No matter how many times we do it, setting out more than one anchor never gets easier; it is always harder, heavier, and often wetter work than we enjoy. But the benefits are undisputed. In fact, there are times when nothing else will do.
Unfortunately, the practice of laying out more than one anchor often goes underutilized. This may stem from complacency, possibly from a lack of knowledge or maybe from the lack of having the necessary equipment on board. But no matter the reason, as many crews discover, Mother Nature cares little for excuses.
Although a multiple-anchor mooring can be set permanently, if it is to be taken up and carried on board the vessel, the gear needs to be of such size that it is capable of being handled by the crew while still being big enough to hold the boat. Some crews, when trying to keep their anchors to an easily manageable size, choose small anchors, expecting that using two small anchors would work just as well as one "big enough" anchor. Except possibly when the anchors are used in tandem, this is a mistake. There will be times when the entire load is directed onto only one of the anchors, and if that anchor is too small to hold the boat, it is vulnerable to tripping or dragging, possibly going on to foul the other anchor. Because of this concern, it is important that each anchor in a multiple-anchor moor should be of a size that will, on its own, be capable of holding the boat in the worst conditions that will occur.
Choosing inadequately sized anchors is a much-too-common occurrence and we suspect another reason: that the charts that are published for matching anchor size to boat size are misunderstood. Although there are exceptions, most of these charts are usually based on wind speeds of less than 30 knots, anchorages with some protection from seas, and firm bottom conditions. Two exceptions are the Bruce anchor, which is based on wind speed of 40 knots, and the Rocna anchor, based on wind speed of 50 knots. This disclaimer, the information which is critical to be aware of when sizing anchors, is often missing. When present, it is usually in very small type, making it easy to overlook or ignore. If present, this disclaimer gives little, if any, help for choosing anchors for conditions that exceed the chart's parameters.
Over the years it has become evident to us that anchors should be at least one size larger than what is called for in the charts under certain conditions: 1) if the boat will be anchored, 2) in winds that exceed 30 knots, 3) in a bottom that is less than firm, 4) if fetch exceeds ¼ mile, or 5) if the crew plans to be asleep, ashore, or otherwise indisposed (which renders them unable to change up to a larger anchor in a timely manner should stronger winds arrive).
For storm conditions (45/75-knot winds), an anchor at least two sizes bigger than what is called for in these charts should be chosen. (The three-piece Luke anchor is an exception; when used as a storm anchor, the manufacturer recommends at least 2 lb. of anchor per foot of boat.)
Multihulls should use anchors sized to be at least 150 percent larger than what is mentioned above. For hurricanes, even when there is some protection from the seas, any boat would be better served if the anchors were even bigger.
We occasionally hear the statement, "In an emergency, anything is better than nothing," from crews that struggle with gear that is inadequate for the conditions. But to us, squalls, gales, storms, and hurricanes do not rate "emergency" status. Since this type of weather, though undesired, occurs, it should have been taken into account when sizing something as important as ground tackle.
To avoid the mistake of being ill-prepared for anchoring, the first anchor aboard should be sized for the heaviest weather that can be encountered. Only then, after this gear is on board, should the ground tackle for more typical conditions, or for convenience, be chosen. If you must err when choosing anchors, err on the "too big" side!
Keep in mind that anchor size alone is not the only important factor that needs to be addressed when anchoring. In addition to size, anchor design, scope, and the strength of all of the components are of equal importance. Each of these features performs different functions; functions that cannot be substituted one for another. If the attempt is made to substitute one feature for another, the ground tackle may, and often does, fail to perform as required.
When Two Is Better Than One
There are a couple of situations that stand out in our minds where setting a second, or even a third anchor can save a crew or a boat from trouble-sometimes disastrous trouble. One situation is when the wind or current changes direction. In this situation, laying out another anchor (one that is positioned to handle the load when the direction of the wind or current changes) is a good preemptive tactic. The other situation is when one anchor lacks the strength to resist the wind speed or seas that might otherwise bend or break it. In a situation like this, the solution may be a larger anchor or a different anchor, one of a stronger design. But another option could be the use of multiple anchors, which should be laid out in such a manner that no one anchor receives an amount of loading that could result in it bending or breaking.
These situations are not the only reasons for employing more than one anchor. Others include: providing a back-up anchor, particularly in heavy weather; tethering a boat in a location that has limited room; minimizing the amount of "horsing" or yawing the boat may undergo; laying better to the wind or current; or, holding the boat in a particular position for work to be done... and certainly there are others.
Many times it is obvious that more than one anchor should be deployed, but other times, the thought to put out another anchor is just a niggling subconscious feeling. If the situation is not clear as to when to set out additional anchors, a good rule of thumb to follow is the same rule that is used when deciding to put a reef in the sail: "If you are wondering if you should, you probably ought to."
Setting Multiple Anchors
When a crew needs to set out more than one anchor, there are three basic patterns from which to chose, although within these patterns, there is usually wide latitude where the anchors can be placed.
One pattern consists of two anchors laid out in such a way that the two rodes form an angle of less than 180 degrees. This pattern is useful when the change in the direction of the wind or current remains less than 180 degrees.
Another pattern has two anchors laid out in a straight line, but 180 degrees to one another. This pattern is usually the choice when the wind or current changes to a reciprocal course.
The third pattern has three (or more) anchors laid out in a clock-like pattern and works well if direction of the wind or current will veer or back more than 180 degrees. With this pattern, the angles between the rodes are usually made as close to equal as possible, but these angles can vary depending on the circumstances.
So how do you get those additional anchors out there? One option is to advance, veer, or retard the mothership in whatever manner is necessary to deploy the anchors. But with this method, the crew must remain alert to avoid wrapping a rode around the prop; plus, there is the added disadvantage that the vessel's maneuverability is often compromised once the first anchor is down.
Another option is to use the dinghy to row or motor the anchor out; and, if one dinghy is inadequate to defy the elements, two or more dinghies (in tandem or side by side) might be effective. When using the dinghy, place the anchor and the rode in it, while keeping the bitter end of the rode secured to the boat. Then take out the entire mass, letting the rode out as you go until that special spot is reached; then lower the anchor. Once back on board, take up on the rode to set the anchor as best as can be done.
It is also possible to lay out the gear in the reverse order from the above. To do so, take both the anchor and the rode out in the dinghy, lower the anchor at that special spot, and then allow the rode to render out during the trip back to the boat, keeping the rode's bitter end secured to the dinghy (or to a float) until ready to transfer it to the boat. (An extra section of rode, or two, can be in the dinghy in case the distance was misjudged and the rode comes up short.)
While in a dinghy, which may very well be out of balance due to the heavy gear or rough seas, the crew, especially if suited up in heavy clothing or foul weather gear, may want to consider wearing a PFD, as it may provide them their only means of flotation should a capsize occur.
When conditions become severe to the extent that it is no longer safe, or even possible, to employ any of the above, the crew will have to resort to swimming out the anchors. This is when the mask, snorkel, and fins that had been recreational gear become survival gear. In addition, if the water is cold, a wet suit may be advantageous.
In addition to the above, to swim an anchor out the crew needs items available with sufficient buoyancy, such as fenders, PFDs, cushions, or if its windage can be overcome, even the dinghy, that either individually or en mass can float the largest anchor and its rode high enough off the bottom (inches is all that is needed) so that a swimmer can tow them into position. Once the anchor is in position, releasing the anchor and its rode is made easier if a slip knot is used, although a sharp knife can always be employed.
After the anchors are set, the next chore is to secure the rode(s) to the boat. Here, too, there are several options.
One option is to bring each of the rodes to the boat, securing them together or separately at the bow, aft, or possibly amidships, wherever is best for the circumstances. The down side of belaying the rodes close together is that they can twist around one another necessitating at some point attention to undoing this twisting. Another disadvantage to securing more than one individual rode to the boat is that the lazy rode may foul on the boat.
Another option is to secure the rodes together at a common point, such as a large ring or shackle (or tie or splice them together). From this point, a pennant is shackled, bent, or spliced on and brought to the boat. Adding a second pennant, as a back up, especially if the conditions are harsh, is a good idea in case the primary pennant should part.
An advantage of running the rodes to a common point is that a swivel can be inserted between the rodes and the pennant, eliminating any propensity of the rodes to twist about one another.
Regardless of how the rodes are made fast to the boat, thought must also be given to chafe protection, and as the conditions worsen, the more vital this matter becomes. Also, when we deploy more than one anchor, we calculate the scope for each anchor the same as what is required for a single anchor.
No matter how many anchors are used, all of the "hard" gear, including the anchors, must be sized so that each has the strength to withstand not only the force of the highest wind speeds encountered, but also any surge loads (wind force x 2); plus, a healthy safety factor (wind force + surge loads x a minimum of 2). If side loading is expected, this final figure then needs to be at least doubled for the gear that will experience it.
The charts (or formulas) needed for calculating the wind's force on a boat at various wind speeds are available in books (such as The Complete Book of Anchoring and Mooring by Earl Hinz) from the American Boat and Yacht Council (ABYC), from companies that manufacture anchors, or from boat designers and naval architects.
However, rope rodes, which should be made from three-strand nylon rope, need to be sized differently than the hard gear, since stretch, chafe, and melting are factors that become involved. We size our rope rodes (snubbers and docklines, too) so that the total load (wind force + surge load) on the rode does not exceed 15 percent of the rope's tensile strength. This means that our lines that are used for mild weather are replaced with heftier lines, if the weather will deteriorate. If unsure, we automatically use our heftier lines.
When compared to a rode that is loaded above 15 percent, we find that a rode sized to remain loaded below 15 percent of its tensile strength exhibits greater strength, a reduction in excessive stretch, less chafe and melting, and a longer lifespan-all while still retaining sufficient stretch to cushion shock-loads.
Over the years we have noticed that if the "big four" (anchor size, anchor design, scope, and strength) are chosen to exceed that which is required for the wind speed, seas, and the type of bottom encountered, anchoring problems will, if not disappear completely, at least be drastically reduced.