Anchoring Technology

Location:   Warderick Wells Cay, Exumas, Bahamas
Coordinates:   24° 23.689′ N  76° 37.950′ W

Since leaving the U.S. we have begun to anchor out more often than we moor at a marina. Anchoring is both easier on the budget, and more satisfying to the soul. However, it does not come without some concern for the security of the boat and the comfort of the crew. While I’m sure we still have a lot to learn, this entry describes some of the tools we use and lessons we’ve already learned.

We have two anchors aboard Three@Sea. Our primary anchor is a 75-pound “plow” anchor (CQR brand) with 300 feet of chain. This seems to be a great anchor: it sets quickly and allows for a wide swing angle without having to re-set. Our secondary anchor is an aluminum “danforth” with 24-inch flukes (Fortress brand), 40 feet of chain, and 250 feet of nylon line. The danforth anchor was designed to hold the landing-craft off the beach during the invasion of Normandy during WW-II, and it lives up to its design: this is a great sand anchor.

The main thing you are concerned about when anchoring is that your anchor will hold the boat in place. But even in this simple goal there are conflicting forces: A longer rode (chain and/or line) gives the anchor a better chance to hold because there is less force pulling “up”, and more force pulling “sideways”. However, the longer the rode, the wider the swinging range when the wind and/or current change. Many of the anchorages in the Bahamas have strong tidal currents, which change direction with the tidal cycles. So not only will you swing around on your anchor, but you will probably swing around 180 degrees, which may even cause your anchor to pull out backwards and have to re-set itself (which it may or may not do successfully every time). This is why somebody came up with the “Bahamian moor”.

A “Bahamian moor” uses two anchors, set at approximately 180 degrees from one another, in line with the expected current flow. When the tidal current is going one direction, the upstream anchor is active and the downstream anchor is slack; when the current switches around to the other direction, the opposite anchor takes over, leaving the previously working anchor slack. This has two main advantages. First, because each anchor is only pulling in one direction, they are likely to stay set (i.e., not pull out backwards or drag unexpectedly). Second, because the boat is connected to the end of each anchor rode where they meet halfway between the two anchors, the boat stays pretty much in one place, only rotating around the bow where it is connected to each anchor rode. This is very cool! While we won’t set a Bahamian moor every time we anchor (it’s definitely more work than setting one anchor), now that we’ve used it a couple times, I’m convinced of its usefulness.

How do we know whether we’re staying in one place or not? We use two tools for this. First, our GPS system has the ability to set an “anchor alarm”. Once it seems like our anchor is set  (which is simply judgement), we set the anchor alarm on the GPS to tell us if we have moved more than, say 60 or 120 feet (i.e., 0.01 or 0.02 nautical miles). We usually put out about 75-100 feet or anchor rode, so this size alarm will tell if we have dragged significantly, or (if we’re not on a Bahamian moor) that we have swung around to the other side of our anchor. If the anchor alarm goes off, how do we know which it is (swung or dragged)? Well, we could look at a landmark on shore, or judge the distance from other boats around us. Unfortunately, both of these are pretty subjective, and very difficult to do on a moonless night at 3am. Enter the second tool.

Both of our navigation plotters have the ability to draw a “track” of where the boat has been (based on the GPS signal). While at anchor we can zoom in to the largest magnification, and we can actually see the path of our swinging boat being drawn on the plotter. Over several hours this looks like a big blob of scribbles, which makes it very easy to see if we move outside the normal area of movement. So when the anchor alarm goes off, we turn on the plotter screen and immediately see the nature of our movement. Pretty cool!

Okay, now that the boat is secure, how do we make it more comfortable? This really boils down to reducing pitch and roll as much as possible. The first and most important thing to achieve this goal is to select an anchorage that is well-protected from the prevailing wind and sea. We do this by looking at the geography of the proposed anchorage, and being aware of the weather and currents. Most of the time you want to be on the lee (downwind) side of some land, tucked up as close as possible to the land (but far enough away so that you can still swing on our anchor and not run aground). Once this is accomplished, there will still invariably be some waves in the anchorage. The waves that come straight into the bow of the boat aren’t too much of a problem: the boat pitches a little bit, but it’s not too uncomfortable. The real problem is the roll, which can make you feel sick over a period of hours. For this problem, we deploy a “flopper-stopper”.

A flopper-stopper is essentially a lever that you put out one side of the boat to resist the roll. (What’s the quote:  ”Give me a long enough lever, and I can move the world!”) Our flopper-stopper is a 10-foot arm that sticks out the port side at about amidship. It has a chain that extends diagonally up to our stack, and a chain that hangs down into the water to attach to the “plate”.  The plate is like a check valve: when it gets pulled up by the boat rolling right, it resists against the water; when it drops down by the boat rolling left, it lets water through and sinks quickly to keep the chain taught (making it ready to resist when the roll reverses). This doesn’t take all the roll out of the movement, but it helps a lot!

Of course, none of this would work at all if I didn’t have the best crew in the world: Kathryn and Ayla have become masterful at handling the anchors, making my job of maneuvering the boat much simpler during the anchoring and un-anchoring process. The process of setting and retrieving two anchors is not easy, and it requires all three of us to do it successfully. Eventually, I expect that we’ll even do it smoothly.

7 Responses to “Anchoring Technology”

  1. Jeff I. says:

    David and family,

    Greetings from the Blue Ridge Mountains of Virginia, where the temperature last night was 9 degrees (brrrr). I imagine spending Christmas on Three@Sea there in the Exumas is very comfortable, but dramatically different for each of you. I just discovered your web site this evening when searching YouTube for “Trawler Cruising” videos. I know you are proud of Ayla, who is doing a superb job with the videos. You are all writing great entries in your blogs and it will be exciting to follow your progress.

    I am an old salt from serving in the U.S. Navy years ago and spent many memorable months in the Bahamas, Turks and Caicos, and numerous islands in the Caribbean. I am now a farm broadcaster in radio and TV (wow – what a career change), but long for those star-filled nights at sea.

    Merry Christmas to your family from ours. We’ll be following your journey closely.

    Jeff I.

  2. Jon Besemer says:

    David,

    Very interesting post. We still have problems trying to anchor in our little lake. Trying to figure out the best “method” is a science that we have yet to master! Appreciate these kinds of informational posts.

    Merry Christmas to all.

    Cousin Jon

  3. Josh P says:

    David and family,

    Ahoy! Avast! Ahhrr, me mateys! (Hey – side note: do you guys ever speak like this onboard? I know I would, until Tesa made me stop…)

    We have been monitoring your progress with much excitement and anticipation. It goes without saying that you three have taken on the adventure of a lifetime, and it’s a lot of fun to keep up with your travels and travails. Of course, as we live in landlocked Charlotte, 99% of your nautical terminology is completely alien to us, but by reading through the lines, we gather that you all are really enjoying your time at sea. ;-)

    Have a safe and happy holiday!

    Josh, Tesa, Adalind and Zy

  4. Chips Ahoy! Thanks for sharing your journey!

    Some day isle,
    Joe
    Amelia Island, Floriduh USA

  5. Steve says:

    Hi David,

    Merry Christmas to all 3 of you. We really enjoy your adventures. I especially appreciated your comments on your flopper stopper. I am thinking of upgrading the set on my trawler. Now, it has port and starboard booms with Magma, hinged plates. They do help, but I would like to improve the effect. I have a couple of questions for you, if I may. Do you think that the 10′ boom is of an aqequate length? I have read that the longer the better, up to a point of course. My booms are 8′, and I am thinking of lengthening to 10 or maybe 12′. Do you have provisions to add a second unit on the starboard side? And, would it be worth the effort / cost. I originally started with 1 unit, and after adding the second, saw some improvement. Thanks for the feedback.

  6. Greetings from Sacramento! Thank you for your posts as you advance in your adventure.

    I too have fears about anchoring and wondered a few things after reading your post. The Fortress anchor is much lighter than the plow so how does it hold up with the 40′ of rode and line? Seems like I would be a bit nervous. Then you say:
    A “Bahamian moor” uses two anchors, set at approximately 180 degrees from one another, in line with the expected current flow. When the tidal current is going one direction, the upstream anchor is active and the downstream anchor is slack; when the current switches around to the other direction, the opposite anchor takes over, leaving the previously working anchor slack. So, is the second anchor atached to your stern or is it also attached at the bow? And finally, how do you bring up the fortress, don’t you have to be right on top of it to get it up? And have you ever had an anchor get stuck?

    Thank you again and happy cruising!
    John

  7. dbesemer says:

    Hi John,

    Yes, the Fortress anchor is much lighter, primarily because it’s made of aluminum, but it’s actually larger and has more surface area than our CQR anchor. When it’s dug in, it should have more holding power than the CQR, as long as it does not bend or break. And if you ask the Fortress guys about that, they are quite confident that their anchors will not bend or break. The strength to weight ration of aluminum is quite high, so I think I can believe them.

    We attach both anchors to the bow. When the current changes, the upstream anchor takes over, and the boat swings around by the bow. My only concern with the arrangement is that the slack rode (the downstream rode) is under the boat when it’s not active. I worry that it might get snagged on our stabilizers or running gear when it goes taut, but so far that has not happened. In reality the rode is rarely exactly underneath the boat, so it just seems to work out. We’ll see…

    I think the most challenging part of the Bahamian moor is retrieving the anchors — it takes all three of us aboard Three@Sea to do it. We pull up the CQR first, which has the all-chain road. While I maneuver the boat toward the CQR, one person is pulling in (and washing) the chain, while another person is letting out rode on the Fortress anchor so that we can get closer to the CQR anchor. The key to this first maneuver is trying not to run over the rode from the second anchor while going toward the first — it’s a little tricky. Once the first anchor is out of the water everything gets easier. I swing the boat around and start heading toward the Fortress, which now has 150-200′ of rode out (because we had to let it out to get to the first anchor). My capable crew just pull it in and wash it as fast as they can. Eventually we are right over the Fortress, and it pulls right up. As I mention in my post, we don’t do this soothly yet, but we’ll get there.

    Thanks for reading!
    David

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