How Anchoring Works

Deltaville to Langley Air Force Base – 35 nautical miles sailed

By the early morning the wind was howling from the north at 20 knots, driving our boat to the taught end of the anchor scope and putting us into 6 feet of water which is exactly the depth of our rudder, putting it in jeopardy. After repositioning and resetting the anchor we held tight for several hours then at 11:30 set off in the midst of a small craft advisory to make some miles for the day and take advantage of the strong north wind pushing us southwards. The first couple of hours were rough and rolly polly as we were taking the three to four foot waves broadside as we traveled south-east to get into the open bay and away from the shoals closer to shore. After turning south it was an easy ride, especially when the winds weakened a bit in the afternoon, and yet we saw 13 large freighters anchored in the bay, not moving, perhaps waiting out the waves. We arrived in Back River and anchored in the middle of a huge, shallow bay, just off the Langley Air Force Base (which explains all the fighter jets we’ve seen flying around).

 

Today I want to write about anchoring. We have been learning a lot about anchoring and will be learning even more in the coming months as our default plan is to anchor out every night unless we can find free dockage, reasonably priced mooring balls, or have to dock at a marina for whatever reason.

 

Anchoring a boat works like this. You start with a length of chain or rope (or sometimes a combination of both) and the entire line is called a rode. One end of the rode attaches to the boat, usually in the anchor locker which is at the bow of the boat. The other end attaches to an anchor, which usually sits in an anchor roller on the bow which allows it to easily drop down or be hauled up, but it can also be stored in the anchor locker. The anchor can either be dropped into the water manually by hand or some boats have an automated system called a windlass, which is an electric (or sometimes manual) winch with a drum that the rope or chain winds around and is driven by a chain wheel with grooves or teeth that grasp onto the rope or chain. The windlass is usually operated by push buttons at the bow of the boat, or an attached controller, or a wireless or push button unit at the helm of the boat where the steering wheel and throttle controls are.

 

The anchor itself comes in many shapes, styles and weights. You normally match the weight of the anchor to the length and weight of your boat. Heavier is better as it will provide more holding power. Anchor style is as important, or maybe even more important, than overall weight. Styles include the Plow, Bruce, Danforth, Rocna, CDQ, Mushroom, Claw, Grapnel, Delta, Kedge, and dozens of other types that have been used throughout the millennia of sailing. The best style of anchor really depends on the type of bottom you are securing too, which could be sand, clay, mud, rock, pebbles, shale, weeds, or sea grass. This is why most boats will carry one primary anchor and one or more secondary anchors of different types. SeaLight has a 25 kilogram Rocna anchor as its primary and a similar sized Danforth as a secondary.

Here's the next step in anchoring. You find a spot where you will be able to swing a 360 degree arc around the anchor without floating into shallow water or obstructions. This can be tricky in a small anchorage or one with boats already anchored. Next, you drive your boat into the wind or current then let it come to a halt and drop the anchor. You then put your boat into reverse and move backwards, away from the anchor, as you spool out your rode. As for how much rode to let out, it depends on several factors. First is anchor scope. This is the ratio of the length of an anchor line to the depth of the water, and the minimum recommended is 5 to 1, but it’s better to get to 7 to 1 if you can. This means that if you are anchoring in ten feet of water, and your bow sits five feet above the water line, you need a minimum of 15 feet drop * 5 factor = 60 feet of rode, but better to have 15 * 7 = 105 feet if there is sufficient swinging room. Boats with just rope for anchor line will usually choose for more scope, but ones with all chain may use less as the chain itself is heavy and provides downward force which helps to keep the anchor in place. This is why there are only certain locations which are good for anchoring. It can’t be too deep – for example if you are anchoring in 30 feet of water you could need 245 feet of rode, which is more than most boats would carry. You want to find a spot that has between say 7 and 15 feet of depth and a bottom type that suits your anchor style.

 

Back to the anchoring process. You’ve now dropped anchor and need to reverse as the rode plays out, and you continue until the you reach the end of the rode, it tightens, and the anchor begins to set itself into the bottom. Our Rocna is designed to burrow itself into the ground, and to do this you want to continue pulling on the anchor with the boat in reverse until it is well set. With a questionable bottom we sometimes put the motor in full reverse and pull for 30 to 60 seconds until we know the boat is not moving and the anchor is full set. The final step is to tie off the rode to the boat. Some boats with a rope for anchor line use a bow cleat. Others, like us, insert a pin into the steel anchor roller and through the chain to secure it. At that point the anchoring is complete.

 

Now what happens when the wind shifts or the tidal current shifts and moves the boat in the opposite direction of where you originally set the anchor. Well, in some cases the anchor may be dug in so deep it will hold the boat even when pulling from the other direction. But usally the anchor will pull loose then reset itself in the new direction the boat is now pulling from. This doesn’t always work so well, for example if the anchor pulls free and the bottom in the other direction is rocky or full of grass. In this case, your boat starts to slip and, if you are on the boat, you will need to pull up the anchor and reset it in the new direction, possibly in a different location. If you are not on your boat, then you might arrive back to find it gone, or in a slightly different location if it eventually sticks. We have an app we use called Aqua Maps which allows me to set an anchor alarm on my phone and stream it to Ana’s phone, so when we leave the boat we can still montor it. If the boat moves outside of a pre-set radius, then we drop our calzones or sushi or hot dogs or whatever we happen to be eating for lunch and sprint back to the dinghy so we can rescue our boat before it crashes into something or floats off into the Atlantic, destined to become a ghost ship.

 

There are some situations where you may set two anchors, for example in a very tight anchorage where you are the only boat and don’t want to swing. In this case you could set your primary anchor off the bow and a secondary anchor off the stern to hold you in place. We did exactly this back in Saugerties, New York, and it worked fine until the morning when a huge wind blew in and dislodged our stern Danforth anchor because I didn’t have enough rode out. That created some morning chaos. Another method is something called a Bahamian Moor where you are faced with a tight anchoring space and a tidal current going one way that will reverse and go the other way on the next tide shift. In this case you set your primary anchor the way you normally would, but let out twice as much rode as required. Then, drop a second anchor and let out that rode as you retrieve half the rode from your first anchor. This then gives you two anchors, one for each current, and the boat will basically stay in place.

 

That’s the story of anchoring. Actually, that's just my story on anchoring. I am no expert and there are entire books written on the practice. We’ve been getting better at it, but we still have a lot to learn, with daily opportunities to do so in the coming weeks and months.