Anchoring Essentials

During my years of cruising the Pacific, I have met many long-distance cruisers lacking a good understanding of the essentials of anchoring. Over the course of a few months' stay in the Bay of Islands, New Zealand, I helped rescue no less than six sailboats that had dragged their anchors and were setting rapidly toward rocks or shore with no one on board. All were voyaging boats, some worth many hundreds of thousands of dollars, and all well worth the extra thought and preparation it would have taken to ensure that they did not wander off while their owners were ashore.

Ground tackle need not be absurdly large or complex: 99 percent of the time, I anchor my 35-foot (10.5 m.) sloop on a single 33-pound (10-kg.) anchor with 5/16-inch (8mm) chain. Heed what we consider to be "anchoring essentials," and you should enjoy many peaceful nights on the hook.

Anchor weights

Selection of a working anchor begins with a simple rule-of-thumb: Plow-type anchors (such as the CQR, Delta and Bruce) should generally weigh about 1 pound per foot (1.5 kgs./m.) of boat length. Pivoting-fluke anchors, such as the Danforth, can be slightly lighter, say 1 pound per foot (1.5 kg./m.) of waterline length. Fisherman or yachtsman anchors should be heavier, about 2 pounds per foot (3 kg./m.) of waterline length. This simple approach to anchor selection is surprisingly effective, but, whenever possible, check the results against wind loadings and actual anchor holding figures.

The loads placed on anchor and rode are a function of current, waves, and wind, with the latter being the most significant in most situations. All these loads vary with the type and size of your boat. While calculating precise wind-pressure loadings generated by various boats is laborious, good estimates of drag due to wind have been calculated for various boat lengths (see sidebar on windloading). Many anchor manufacturers and some independent sources have conducted anchor holding tests, and their figures can be compared to the loadings.

Beware, however, as anchor holding ability, and the holding figures manufacturers and others come up with, can vary dramatically with the bottom characteristics. The truth is, an anchor that may hold your boat securely in gale-force winds on a sand bottom may be all but useless in areas with rock or kelp; not surprisingly, some manufacturers don't tell you this.

Anchor arsenals

Quantity: The best way to ensure that you can anchor securely in a variety of bottom types is to carry more than one anchor. While the smallest day-sailing boats and trailer-sailors — typically using their anchors for lunch stops — can get by with one anchor, most boats should carry more.

Small coastal cruisers — say around 20 or 25 feet (6 m. to 7.5 m.) LOA — will want a minimum of one working anchor and a kedge, with the kedge a bit smaller and preferably of a different type. Many sailors choose a plow for their main anchor, and a pivoting-fluke anchor, or smaller plow of a different type, for the kedge.

Larger coastal cruisers, or small boats that venture far afield, should carry two different types of working anchors and a kedge. This ensures a remaining working anchor should the other be lost, gives a choice of anchors to use on different bottoms, and increases anchoring options in bad weather or tricky anchorages.

Type: How should you select the types of anchors you will carry? Consider where you will sail, and the bottom types you're likely to encounter.

Plow: In general, plows make effective all-around anchors, good in mud and sand; I have found the Bruce to also be quite effective in coral. Any plow is likely to have trouble getting to the bottom if there is a lot of kelp.

Fisherman: In such conditions, a fisherman anchor is probably the best choice, and these are generally good for rocky bottoms as well.

Pivoting fluke: These anchors are very effective in clean sand and hard mud bottoms, but may drag easily in soft mud, and are even worse than plows in coping with kelp. The best way to choose an anchor for your conditions is to talk to other sailors, particularly those who cruise and anchor a lot, and find out what works for them.

Storm anchor: While many long-distance cruisers carry a large storm anchor (approximately double the weight of their working anchors), in addition to two working anchors and kedge, my own approach has been to simply add a third anchor of similar size to the working anchor collection. Why? My anchors are all of different types: a fisherman, a Bruce, a CQR, and a Danforth kedge, allowing me to select a working anchor for almost any bottom. Being of similar size and strength, the rodes and shackles are interchangeable. All the anchors are easily handled — in the water, on deck or in the dinghy — and none pose the stowage problem that a 70- or 80-pound (32-kg. to 36-kg.) storm anchor would. Used in combination, these anchors will provide incredible holding power, and they can be set to hold my boat securely — even when wind clocks around quickly from different directions, as might happen during a hurricane. Finally, by placing reliance on separate anchors and rodes, I have invested in considerable chafe insurance, chafing of anchor rodes being a major cause of problems during hurricanes and severe storms.

Rodes and Gear

Having selected the anchors suitable for your boat, be sure to match them with appropriate rodes and terminal gear. The chart of projected loads is quite useful when selecting the line, chain, and shackles to use with your chosen anchor. There is no point in carrying an anchor that will provide 2,000 pounds of holding power if your rode cannot carry the strain. The chart lists actual loads, incorporating no safety factors; make sure to select equipment based on the safe working load, and not the breaking strength. Never buy shackles, swivels, or any other anchor gear, if breaking strength or safe working load figures are not available. You might save a few dollars, but buying inferior gear places your boat, and perhaps your life, at risk.

Rode: Using my own boat as an example, the anchor and rode would be selected as follows. Boat length is 35 feet (10.6 m.). According to the rule-of-thumb, working anchor (plow) weight should be 35 x 1 = 35 pounds (10.6 x 1.5 =16 kgs.). The chart shows a loading, in winds of 42 knots, of 1,800 pounds (818 kgs.). The safe working load (s.w.l.) of your rode should equal or exceed this, and indicates 5/16-inch (8mm) chain, with a s.w.l. of 1,900 pounds (864 kgs.) and/or 5/8-inch (16mm) line, whose s.w.l. is 2,440 pounds (1,109 kgs.).

Shackles and Swivels: Shackles can be the weak link; a 5/16-inch shackle has an s.w.l. of only 1,500 pounds, so a size larger (3/8-inch, 2,000-pound s.w.l.) should be used. The pin of an anchor shackle will typically fit chain one size smaller. It's good practice to fit a swivel between anchor and rode; this should also be one size larger than the chain.

Is it prudent to use the wind loading at 42 knots? What happens in a severe storm, where winds may equal or exceed 60 knots? Decide first if you may ever have to anchor in such conditions. Ocean voyagers should be prepared to cope with such conditions. Now base your decision on your anchoring strategy. If you intend to place primary reliance in storm conditions on one large anchor, the rode should definitely be sized to cope with 60-knot winds. If you will be relying on two or more anchors used in combination on separate rodes, then the rode for those anchors can be based on the lower 42-knot figures.

Chain or rope: Should you use chain or rope? Both have much to recommend them, and the decision is perhaps best based on your boat and where you cruise. Because chain is much heavier, if anchorages in your area are deep, the weight of chain these require may tip the balance to rope. In addition to its light weight, rope has the advantage of built-in elasticity, and it will absorb shock loadings from wind and waves. On the downside, rope is much more easily abraded. In addition, the scope required — the ratio of rode paid out to water depth — with rope is much greater: use 7:1 with rope, and about half that with chain.

My own solution is based on the conflicting needs of good abrasion resistance — due to the abundance of coral in South Pacific anchorages — reasonable weight (my boat is already heavily laden with cruising gear), and the ability to anchor in deep water — some anchorages in the Solomon Islands, where I cruised recently, exceed 75 feet (23 m.) in depth. I have chosen to use 160 feet (48 m.) of chain, which is spliced to 330 feet (100 m.) of rope. This means that when the water depth is 45 feet (14 m.) or less (which is most of the time) I can anchor on all chain. In deeper water, I pay out all of my chain a well as some rope.

How much rope? In light conditions, I use a length of line equal to the water depth, thus keeping the line clear of the bottom. When the wind pipes up I pay out additional scope, to equal about 5:1. In 70 feet (21 m.) of water, I pay out all the chain, adding about 70 feet of rope to this in light winds. In strong winds, I pay out 190 feet (58 m.) of rope, for a combined length of rope and chain of 350 feet (106 m.). This still leaves 140 feet (42 m.) of rope in the anchor locker should yet more scope be needed. Having a splice between chain and line means the rode can be paid out or taken in without interruption.

Second and third working anchors should typically be set up with short lengths of chain (approximately equal to the boat's waterline length) spliced or shackled to rope. For working anchors, use a length of line six to seven times as long as your boat, adding to this if anchorages in your area are deep. I use the same formula for kedge warps.

Strongpoints and Accessories

Cleats and bitts: While anchors and rode constitute the essence of your anchoring gear some additional elements are also vital. First among these are the cleats or bitts to which your rode will be secured. Always use one of the above, and never rely on your windlass to secure your anchor line or chain. Ensure that the attachment point is as strong as you can make it. If you rely on deck cleats, they should be large and bolted-through the deck with large backing plates below. The bitter end of the rode should be equally well secured, somewhere in the chain locker, preferably by a heavy lashing, which can be cut in an emergency.

Snubbers: An anchor snubber is a must for those who anchor on all chain. The function of the snubber is to ease shock loads on your rode, which can be very high when anchored in rough conditions. The snubber consists of a nylon line (equal in size to your rode) that is secured to the chain by means of a rolling-hitch or chain hook. The line should be at least 20 feet (6 m.) long. Mine is now 40 feet (12 m.), after I broke a shorter snubber while anchored off a mid-ocean reef with waves breaking over the bow. I typically pay out only 8 or 10 feet (3 m.) of line, but in rough conditions, easing out another 20 feet (6 m.) does wonders. Make sure you secure the chain to your bitts or cleats independently of the snubber, in case the latter breaks. A yacht failed to do this in Fiji when I was there, and ended up as kindling on the reef.

The rough conditions that call for use of a snubber can also have your rode jumping off the anchor roller or out of the bow chocks. This can result in damage to deck, bowsprit, and gear, as well as greatly accelerated chafe. The remedy is simple: Rollers should be fitted with bails, and chocks should be closed to ensure that the rode stays where it should. Don't forget to add some chafe protection — leather or heavy hose — at the point your line or snubber passes over the chock or through the roller.

Trip-line: A small buoy and about 70 feet (21 m.) of 6-mm line is your final piece of essential gear. This is a trip-line, which can be attached to the crown of the anchor and used to help free it should the anchor become jammed in rocks or coral. It can be left in the locker if you're sure the bottom is good mud or sand, but if there is a chance it is foul, rig the trip-line.

American Mark Smaalders, a yacht designer, and his partner Kim Des Rochers, an environmentalist specializing in Micronesian issues, are in the midst of an open-ended world cruise aboard their 35-foot wood sloop Nomad out of Honolulu, Hawaii. In the May issue, Part II will address choice of anchorage, setting and retrieving the anchor, and anchoring variations.

Wind-loading and Ground Tackle

Wind-loading varies with a boat's windage. Boats with low freeboard and cabins and single masts will have lower wind-loadings than boxy ketches or schooners. Wind pressure varies as the square of the wind speed, which is why the estimated wind loads for my 35-foot sloop jump so alarmingly with higher wind speeds: 225 pounds in a 15-knot breeze becomes 900 pounds in 30 knots of wind and 1,800 pounds when it pipes up to 42 knots.

The following chart is based on estimates of wind drag developed by the American Boat and Yacht Council; if your boat deviates considerably from the average, you may wish to adjust the figures slightly, up or down.

Anchor loadings by boat length/wind strength

Day-sailing boats and small trailer-sailors may wish to base loads on 30-knot winds, but all other cruising boats should use the 42-knot wind loadings for their working anchor. Some long-distance cruisers use the 60-knot wind figures, but I suggest using those figures only for a storm anchor — and keeping the working anchor and rode to a more manageable size.