I'm sure many people have already figured this out but I don't recall seeing it anyplace so I thought I'd pass it on...If you have a GPS plotter, even a really small, monochrome one without any electronic charting, you can use it to set an anchor watch. Many models have an anchor watch feature that allows you to set an alarm that goes off if you go outside a circle of a set size (you can usually select the size of the circle). The trouble with this alarm is, if it wakes you up in the middle of the night, its not immediately obvious if its because you are dragging your anchor or if the wind or tide just shifted and you're swinging safely in a new place. You can set the alarm diameter greater than your complete swining circle, but that may mean you'd drag a long ways before the thing went off. During a long night on the hook with 30 knot winds, it finally dawned on me to use the track feature of my GPS. This is the feature that plots a little line showing where you've been and it works even if you don't have an electronic chart. The default for this feature is to extend the track every time your position has changed by some fixed amount, like 0.1 NM. If you can change this so that it extends the track at a fixed time interval, like every 10 seconds, the track will nicely trace out your anchor swings. Now when the anchor alarm goes off at 2am you can look at the GPS plot and see where you are relative to the anchor swings of the last few hours and either go back to sleep or run up on deck, as appropriate. With a depth alarm and the GPS anchor alarm set, and the GPS track available for quick diagnosis, I'm beginning to get a bit more sleep on those windy nights on the hook.
- Status
Good advice
We always set the GPS alarm when at anchor. The size of the circle depends upon the conditions in the anchorage. It sometimes does go off because of a wind shift or tide change, but a quick check and reset is usually all that is required. I'd rather wake up to the alarm than the sound of rocks or another boat. We have also set our radar alarm at anchor before. The Raytheon has a setting that allows the unit to come on every so often and do a sweep. You can select the area that it looks at both from a degree setting and distance out. I like the track idea, I'll have to take a look at that next time we anchor. Might be just interesting to see how much we actually move around during the night anyway, sometimes it seems like quite a bit. Dan Jonas (S/V Feije II)
We always set the GPS alarm when at anchor. The size of the circle depends upon the conditions in the anchorage. It sometimes does go off because of a wind shift or tide change, but a quick check and reset is usually all that is required. I'd rather wake up to the alarm than the sound of rocks or another boat. We have also set our radar alarm at anchor before. The Raytheon has a setting that allows the unit to come on every so often and do a sweep. You can select the area that it looks at both from a degree setting and distance out. I like the track idea, I'll have to take a look at that next time we anchor. Might be just interesting to see how much we actually move around during the night anyway, sometimes it seems like quite a bit. Dan Jonas (S/V Feije II)
Rule of Thumb?
That is good advice. As new owners of a GPS chartplotter we are still finding out all the functions. We have been trying to set the anchor alarm and as our plotter is mounted in the cockpit, we intend to put a buzzer below. Is there a good rule of thumb to follow when entering the distance for the first time? Gary
That is good advice. As new owners of a GPS chartplotter we are still finding out all the functions. We have been trying to set the anchor alarm and as our plotter is mounted in the cockpit, we intend to put a buzzer below. Is there a good rule of thumb to follow when entering the distance for the first time? Gary
Rule of Thumb
Gary, No hard fast rule. I try to take into consideration how close other boats are, how far to the nearest rocks, etc. If you start out to low, it will let you know pretty fast, because it will be going off just from the normal wind shifts. Another alarm that can be set is a depth alarm although I've never used that one for anchoring. I'm curious how you would hook up a buzzer from the chartplotter. Dan Jonas (S/V Feije II)
Gary, No hard fast rule. I try to take into consideration how close other boats are, how far to the nearest rocks, etc. If you start out to low, it will let you know pretty fast, because it will be going off just from the normal wind shifts. Another alarm that can be set is a depth alarm although I've never used that one for anchoring. I'm curious how you would hook up a buzzer from the chartplotter. Dan Jonas (S/V Feije II)
My GPS anchor alarm...
requires a MINIMUM of 0.1nm (I think) in order to elimanate false alarms due to the GPS accuracy. I will try the track setting this weekend to see what I get overnight. Like others I don't want ot get up without cause, but it would be nice to see what the distance changes are. However, I suspect that the GPS accuracy will factory into the apparent distance covered. It may not really tell you anything additional. A radar alarm with a guard zone may be more useful- at least to stay away from other vessels. Thanks for the idea. Rich
requires a MINIMUM of 0.1nm (I think) in order to elimanate false alarms due to the GPS accuracy. I will try the track setting this weekend to see what I get overnight. Like others I don't want ot get up without cause, but it would be nice to see what the distance changes are. However, I suspect that the GPS accuracy will factory into the apparent distance covered. It may not really tell you anything additional. A radar alarm with a guard zone may be more useful- at least to stay away from other vessels. Thanks for the idea. Rich
Keep smiling
I spent a very windy night anchored off Beaver island and discoverd I could bring my garmin 176c right into the cabin by my bunk. As my boat would hunt back and forth, the track line created a smile shape, and this confirmed I was not draging anchor. When I awoke durring the night, I knew as long as the smile was symetrical everything was ok!
I spent a very windy night anchored off Beaver island and discoverd I could bring my garmin 176c right into the cabin by my bunk. As my boat would hunt back and forth, the track line created a smile shape, and this confirmed I was not draging anchor. When I awoke durring the night, I knew as long as the smile was symetrical everything was ok!
Selective Availability
Hi, Colin. The track idea is a good one! With GPS 'Selective Availability' turned off, using a GPS as anchor watch is probably a lot more realistic. We tried to use it a few years ago when SA was still on, and it was a PITA. We tried to set it at 200 feet; anchorage was 12-16 feet (tide) deep with 6/1 scope, so it should have worked even with swing. But it kept going off about once an hour due to SA variations. With SA off, the accuracy should be substantially better than 0.1 nm, and should work well even at 200 feet. Thanks for the reminder! Carl and Jule s/v 'Syzygy'
Hi, Colin. The track idea is a good one! With GPS 'Selective Availability' turned off, using a GPS as anchor watch is probably a lot more realistic. We tried to use it a few years ago when SA was still on, and it was a PITA. We tried to set it at 200 feet; anchorage was 12-16 feet (tide) deep with 6/1 scope, so it should have worked even with swing. But it kept going off about once an hour due to SA variations. With SA off, the accuracy should be substantially better than 0.1 nm, and should work well even at 200 feet. Thanks for the reminder! Carl and Jule s/v 'Syzygy'
I could'nt go to sleep without it.
I use the 176 Garmin GPS anchor alarm every time I set the anchor. To make it less likely to get an alarm due to the normal swing around the hook, I activate the alarm as soon as I start dropping the anchor. Assuming that the setting of the anchor does not take too much distance, if I set the alarm radius to ~150% of the length of chain used (to allow for GPS inaccuracy), the boat can still swing 360 degrees around the anchor without alarming. It is very reassuring to see the smiling face on the GPS track, and quite alarming when you begin to see a trace that looks like the side of a Christmas tree !!!
I use the 176 Garmin GPS anchor alarm every time I set the anchor. To make it less likely to get an alarm due to the normal swing around the hook, I activate the alarm as soon as I start dropping the anchor. Assuming that the setting of the anchor does not take too much distance, if I set the alarm radius to ~150% of the length of chain used (to allow for GPS inaccuracy), the boat can still swing 360 degrees around the anchor without alarming. It is very reassuring to see the smiling face on the GPS track, and quite alarming when you begin to see a trace that looks like the side of a Christmas tree !!!
GPS 315 alarm is too low...
Unfortunately my handheld Megellan GPS 315 has a very low volume alarm! Megellan said the volume cannot be adjusted but, he was happy to report, it does flash a message on the screen...a lot of good that does when my eyes are closed. Looks like I need a different brand of GPS if I am going to get some sleep while anchoring!
Unfortunately my handheld Megellan GPS 315 has a very low volume alarm! Megellan said the volume cannot be adjusted but, he was happy to report, it does flash a message on the screen...a lot of good that does when my eyes are closed. Looks like I need a different brand of GPS if I am going to get some sleep while anchoring!
Always use it!
We always use it. When we drop anchor we push MOB on the Garmin 76 (with WAAS). This MOB is about 35 feet away from the anchor at that point, but close enough. As we drop back, the 76 gives the distance from the MOB in feet. As we pull on the anchor to set it, we watch the distance and if it stays the same, we know we are set. It also lets you know if it draggs before setting. When the alarm sounds (usually use 0.02 km) we look at the smiley face and the distance to the MOB and wether or not the distance is increasing or not. Our new 76 really made our anchoring more enjoyable. We just ended six months and two weeks in the Abacos with only four nights spent in a marina and did not drag anchor a single time, despite some very bad weather and boats dragging all around us.
We always use it. When we drop anchor we push MOB on the Garmin 76 (with WAAS). This MOB is about 35 feet away from the anchor at that point, but close enough. As we drop back, the 76 gives the distance from the MOB in feet. As we pull on the anchor to set it, we watch the distance and if it stays the same, we know we are set. It also lets you know if it draggs before setting. When the alarm sounds (usually use 0.02 km) we look at the smiley face and the distance to the MOB and wether or not the distance is increasing or not. Our new 76 really made our anchoring more enjoyable. We just ended six months and two weeks in the Abacos with only four nights spent in a marina and did not drag anchor a single time, despite some very bad weather and boats dragging all around us.
Before GPS?
This sounds like an interesting idea, but what did you folks do before GPS? Stay up all night?
This sounds like an interesting idea, but what did you folks do before GPS? Stay up all night?
Right Anchor, Set Right
in good holding ground with a 7x scope. Then we watch a range of two vertical objects that line up ashore to make sure the anchor is holding over the hours before the sun goes down. Finally, I get up and recheck if we feel a major change in the wind or waves. I we are still worried, we will put out a second anchor at 45 degrees to the first. The GPS alarm is just one more precaution. David Lady Lillie
in good holding ground with a 7x scope. Then we watch a range of two vertical objects that line up ashore to make sure the anchor is holding over the hours before the sun goes down. Finally, I get up and recheck if we feel a major change in the wind or waves. I we are still worried, we will put out a second anchor at 45 degrees to the first. The GPS alarm is just one more precaution. David Lady Lillie
Tradition
Suggests that if there is no watch set at nite, the skipper or someone assigned to the duty get's up ever 2 hours and checks the anchor. We've always done it this way. Sounds like overkill, but I've been in the harbour at Cuttyhunk when tide and wind have shifted. We never moved but a raft of two that was downwind of us was suddenly updwind and decided to bump us in the night. They came down on us gradually and we were able to fend them off. Boy did they wake up when they heard knocking on their topsides. After re-anchoring (us and them) we rode out the night without incident. The next day, before they departed, the skipper of one of the other boats rowed over with a thank-you gift. Otherwise, As I do when we set the lunch hook, always site off of two objects on shore (if possible) and keep in mind the tide and wind speed and direction. Also, you can set a second anchor if you need. You do carry a second, don't you? Geof
Suggests that if there is no watch set at nite, the skipper or someone assigned to the duty get's up ever 2 hours and checks the anchor. We've always done it this way. Sounds like overkill, but I've been in the harbour at Cuttyhunk when tide and wind have shifted. We never moved but a raft of two that was downwind of us was suddenly updwind and decided to bump us in the night. They came down on us gradually and we were able to fend them off. Boy did they wake up when they heard knocking on their topsides. After re-anchoring (us and them) we rode out the night without incident. The next day, before they departed, the skipper of one of the other boats rowed over with a thank-you gift. Otherwise, As I do when we set the lunch hook, always site off of two objects on shore (if possible) and keep in mind the tide and wind speed and direction. Also, you can set a second anchor if you need. You do carry a second, don't you? Geof
- Status