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

[fxykty]

Originally Posted by Dockhead

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.

I have to ask, how did setting a guard zone on your radar stop your boat from swinging into the cutter? Did it warn you and you took avoiding action? Or do you think you would have swung into the cutter if you hadn’t set a guard zone?

[Dockhead]

Originally Posted by fxykty

I have to ask, how did setting a guard zone on your radar stop your boat from swinging into the cutter? Did it warn you and you took avoiding action? Or do you think you would have swung into the cutter if you hadn’t set a guard zone?

Yes, it would have warned me if I started swinging too close. One would hope that there would be enough time to get the engine started and move away. There were pretty big distances involved -- I had 100 meters of chain out.



But in the event we swung enough the same with the cutter, that there was no problem despite the big difference in size.

[Mike OReilly]

Originally Posted by Dockhead

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.

I tend to leave iNavx running most of the time, but probably not all. Once I have a clear swing pattern I'm less concerned. It only takes a few seconds to boot up after all. But if any blow should come up, especially at night, it usually stays on, within reach of me. I can then glance at it periodically to confirm my other sensory input (visual, auditory, tactile).

Originally Posted by Dockhead

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.

I've used radar to check distances sometimes, but not used the guard zones. I'll keep it in mind as another tool in the toolkit.

[Dockhead]

Originally Posted by Mike OReilly

. . .I've used radar to check distances sometimes, but not used the guard zones. I'll keep it in mind as another tool in the toolkit.

IF the radar set has adequate target discrimination, then the guard zones are one of the most useful features. A great enhancement to watchkeeping.


The best feature by far of my Navico 4G radar. The one outstanding thing about this radar is target discrimination, so the guard zones work fantastically well with almost no false alarms. Everything else about this radar is average (range, bearing discrimination), or utter crap (MARPA). Maybe close-in performance could be described as above-average. Not a huge fan of this radar, but on the other hand, the superb guard zones almost justify it by themselves.

[requiem]

Originally Posted by 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

Well, an arc minute of latitude is a bit fuzzy for precise work, but it works as an convenient approximation and particularly so when working on paper charts. That's why it's been defined as a specific distance that's conveniently close to an arc-minute at around 45° N. Of course, anything that needs precision would likely be using radians instead of those archaic Babylonian degrees.

It occurs to me that one could then use a "nautical mil" of 6.4 km in place of the nautical mile and easily be able to break it down into 8ths (800 m), 16ths (400 m), etc. A bit ironic, I guess.

[requiem]

Originally Posted by requiem

Well, an arc minute of latitude is a bit fuzzy for precise work, but it works as an convenient approximation and particularly so when working on paper charts. That's why it's been defined as a specific distance that's conveniently close to an arc-minute at around 45° N. Of course, anything that needs precision would likely be using radians instead of those archaic Babylonian degrees.

It occurs to me that one could then use a "nautical mil" of 6.4 km in place of the nautical mile and easily be able to break it down into 8ths (800 m), 16ths (400 m), etc. A bit ironic, I guess.

Edit: to be more on-topic, I personally dislike automatic scale-changes. If I'm zooming in and out it's often for context, and that having the units change on me breaks that.

[PirateGuy]

Originally Posted by Mike OReilly

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.

Anchor alarms and good anchoring techniques aren’t mutually exclusive.

Sensory awareness is fundamental to successful and safe small blue water boating. Unfortunately, we all have to sleep sometimes. Our bodies don’t work perfectly all the time and we can sleep deeper or shallower depending on health - even diet. I believe you sail with a partner, so you have a redundancy that many don’t. Crew are usually a poor substitute for a captain’s knowledge of his own boat.
I mostly single hand or sail with eye candy. My sense of responsibility to myself, my boat, my companions, my neighbors and preserving the local environment encourage me to use all the reasonable safety procedures and tools available.
You have the iNavx app. The anchor alarm is easy to set. Being a Luddite has its charms, life is way too often needlessly complicated and stressful, but being mindful of our responsibilities to others and our quickly vanishing natural spaces should be a goal to differentiate most cruising sailors from daytrippers.

[Mike OReilly]

Originally Posted by PirateGuy

Anchor alarms and good anchoring techniques aren’t mutually exclusive.

Sensory awareness is fundamental to successful and safe small blue water boating. Unfortunately, we all have to sleep sometimes. Our bodies don’t work perfectly all the time and we can sleep deeper or shallower depending on health - even diet. I believe you sail with a partner, so you have a redundancy that many don’t. Crew are usually a poor substitute for a captain’s knowledge of his own boat.
I mostly single hand or sail with eye candy. My sense of responsibility to myself, my boat, my companions, my neighbors and preserving the local environment encourage me to use all the reasonable safety procedures and tools available.
You have the iNavx app. The anchor alarm is easy to set. Being a Luddite has its charms, life is way too often needlessly complicated and stressful, but being mindful of our responsibilities to others and our quickly vanishing natural spaces should be a goal to differentiate most cruising sailors from daytrippers.

I'm not sure what you're insinuating, but it's starting to feel insulting. I've never said they were exclusive, nor that someone shouldn't use one. Use your anchor alarm if it works for you. Cruisers have lived for many decades, without it. Most seem to manage. But if it's useful to you, by all means use it.

When it comes to electronics I'm far from a Luddite. I also have a decent appreciation for the limits to this technology. So use it if you find it useful, but certainly don't make it your main tool. That would be irresponsible to others.

[waterman46]

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.

Doing all that math keeps your brain in good condition. But there are dozens of anchor alarm apps out there that use feet or meters so just switch. . My problem is I have not found an Android app anchor alarm that wont wake me at 3 AM with a false alarm.

[iNavX]

Originally Posted by dmksails

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?

Check your settings, under More/Settings/Units.

Under distance there's a "Distance" and "Sub Distance" setting. The default Sub Distance if you're using NM is also NM. Change this to Yds.

It will change the unit displayed at the anchor alarm to feet. If you set the distance to Meters, it will show the anchor alarm in meters. You may need to change it once with the +/- for the unit display to change when you go back to the screen.

The granularity does not change, however. The +/- buttons are still moving by .01 Nm, but the display units will change to feet or meters.

So you go from 61' to 122' to 183' (.01, .02, .03 Nm respectively).

I will pass this back to the developer. It seems like a nice feature would be to be able to enter exact feet or meters here instead of .01 Nm steps since those are fairly big and aren't as relatable to how we may mark our chain (e.g. 25', 10m, etc.).

[sarita]

Originally Posted by dmksails

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?

Boat Beacon has an anchor alarm which shows the distance in Feet or Meters depending on your preference. It also has a useful offset/rhode distance setting so you can back away from where you dropped the anchor and with your boat pointing towards the anchor set the anchor from there.

[Safari38LH]

Check out Aqua Maps. Excellent anchor alarm!

[lenseman]

Originally Posted by Clivevon

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...

and Rod, Poles and Perches.


Only a numpty wants to use Landlubber terms.


You probably set the anchor alarm once you have fully bedded in the anchor and not at the moment you drop the hook? WRONG.



Ho-Hum


And just to help you out, A cable is about 185 metres.

[paul2884]

At least nautical miles are a internationaly used measurement, who apart from the US uses feet? Most of the world are metric, before the UK went metric yards or fathoms would have made sense but now Nautical miles or meters would make are the most logical for most of the world

[Chotu]

Originally Posted by paul2884

At least nautical miles are a internationaly used measurement, who apart from the US uses feet? Most of the world are metric, before the UK went metric yards or fathoms would have made sense but now Nautical miles or meters would make are the most logical for most of the world

Uh... that’s why he said you can choose meters.