Public Discussion Forum

For those using an anchor watch, when or where do you center the watch? Do you start your watch when the anchor hits the ground or when the boat kinda settles down? Also maybe comment on the quick math in determining the radius of the anchor watch. Thanks.

Mike Cero

M/V Sea Rose (6605)

I always use the anchor watch feature on TimeZero Pro and I really like it. I can set an alarm when the boat gets close to the anchor limit and it will say, "Anchor watch warning". And if the boat goes past the limit I can program any number of alarms, but I use the one that sounds like the submarine is about to DIVE. The anchor watch will leave "breadcrumbs" every few minutes so I can be reassured that the anchor hasn't dragged or the chain isn't wrapped on a rock or coral head, etc. While on shore I can access the anchor watch from my phone providing my Starlink is on and I have a decent phone signal. The phone app will also show the depth, wind speed and wind direction as well as the boat's distance from the anchor and position on the anchor circle. We were on shore in Maine one time when a strong front came through and the wind changed 180 degrees. It was reassuring to see the anchor had set in the new position. We didn't need to rush back to check on the boat.

I've attached a screenshot of my anchor watch. The downside is that I need to keep a monitor and computer running to run the anchor watch. But I've set up the screen to show tide, wind speed and wind direction, which is useful. I can also track other boats if they have AIS (as I did for 401(Play) on the attached screenshot) to make sure they aren't dragging.

I have set up my GPS offsets so that when I set the anchor watch position it is at the bow pulpit. I lower the anchor and tell Kelly to set the anchor just as the anchor hits the bottom. I set the circle radius by adding the amount of chain I've deployed + length of the boat and add 20%. TimeZero knows how long my boat is and will sound the alarm when the stern crosses over the threshold.

I don't think you want to wait until your boat is settled to set the anchor watch alarm because if wind or current makes you swing on your anchor you may get a false alarm. That would work well enough if you could manually change the anchor position by entering the bearing and distance.

Richard Nye

Untethered, 57-22

https://forecast.predictwind.com/tracking/display/MV_Untethered/

We use our pilothouse ipad connected to a Garmin GLO and an app named Anchor Alarm (white anchor on a red field). This allows us to link iPhones to the iPad as a repeater if we are off the boat or away from the pilot house). 

Plus one to this method. For the anchor alarm, it would be better to mark your drop spot. No math or azimuth errors. You mark exactly where that anchor is and work from a fixed known point. But then the anchor doesn’t set and you redrop. And of course forget to remark your drop spot in the process. Or it skips a couple of times and then sets. And you marked the drop, not the actual set point…. You get the idea. It’s always something.

That time already well described, where the anchor has set. The engine is in reverse. Everybody and everything has stilled. That’s when I mark the anchor. I know my scope. I know my azimuth. I feed it into Aqua Maps for the anchor alarm and then visually verify the circle looks like what I’m actually seeing. Back to neutral and onto whatever is next. As already said I really like the bread crumbs that show how the boat has been moving and the anchor holding. It’s the first thing I peek at.

Dan and Bethany Moore

Blue Phoenix - 2008 Selene 59-17

We set the position at the time the Rhode is equal to the depth

Min Radius is

Rhode

+ Tide

+ Anchor set distance ( should be same as reset in a 180 tide/current change)one of our anchors sets quickly (Rochna) and one takes about 20 ft (Mantus M2)

+Add 25 ft for the Stacked GPS errors of position of anchor and position of the boat (16 ft true error for each making the relative 24 ft) if using a tablet or phone it’s 50 ft.

+ How far we can drift before there is trouble. Typically 100-150 ft unless there there are neighbors.

Anchor Pro app on a tablet is great to estimate the drift estimate because it projects a Sat image of where the anchor is and where you are relative to the shore.

Craig W

Hull 4241 MV Loblolly

Another great tool when anchoring to check on clearances to shore or other boats is an optical range finder. You can use the rangefinder to check on dragging  or more likely when another boat anchors too close to you later in the day. I use ours in most tight anchoring situations. 

I have a useful tool that I rarely use cause my wife hates it. It’s a small buoy with a strap that spools up elastically inside and the bitter end attaches to the anchor. It has retro-reflective tape on it so easy to spot at night. Basically it floats over the top of your anchor so you can see where it is. In a really fast running current it would have a small watch circle itself just like an aid to navigation. I deploy it in a high density anchorage so no one drops their anchor right over mine. If you were truly OCD about anchor position, you could dinghy over to it at mark your position right on top of it!

Corey
Sent from my iPhone

I second everything Steve posted. Almost exactly what we do and super easy. When Anchor alarm sounds (which it has once or twice due to bad math on my part), you absolutely know it. As Corey said we also use an anchor ball float to mark position of anchor. In addition to marking anchor spot it provides a mechanism to reverse pull anchor should it ever become stuck/snagged on something eg. old abandoned cable across sea bed, rocks, etc.

We almost always mark position after drop using the laser range finder. Do a little math with amount of chain deployed (Hint spend a few moments to remark the chain in 25’ increments, It’s really worth the hassle). I also factor in 25’ extra for radius after backing down “firmly” and then watching chain and bridle drop back down. 40-50 knot blows we’ve ridden out with not a moments worry. Great comfort to watch the boat sitting inside the yellow safety circumference circle while you're onshore having lunch with family and boat is out of sight.

Any questions on Anchor Alarm use or making a anchor position ball marker just holler.

John and Gabi

Wahini’s Bight

40’ trawler #4012

Hello Mike,

To answer your question about the math… This is what I used to teach in the Coast Guard Auxiliary to Coasties and the public.

When anchoring, we essentially have a right triangle with the depth as a side of our triangle, the anchor rode as the hypotenuse, and the swing radius as another side.

Reviving some long dormant brain cells from my university days…

We can solve this using the Pythagorean Theorem which states that if we know the lengths of any two sides of a right triangle, we can find the length of the third side.

The formula is (and apologies for the poor mathematical symbology as I can’t figure out how to get this correct in this interface.):

Hypotenuse = sqrt(side^2 + side^2).

Side = sqrt(hypotenuse^2 - side^2)

For example… If we are anchoring in 40’ of water and the bow roller is 10’ above waterline… Then the depth is effectively 50’. So, we put out 150’ of rode to get 3:1. We want to know our swing radius.

We use the formula, Side = sqrt(hypotenuse^2 - side^2).

40 (depth) + 10 (height of bow roller) = 50’ for one leg of our triangle. The hypotenuse is 150’ (our rode).

Side = sqrt (150^2 – 50^2) = sqrt ((150*150) – (50*50)) = sqrt (22,500 - 2,500) = sqrt (20,000) = 141.42’

So, our swing radius is 141.42’ Not significantly different than the 150’ rode we deployed.

If we take a deeper example, say 90’ depth, 10’ bow roller height and 3:1 scope then:

Side = sqrt (300^2 – 100^2) = sqrt ((300*300) – (100*100)) = sqrt (90,000 – 10,000) = sqrt (80,000) = 282.84’

Again, the swing radius isn’t significantly different from the rode we deployed.

All the math notwithstanding, I use the rode we deploy as the swing radius when I set my anchor alarm.

I set the alarm from the pilothouse when the anchor touches bottom and adjust the alarm circle to match the amount of chain I put out plus some margin to reduce false alarms (maybe another 20%).

I hope that helps in answering the core question you asked.

The big takeaway is that at 3:1 , 4:1, or even 5:1 (for your east coasters), the depth doesn’t really matter when figuring swing radius. Just use the amount of chain you put out as an approximation.

Safe Adventuring,

Peter C. Adams

m/v Blue Redd 5726

Nice job Steve and Peter! I am not suggesting that I am on a level with either of you or Pythagoros when it comes to the math, but I use your formula when deploying rode - Rode deployed, pretty much regardless of depth give or take a little, is essentially my assumed swing radius and I add another 20 percent or so on my anchor alarm to avoid false drag alarms. I also frequently use an anchor buoy with a line attached to the front of the anchor (measured generously based upon depth where the anchor will rest) so that I, and others, know where my anchor is located on the bottom. This allows me to ensure that I am approaching the anchor head on when retrieving rode to avoid pulling the chain into my bow roller at a difficult and grating angle and discourages others from lowering anchors so that their rode crosses mine, creating the risk of entanglement. I retrieve the forward line by hand when I get to the anchor as the rode is recovered and pick the buoy up with a long boat hook,

Another benefit to the second line attached to the front of the anchor is that I can use that as a release line to hopefully pull the anchor away from a snag on a rock, stump or cable if necessary, helping me avoids an unwanted scuba dive into water that I do not want to enter (However, I have had to do that more than once also).

KISS Jack

Jack Burgess, Shangri-La 6047

Has anyone use a device where the anchor buoy has its own gps and sets an alarm if the actual anchor moves (https://mooring-solution.com/)?  Monitoring the anchor as opposed to the boat might be the most direct source of movement - if the anchor moves, the boat moves?

Roger, the Morpheis looks interesting, but it seems like it's a unnecessary expensive complication IMO. I like tracking the boat's location instead of the anchor. I have more than once had the chain rapped around a coral head, cable and rocks. I could easily tell that by the arc of the boat tracks changing to a different arc with a different center. That also gave me a clue on how to get the chain unwrapped.

Richard Nye

Untethered, 57-22

https://forecast.predictwind.com/tracking/display/MV_Untethered/

Good point. Thank you Richard. 

We follow a similar line to Jack and Peter, using the length of rode as our basis for swing circle diameter plus a safety margin. Safety margin depends on size of the anchorage, traffic density etc, but generally around 20%. We have anchored regularly for the past 10 years on Selene’s and other recreationally boats both on the East Coast and PNW/SE Alaska without incident. Professionally I anchored vessels up to 405,000tons again without issue. We use the Anchor Pro app for anchor watch, saves leaving on our electronics, I’ve found it reliable, we set anchor on the App as it touches bottom.

We do not put excessive strain on the anchor in the process, as we walk out the anchor we have slight stern way on the boat, 0.2-0.5kts, this is sufficient to set the anchor. At about 2-1 scope we stop to allow the chain to come tight, as it starts to slack we lay out more chain to our desired ratio using the current/wind to set us back. As all of our anchors are high holding power they are designed to work their way into bottom, an issue with putting excessive strain on the chain is that you pull the anchor out as opposed to allowing it to bury itself. Most of the time we see boats repositioning themselves is after they did not allow the anchor to bury itself before applying large amounts of stern force. With the chain along the seabed the anchor shank is also parallel to the seabed and as such the force is causing the flukes to dig in, when the chain is pulled tight at a higher angle the shank is also at that angle, causing the flukes to point up rather than digging in as designed.

At the end of the day you have to be comfortable with your chosen method, we all want a good nights sleep!.

Phil Davies

Asante 5334

Ex Kinship 4715

Thank you everyone for your response. You’ve given me some good ideas and thoughts. The Captain and I will discuss.

Mike Cero

M/V Sea Rose (6605)

Don’t go gettin’ yourself into trouble. I think you mean the ADMIRAL.

J

Jack Burgess, Shangri-La 6047

I fully concur with Phil