Arduino based anchor watch

[goboatingnow]

Originally Posted by noelex 77

Exactly. This is responsible for many of the false positive alarms. Pity, when it is easy to fix. You don't need sophisticated integrated electronics with heading information (although this will give a slightly better result).



Good anchoring gear is the most important factor, but anchor alarms provide a valuable back up. Unfortunately, many cruisers set these alarms incorrectly.

The problem is many nav devices required quite complex setup to activate the drop point , certainly my ray marine lighthouse 2 has it buried menus deep.

Then others have the gear below decks , it’s not conducive to good anchoring to run below just when you want to drop the hook.

That’s my whole reason for this project , simple button at the helm , press once at the drop point ,press again after digging in

[noelex 77]

Originally Posted by goboatingnow

The problem is many nav devices required quite complex setup to activate the drop point , certainly my ray marine lighthouse 2 has it buried menus deep.

It is disappointing that many chartplotters have very poor anchor alarms. Some cannot be set correctly even after wading through the menus.

Originally Posted by goboatingnow

Then others have the gear below decks , it’s not conducive to good anchoring to run below just when you want to drop the hook.

That’s my whole reason for this project , simple button at the helm , press once at the drop point ,press again after digging in

This would be more convenient and I think your project is worthwhile, but there is no need to run below. When anchoring, the track will be recorded and this will normally enable the drop point to be determined at leisure once the anchoring process is finished. However, it is important to displace the centre of the anchor alarm by the distance between the GPS antenna and the bow. Unfortunately, many neglect this important step.

There are alternative techniques that also work well. The anchor location can be roughly determined in stronger wind by using the rode length, distance between the bow and GPS antenna and wind direction. Any error can be seen as the yacht moves around the swing circle.

[muttnik]

Originally Posted by goboatingnow

There will be a push button at the wheel , at the designated anchor drop ( or shortly thereafter ) the button is pushed and the anchor watch system records the gps location

A subsequent push then records ( assuming you’ve dug in your anchor the max swing radius.

Interesting thread which has made me revisit my oft-pondered thoughts on how I'd implement an anchor alarm. The "where exactly *is* the anchor?" question is a knotty one. Do please be brutal if I've missed something and am stating the obvious. This is also just musings so criticism will not be taken personally :-)

I *think* from the above your second button press is purely to determine swinging radius. However the centre of that radius won't be at the drop point. Not only will current (or engine) move you as the anchor goes down, the bow will inevitably blow off. More importantly, the anchor may take some distance to dig in. When I first thought about this I thought about a manual correction but the desire to do this with button presses is laudable. Chain counter / GPS / sensor location / heading / depth info could be combined to calculate where the anchor hits bottom but that's not necessarily where it digs in.

If digging in the anchor under power, might all the parameters be obtained from the second button press alone? ie if the chain goes roughly straight when digging in under power, combining GPS, heading, depth, chain length and corrections for catenary, bow height, distance of bow roller to the chain sensor you have a reasonable idea of both centre and radius of your swinging circle. Building chain counter functionality with the arduino would be no bad thing and allow for automatic recalculation of swinging circle if you let out more chain after digging in.

Obviously this approach doesn't work if you're anchoring under sail without sufficient wind or current to make the chain go straight.

[Jack C]

Its desirable to check that the anchor is set by diving. Then you can set the anchor position. If the anchor is so dug in that you cannot find it, then you may not need the alarm.

[acunningham]

Anchor trip buoys are anti-social in crowded anchorages, but in uncrowded anchorages might it be possible to put a battery powered GPS receiver inside a trip buoy, and have it relay the buoy's position to an alarm on the boat via radio? This might offer a more accurate measurement of the anchor's location. As a bonus, you have a trip line deployed in case the anchor gets snagged.

[acunningham]

If you want to get really fancy, how about an accelerometer or vibration detector in the anchor itself? It could relay alarms to the boat via ultrasonic signals through the water, some sort of high frequency vibrations through the chain, or radio via a trip buoy.


The hard part would presumably be making it strong enough to withstand all the impacts and scrapes that anchors suffer.

[goboatingnow]

Lads let’s avoid the dilithium crystal mission creep problem. That’s for V2

[goboatingnow]

Originally Posted by Jack C

Its desirable to check that the anchor is set by diving. Then you can set the anchor position. If the anchor is so dug in that you cannot find it, then you may not need the alarm.

Short of doning full scuba , you can dive my anchors in cold northern waters thanks

[goboatingnow]

Originally Posted by acunningham

Anchor trip buoys are anti-social in crowded anchorages, but in uncrowded anchorages might it be possible to put a battery powered GPS receiver inside a trip buoy, and have it relay the buoy's position to an alarm on the boat via radio? This might offer a more accurate measurement of the anchor's location. As a bonus, you have a trip line deployed in case the anchor gets snagged.

Trip buoys are almost never over the anchor

[goboatingnow]

Originally Posted by muttnik

Interesting thread which has made me revisit my oft-pondered thoughts on how I'd implement an anchor alarm. The "where exactly *is* the anchor?" question is a knotty one. Do please be brutal if I've missed something and am stating the obvious. This is also just musings so criticism will not be taken personally :-)

I *think* from the above your second button press is purely to determine swinging radius. However the centre of that radius won't be at the drop point. Not only will current (or engine) move you as the anchor goes down, the bow will inevitably blow off. More importantly, the anchor may take some distance to dig in. When I first thought about this I thought about a manual correction but the desire to do this with button presses is laudable. Chain counter / GPS / sensor location / heading / depth info could be combined to calculate where the anchor hits bottom but that's not necessarily where it digs in.

If digging in the anchor under power, might all the parameters be obtained from the second button press alone? ie if the chain goes roughly straight when digging in under power, combining GPS, heading, depth, chain length and corrections for catenary, bow height, distance of bow roller to the chain sensor you have a reasonable idea of both centre and radius of your swinging circle. Building chain counter functionality with the arduino would be no bad thing and allow for automatic recalculation of swinging circle if you let out more chain after digging in.

Obviously this approach doesn't work if you're anchoring under sail without sufficient wind or current to make the chain go straight.

Good points , let’s see if we can invent sone work arounds

In theory knowing depth and catenary length , heading it would be possible to back validate the actual final resting point ,however I suspect catenary issues , measurement errors and so forth would generate sufficient errors comparable with dead reckoning the anchor from a know drop point. ( not to mention I don’t have electronic chain counting )

Hence I think deducing the anchor drop from (a)simply compensating for gps offset , as in most cases I’m moving slowly back when I let go the chain so the heading to the anchor point is actually can be guesstimated I suspect.

The drag issue is a good one , the best I can think of is a compensation distance set in a menu. This could be tweaked afterwards.

I think perfect is the enemy of good. I’ll have a prototype ( without heading ) to test later in the summer so it will be interesting to see how it all pans out.

[noelex 77]

Originally Posted by muttnik

More importantly, the anchor may take some distance to dig in.

It is a good point, but modern anchors set remarkably quickly in reasonable substrates. Less than 1m is not unusual so normally this is a factor that can be ignored. In very soft substrates it can take a little longer, but this is easily compensated by reducing the distance forward you place the drop point to less than the distance between the bow and GPS antenna by the appropriate amount if you feel this is likely.

The final check is that, as the boat swings, the arc drawn should be concentric with the alarm radius provided the wind is strong enough to stretch the rode back.