 is 300 feet. Simples. You should be glad we don't get into furlongs...
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Old 03-07-2020, 11:14   #8
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Re: Why does iNavx use NM in it's anchor alarm?

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I'm with Dockhead. 0.1 NM is one tenth of a nautical mile is 1 cable is 200 yards is 600 feet; 0.01 is 60 feet; 0.05 is 300 feet. Simples. You should be glad we don't get into furlongs...
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.
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Old 03-07-2020, 11:23   #9
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Re: Why does iNavx use NM in it's anchor alarm?

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When setting the anchor, I'm thinking in terms of feet - depth in feet, rode length, etc. Now I've got to convert feet into NM.

Is there a logical reason for this that I'm missing?
Well, clearly the problem is that you just aren't using sufficient scope!
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Old 03-07-2020, 11:27   #10
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Re: Why does iNavx use NM in it's anchor alarm?

KELKARA, that was beautifull man.
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Old 03-07-2020, 11:40   #11
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Re: Why does iNavx use NM in it's anchor alarm?

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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.
Sounds like a perfectly logical method to me.
I would think though that a somewhat simpler method would be for the developer to add the ability to set whatever metric that the individual user wished to use, like most other software does.

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Old 03-07-2020, 11:46   #12
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Re: Why does iNavx use NM in it's anchor alarm?

Cables might be used over there but back in the colonies I don't recall anyone using or even mentioning cables in 45 years of boating unless referring to those big wires that go to the batteries.

On the other hand, I don't have any problem converting to fractions of or decimal parts of a nautical mile.
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Old 03-07-2020, 12:20   #13
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Re: Why does iNavx use NM in it's anchor alarm?

Yes multiple units are the issue with imperial measurment and the reason the metric system came into vogue. You can switch everything to metric for most system so you use km & m for all distance including depth. The reason nautical miles remain a mainstay in the marine wold is that they are based on degrees. A nuatical mile is actually an angulare measure and is 1 min of arc. 60 nm is 1 degree etc. This makes it very useful for navigation and keys into celestial nav but does raise problems with having to use other units for depth. A way round this may be to simply mark you anchor road in cables! Lay out half a cable of chain set the alarm for 1 cable.
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Old 03-07-2020, 12:24   #14
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Re: Why does iNavx use NM in it's anchor alarm?

I find myself straddling the systems as well. As a middle-aged Canadian I have grown up officially metric, but recall the transition in the 1970s. I know land distances in metres and km. A statue mile means little to me. Feet, yards, miles, bah... gobbledeegook.

But on the water I think of depths mostly in feet (although I'm fine with metres too), I think of distances in nautical miles, and knots for speed. But in crowded anchorages, I'm switch back to metres between boats, not nm or feet.

Actually, we measure in swimming pool lengths since my partner is an avid swimmer. I usually just ask her, "how many lengths away is that boat?"

Maybe this is why I never got into using an anchor alarm ... too confusing .
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Old 03-07-2020, 12:36   #15
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Re: Why does iNavx use NM in it's anchor alarm?

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.

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