Cruisers Forum
 


Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 05-05-2021, 08:51   #1
Registered User

Join Date: May 2021
Posts: 24
A chart plotter with audible alerts?

The navigators (used in land traffic) have offered audio warnings since the very beginning, around 20 years. How is it with plotters, are there any that gives audio alerts? I mean, if you are heading towards shallows, it would alarm the boat driver. Technically that feature is a peanut to make. I have absolutely minimal experience with chart plotters, do they give even visual alerts?
BeginnerBoater is offline   Reply With Quote
Old 05-05-2021, 09:01   #2
Registered User

Join Date: Aug 2010
Posts: 2,089
Re: A chart plotter with audible alerts?

My Raymarine's have audible and visual alerts each time I arrive at a waypoint. You can also set a depth alarm, so you'll be notified if you exceed that threshold. Depth alarm works off of the transducer, not the contour lines on the chart.

I would suspect most major brands have such features. I've never heard of a "You're about to run aground" alarm.
Shrew is offline   Reply With Quote
Old 05-05-2021, 09:32   #3
Registered User

Join Date: May 2021
Posts: 24
Re: A chart plotter with audible alerts?

Quote:
Originally Posted by Shrew View Post
I've never heard of a "You're about to run aground" alarm.

Well, that's what I'm looking for. That would be extremely useful. In case of suddenly lowering dept, the transducer may give an alert too late. Also, not all the small boats have a transducer at all. Chart plotter can be just software in your phone, a transducer can't...
BeginnerBoater is offline   Reply With Quote
Old 05-05-2021, 09:45   #4
Registered User
 
Dsanduril's Avatar

Join Date: Aug 2011
Location: Petersburg, AK
Boat: Outremer 50S
Posts: 4,000
Re: A chart plotter with audible alerts?

Most modern chartplotters that I know of using vector charts have this feature. One of the standard configurations of vector charts is to define shallow and deep values. These are then used to color the chart depending on how you have it configured. You can also set an alarm to sound or blink when you cross the shallow contour. In Raymarine Axiom, for instance, this is called "shallow water arrival". OpenCPN also has this feature. Pretty sure I've seen it in Garmin as well, but not as familiar with those plotters.
Dsanduril is offline   Reply With Quote
Old 05-05-2021, 09:45   #5
Registered User
 
Stu Jackson's Avatar

Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 8,782
Re: A chart plotter with audible alerts?

Quote:
Originally Posted by BeginnerBoater View Post
Well, that's what I'm looking for. That would be extremely useful. In case of suddenly lowering dept, the transducer may give an alert too late. Also, not all the small boats have a transducer at all. Chart plotter can be just software in your phone, a transducer can't...

Except you're missing the point of a CHARTplotter.


The CHARTS is right in front of you.


If you're not paying attention?
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, (Maple Bay Marina) SR/FK, M25, Rocna 10 (22#) (NZ model)
Stu Jackson is online now   Reply With Quote
Old 05-05-2021, 11:04   #6
Registered User

Join Date: Nov 2012
Location: Steinhatchee, FL
Posts: 140
Re: A chart plotter with audible alerts?

Quote:
Originally Posted by BeginnerBoater View Post
Well, that's what I'm looking for. That would be extremely useful. In case of suddenly lowering dept, the transducer may give an alert too late. Also, not all the small boats have a transducer at all. Chart plotter can be just software in your phone, a transducer can't...
Putting aside for the moment that the most likely reasons for running aground are inattention or that the chart does not match reality let's see if we can come up with an "about to run aground" alarm that works on a boat with no depth transducer.

Assumptions:
  • Charts exist for the area you are interested in
  • The charts accurately reflect the actual depth at the location they display (within the limits of the chart)
  • The GPS accurately reflect the actual location of the boat (within the limits of the GPS)
  • The software can accurately predict the tidal variations at your location. (Not really feasible, but let's take it as given for now).
The software will need to be able to read the depth information from the chart along with the location where that depth applies. This is possible but not trivial and the depth areas returned cover a large area on the map. Depth at an assumed location may need to be interpolated from adjacent cells.

AFIK the highest resolution NOAA charts have a 1 meter depth resolution. Not all areas have these high resolution charts. In most areas the best you will get is 2 meters. For the sake of argument let's say it can accurately interpolate the 1 meter resolution depth at your location.

GPS resolution for a cell phone is officially 4.9 meters (gps.gov). Phones try to improve on this with various assistive technology that does not have an application outside of an urban environment, so assume your location is within 4.9 meters of what is reported.

Putting it all together, your software will return a depth that is within 1 meter of the depth at your location and your location is within 4.9 meters of reality.

Now the software will need to look forward in time some distance based on your current velocity (speed and direction). The simplest way is to just extrapolate your current velocity with no changes but that is not really useful for a sailboat that may be wandering a few degrees (or more) due to wind shifts and other forces. Realistically you need to calculate the future position as a cone of possible locations based on your current location and velocity. Let's be conservative and say you can stay +- 5 degrees of your current course and velocity.

The size of the cone will increase the farther out it goes (the earlier you want to be warned about possibly running aground). At 3 knots and only one minute warning you are looking out about 90 meters ahead. Put a couple of degrees on either side of that to allow for steering inaccuracy, then add on a 4.9 meter circle for your location and you have a fairly large area you are checking for depth. Within that area you are sort of sure about the actual depth due to interpolating between actual chart readings, your assumed location, and the maximum 1 meter resolution for the depth.

While what you are proposing is possible is probably not going to deliver an accurate enough alert to be useful.

I would suggest to you that even without a depth transducer it would be simpler to create a route of where you intend to travel and set an alarm on your software if you vary from that route enough to put yourself in shallow water. It requires that you study the chart and plan the voyage to your own safety requirements, but shouldn't you be doing that regardless?

Also, consider your own experience with automotive navigation software. Does it warn you that you are too close to the shoulder or approaching traffic? Vehicles with those features have additional sensors. Similarly, a boat with a depth transducer can warn of actual low water conditions at your actual location.


Disclaimers:
  • I've tried to use data that is as accurate as I could find without spending a lot of time that I'm not getting paid for
  • I think my math is right but I'll gladly defer to anyone who can show my mistakes.
  • Lots of numbers are rounded. Those are not mistakes. I've tried to round in the direction that makes the proposed alarm program more feasible rather than less feasible.
  • Edge cases exist.
  • I may have totally misunderstood what the OP is proposing.
Be Free is offline   Reply With Quote
Old 05-05-2021, 12:01   #7
Registered User

Join Date: Jul 2018
Location: SF Bay Area
Boat: Other people's boats
Posts: 492
Re: A chart plotter with audible alerts?

Quote:
Originally Posted by Be Free View Post
Putting aside for the moment that the most likely reasons for running aground are inattention or that the chart does not match reality let's see if we can come up with an "about to run aground" alarm that works on a boat with no depth transducer.
Your list of assumptions is good, but it left out the position accuracy of the soundings, which for zone of confidence A2 would be 20 m.

Still, such a look-ahead feature can be found in fancier navigation packages. For example, take a look at the "security cone" or "route planning" screenshots for TZ Navigator: https://mytimezero.com/tz-navigator.

Personally I think it would be a useful safety net, but also one that generally shouldn't be triggered if one is properly paying attention (false alarms excepted, as any course that winds between shallows would trigger them).
requiem is offline   Reply With Quote
Old 05-05-2021, 12:46   #8
Registered User

Join Date: Aug 2010
Posts: 2,089
Re: A chart plotter with audible alerts?

Quote:
Originally Posted by Dsanduril View Post
Most modern chartplotters that I know of using vector charts have this feature. One of the standard configurations of vector charts is to define shallow and deep values. These are then used to color the chart depending on how you have it configured. You can also set an alarm to sound or blink when you cross the shallow contour. In Raymarine Axiom, for instance, this is called "shallow water arrival". OpenCPN also has this feature. Pretty sure I've seen it in Garmin as well, but not as familiar with those plotters.
I guess I never dug that deep into the settings because I never use them. I don't even set a generic depth alarm.

I plot my course out ahead of time, and monitor the depth gauge and chart depths.

Those alerts get pretty annoying coming in to harbors, anchorages, and marina's.
Shrew is offline   Reply With Quote
Old 05-05-2021, 13:11   #9
Registered User

Join Date: May 2021
Posts: 24
Re: A chart plotter with audible alerts?

Quote:
Originally Posted by Stu Jackson View Post
Except you're missing the point of a CHARTplotter.


The CHARTS is right in front of you.


If you're not paying attention?

I'd rather not pay attention to the chart as long as there's no specific reason. If there's deep water all around the boat, I'd rather enjoy the lake view. And an audio warning would alert me and make me look at the chart and decide if I need to change the course or not.
BeginnerBoater is offline   Reply With Quote
Old 05-05-2021, 13:58   #10
Registered User

Join Date: May 2021
Posts: 24
Re: A chart plotter with audible alerts?

Quote:
Originally Posted by Be Free View Post
Putting aside for the moment that the most likely reasons for running aground are inattention or that the chart does not match reality let's see if we can come up with an "about to run aground" alarm that works on a boat with no depth transducer.

Assumptions:
  • Charts exist for the area you are interested in
  • The charts accurately reflect the actual depth at the location they display (within the limits of the chart)
  • The GPS accurately reflect the actual location of the boat (within the limits of the GPS)
  • The software can accurately predict the tidal variations at your location. (Not really feasible, but let's take it as given for now).
The software will need to be able to read the depth information from the chart along with the location where that depth applies. This is possible but not trivial and the depth areas returned cover a large area on the map. Depth at an assumed location may need to be interpolated from adjacent cells.

AFIK the highest resolution NOAA charts have a 1 meter depth resolution. Not all areas have these high resolution charts. In most areas the best you will get is 2 meters. For the sake of argument let's say it can accurately interpolate the 1 meter resolution depth at your location.

GPS resolution for a cell phone is officially 4.9 meters (gps.gov). Phones try to improve on this with various assistive technology that does not have an application outside of an urban environment, so assume your location is within 4.9 meters of what is reported.

Putting it all together, your software will return a depth that is within 1 meter of the depth at your location and your location is within 4.9 meters of reality.

Now the software will need to look forward in time some distance based on your current velocity (speed and direction). The simplest way is to just extrapolate your current velocity with no changes but that is not really useful for a sailboat that may be wandering a few degrees (or more) due to wind shifts and other forces. Realistically you need to calculate the future position as a cone of possible locations based on your current location and velocity. Let's be conservative and say you can stay +- 5 degrees of your current course and velocity.

The size of the cone will increase the farther out it goes (the earlier you want to be warned about possibly running aground). At 3 knots and only one minute warning you are looking out about 90 meters ahead. Put a couple of degrees on either side of that to allow for steering inaccuracy, then add on a 4.9 meter circle for your location and you have a fairly large area you are checking for depth. Within that area you are sort of sure about the actual depth due to interpolating between actual chart readings, your assumed location, and the maximum 1 meter resolution for the depth.

While what you are proposing is possible is probably not going to deliver an accurate enough alert to be useful.

I would suggest to you that even without a depth transducer it would be simpler to create a route of where you intend to travel and set an alarm on your software if you vary from that route enough to put yourself in shallow water. It requires that you study the chart and plan the voyage to your own safety requirements, but shouldn't you be doing that regardless?

Also, consider your own experience with automotive navigation software. Does it warn you that you are too close to the shoulder or approaching traffic? Vehicles with those features have additional sensors. Similarly, a boat with a depth transducer can warn of actual low water conditions at your actual location.


Disclaimers:
  • I've tried to use data that is as accurate as I could find without spending a lot of time that I'm not getting paid for
  • I think my math is right but I'll gladly defer to anyone who can show my mistakes.
  • Lots of numbers are rounded. Those are not mistakes. I've tried to round in the direction that makes the proposed alarm program more feasible rather than less feasible.
  • Edge cases exist.
  • I may have totally misunderstood what the OP is proposing.
Thank you for your detailed follow-up. Yes, there are plenty of assumptions that must be fulfilled in order to make the alarms efficient. My original idea was being able to run the boat on a lake which is generally deep water but may randomly have swallows under the surface. As the trip would be purely a joy ride, I'd like to drive without prior route planning. So, the route would be "planned" more or less on the fly. Near the coastline, there probably aren't any other options than look at the chart, but on the open lake, there usually is 10...30 m deep. Few exceptions exist, and those are the ones I'd like to be alerted to. Yes, I could look at the chart all the time and get the info there, but that would ruin the whole idea about the joy ride. For that purpose, inaccuracies depth information and GPS are well within limits: In rare swallows, I could use sufficient safety margin to overcome these inaccuracies.

About the car navigators: You don't really need to look at the map at all, but you'll be guided by voice. No matter how long the trip and how many turns there will be, you will stay on the right path based purely on the voice commands. If auto navigators didn't have voice, that would reduce their usefulness a lot. Of course, the auto navi does not warn about other cars or other safety risks, just like chart plotter doesn't show other boats, sea animals (or swimmers) in the water or a sinker. But the chart plotter knows the swallows and also where the boat is currently heading, it doesn't take much intelligence to conclude if there's something to worry about in front of you.
BeginnerBoater is offline   Reply With Quote
Old 05-05-2021, 14:08   #11
Registered User
 
Stu Jackson's Avatar

Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 8,782
Re: A chart plotter with audible alerts?

Quote:
Originally Posted by BeginnerBoater View Post
I'd rather not pay attention to the chart as long as there's no specific reason. If there's deep water all around the boat, I'd rather enjoy the lake view. And an audio warning would alert me and make me look at the chart and decide if I need to change the course or not.

We all like the view.


But I suggest you read (or re-read) Chapman's or any other qualified navigation book.


From your username you're new. And a lake sailor. Not a bad start.


In order to continue, we use the phrases "get your head out of the boat" (the view but lots more) and "don't stare at screens".


Safe navigation on the water is much more than just a machine alerting you to things that you should be aware of in you trip plans in the first place.


And if it's not on the charts and you don't have a depthsounder plugged into the system, how's it gonna find that "unknown" shallow spot?


Good luck out there.
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, (Maple Bay Marina) SR/FK, M25, Rocna 10 (22#) (NZ model)
Stu Jackson is online now   Reply With Quote
Old 05-05-2021, 14:08   #12
Registered User

Join Date: Aug 2010
Posts: 2,089
Re: A chart plotter with audible alerts?

Quote:
Originally Posted by BeginnerBoater View Post
I'd rather not pay attention to the chart as long as there's no specific reason. If there's deep water all around the boat, I'd rather enjoy the lake view. And an audio warning would alert me and make me look at the chart and decide if I need to change the course or not.

What you describe sound more appropriate for a beach cat or a sunfish.

What size boat is this?

What is the body of water you're navigating on?
Shrew is offline   Reply With Quote
Old 05-05-2021, 14:19   #13
Registered User

Join Date: May 2021
Posts: 24
Re: A chart plotter with audible alerts?

Quote:
Originally Posted by Stu Jackson View Post
We all like the view.


But I suggest you read (or re-read) Chapman's or any other qualified navigation book.


From your username you're new. And a lake sailor. Not a bad start.


In order to continue, we use the phrases "get your head out of the boat" (the view but lots more) and "don't stare at screens".


Safe navigation on the water is much more than just a machine alerting you to things that you should be aware of in you trip plans in the first place.


And if it's not on the charts and you don't have a depthsounder plugged into the system, how's it gonna find that "unknown" shallow spot?


Good luck out there.
Thank you for your message. Exactly, I'd rather not spend my time staring at the screens. That's why I'd like to utilize my ears... (audible warnings). You're right: what's not on the map, can't be alerted. I'm ready to accept that, and I only wish to get the visual alert the plotter gives audible also. My eyes can't catch a rock right below the water surface (from few cm's to 50 cm) which would damage my outboard engine.

Thank you for wishing me good luck. But honestly, I'd like to reduce the share of luck and replace it with modern technology...
BeginnerBoater is offline   Reply With Quote
Old 06-05-2021, 09:03   #14
Registered User
 
Flatswing's Avatar

Join Date: Jan 2020
Location: Hilton Head, SC, USA
Boat: DeFever Raised Pilot House 49
Posts: 129
Re: A chart plotter with audible alerts?

Quote:
Originally Posted by BeginnerBoater View Post
I'd rather not pay attention to the chart as long as there's no specific reason. If there's deep water all around the boat, I'd rather enjoy the lake view. And an audio warning would alert me and make me look at the chart and decide if I need to change the course or not.
A) as others have stated clearly, virtually all chart plotters have simple visual (colorimetric) depth warnings, most have audible depth alarms
B) even rudimentary depth finders like the Hawkeye on my dinghy have audible alarms. But many of us turn them off as they are distracting in critical nav environments.

Gotta say though that if glancing at the chart plotter from time to time is too inconvenient for you, well -you know.
Flatswing is offline   Reply With Quote
Old 06-05-2021, 09:53   #15
Registered User

Join Date: Feb 2015
Location: Somewhere warm
Boat: Morgan 462
Posts: 1,591
Re: A chart plotter with audible alerts?

Quote:
Originally Posted by BeginnerBoater View Post
I'd rather not pay attention to the chart as long as there's no specific reason. If there's deep water all around the boat, I'd rather enjoy the lake view. And an audio warning would alert me and make me look at the chart and decide if I need to change the course or not.

Beginner, when you gain more experience, perhaps running aground a few times, you will see that your attitude may change.

There is always a "specific reason" to look at a chart at reasonable intervals whether or not you sense any danger. The specific reason is, you are piloting a boat.

But I do see the logic in your suggestion, since none of us are perfect and we sometimes neglect to pay attention. And I don't think it's unreasonable to question whether such a warning function could be programmed into chartplotters.
__________________
No shirt, no shoes, no problem!
waterman46 is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Icom IC M505 only receiving when squelch turned down til background noises audible. davefrediam Marine Electronics 1 09-07-2018 01:57
Audible Overheat Alarm For Engine Pam Baker Engines and Propulsion Systems 3 25-04-2013 05:33
Audible Temp Gauge old bradders Engines and Propulsion Systems 4 05-11-2010 12:23

Advertise Here


All times are GMT -7. The time now is 13:20.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.