High-tech anchor watch

When forced to anchor in a spot with poor holding ground, the wind howling, the current running and a lee shore eager to snap up your boat, standing anchor watch can be a trying experience. Even in conditions less severe, the sheer uncertainty of the situation can induce a corrosive paranoia.

“Are we dragging?” you ask. A check with a hand-bearing compass reveals that the boat hasn’t moved. “No, no we’re fine.” You exhale. Fifteen minutes later, doubt resurfaces. “Are we dragging?”

Thanks to marine electronics, the anchor watch is no longer locked into this subjective loop. And now there is even a product dedicated to monitoring the status of your anchor.

A long time ago the standard way to do anchor watch was to use a “hockey puck” bearing compass to determine if the boat had moved. This involved taking bearings on fixed points and noting those in the log. As night fell and those marks became difficult to see, you often had to take new bearings on lights as they winked on ashore. When radar became a more prevalent feature on voyaging boats, you could use radar ranges on prominent land features to triangulate the boat’s position on the chart. While an easier method than taking bearings, radars do use electricity, and most voyagers are ever-concerned about conserving battery power.

Now, however, an anchor watch is far less stressful and indeed isn’t even as much of a watch as it used to be. The impressive accuracy of GPS &mdash especially GPS receivers that are equipped to use the FAA’s Wide Area Augmentation System &mdash has made anchor watch more akin to the function of a smoke detector. Set it and forget it. If your anchor drags, the GPS receiver notes the change in position and sets off an alarm. It would seem that the WAAS GPS receiver could well be the ultimate solution in the long, proud tradition of the anchor watch.

But there is a company offering yet another ingenious electronic device for standing a hands-off anchor watch. The Anchor Alert system from Deep Blue Marine, engineered by Ascend Marine, is designed to detect movement of the anchor and sound an alarm. Anchor Alert has three components: a transponder that connects directly to the anchor, a hull-mounted (or hung over the side) transducer and a display unit that has an audio alarm for waking you up.

Inside the bronze-alloy anchor transponder is a plastic cylinder that contains a circuit board. One of the electronic components on the board is something called an accelerometer. This small electronic device senses movement in both the vertical and horizontal planes. According to Wayne Prichard, president of Ascend Marine, the accelerometer has been programmed to respond primarily to horizontal movement. Should the anchor drag, the motion is picked up. “The accelerometer has the ability to sense a movement,” Prichard said. The unit “then takes a snapshot that lasts 1 1/2 to two seconds to analyze that movement and send a severity score to the display unit.” This information is transmitted ultrasonically through the water to the boat.

“This was a difficult product from an engineering standpoint,” Prichard said. One of the challenges involved getting the signal from the anchor transponder to the boat. The data needed to be received even in cases where the signal was bouncing off the bottom or off other boat hulls, creating something called multipath. “We needed to do a good job of rejecting multipath signals and noise, and get the pertinent data through,” Prichard said. Ascend engineers did this by using a spread-spectrum technique similar to code division multiple access (CDMA), the modulation scheme employed by some cell phones that allows many users to transmit the same frequency (GPS also uses a CDMA approach). Each Anchor Alert system transmits its data in a specific code. This allows the unit on the boat to reject signals that don’t match the code sequence.

Anchor Alert uses an LCD screen on the boat to indicate to users, via a bar graph, the amount of anchor movement. The unit has a user-settable alarm threshold. According to Prichard, the Anchor Alert system is superior to relying on the anchor-watch function of GPS receivers, because GPS monitors boat movement, not anchor movement. Should the boat swing into a new position due to wind and/or current changes, a GPS-based alarm might be set off, even though there may have been little or no movement of the anchor.

The bronze anchor transponder unit, which has a breaking strength of 11,000 lbs, is powered by two D-cell batteries that will reportedly last up to 60 days. The transponder is designed to turn on automatically when immersed in water and will work in a range of water temperatures. The suggested retail price for the Anchor Alert system is $1,295.

Who would have thought while standing watch years ago with only a compass and dog-eared note pad scribbled with bearings that the process would one day be so easy?

By Ocean Navigator