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Anchoring a multihull

2013 July 17

Master the nuances of anchoring a big cat and you'll be the envy of the charter scene

Anchoring is an essential cruising skill, and one that you'll notice not everyone has grasped if you spend a cocktail hour in a busy anchorage. Compounding the problem is that the techniques for anchoring a multihull, as many charterers prefer, are different than those used for centuries on monohulls. So even a sailor who can anchor his monohull at home with few dramatic moments can have some problems when it comes to anchoring the big cruising cat he chartered.

Setting up the boat is good place to start. You need to consider the anchor, rode, bridle and the windlass. Multihulls present interesting anchor system design constraints: The boats are light by design but the high freeboard and shallow underbody can place high loads on an anchor. Anchors are often specified by the displacement of the boat, in the case of a multihull you may need to specify an anchor a size larger than what the displacement tables dictate. You can't really have an anchor that is too big, you just need to balance size against weight. Most cruising multihulls are large enough to use a substantial amount of chain, if not an all-chain anchor rode. The chain should be sized to the anchor and windlass.

The anchor bridle is a critical component on any boat but especially on a multihull. The bridle acts as a fusible link and general connection point between the chain rode and the boat. Typically an anchor is lowered on the chain rode and then connected to the boat via rope bridle and chain hook. The bridle adds a little elasticity to the chain rode and protects the anchor windlass from being shock-loaded as the boat surges at anchor. The bridle also allows the anchor rode to lead fair to both hulls.

Typically, the windlass is on the bridgedeck right at the base of the mast, but if you anchored from this point, or lead the bridle to one hull, the boat wouldn't lay quietly at anchor. By leading to both bows using a bridle the boat lies balanced. The section of rode between the bridle attachment and the windlass is not loaded, it is just a lazy loop of chain. If you make this lazy loop long enough and let it hang down in the water maybe 10 feet, it will pull the bridle deeper underwater, slightly lengthening the scope and the loop will tend to keep the chain tightly locked into the chain hook. A great chain hook for a multihull is the Sea-Dog Chain Gripper Plate, which is set up to lead cleanly to both bows and has a wide slot to accommodate most any chain. Equally as important, when you let the load off the bridle the chain gripper will fall free. It is nice to set up the bridle in a semi-permanent fashion, just long enough to reach from the bows back to the location of the windlass on the bridgedeck. Typically a bridle is made of three-strand nylon for maximum elasticity and about the diameter of a dockline.

Anchoring any boat requires the same fundamentals: a good holding bottom, proper scope and room to swing. A good clean sand or mud bottom is your best bet for holding, but rocks or weeds can work. We all do our best to avoid coral bottoms. Consulting a chart, cruising guide or breaking out a snorkel and fins should find you a good spot. Once in a spot you need to set an anchor with at least a 5-to-1 scope, meaning that the boat's distance from the anchor needs to be five times the depth of the water. For instance, a 10-foot water depth requires a rode length of at least 50 feet. In a wind shift a boat could theoretically swing 360 degrees around the anchor and you need to be sure there is adequate depth throughout that circle.

The technique of anchoring a multihull is similar to anchoring a monohull. The approach is the first step, and you want to approach the anchoring dead slow and take a spin around the swinging circle to make sure the depth is adequate but not too deep. Look around to make sure you have plenty of space from other boats, as going bump in the night is never a pleasant awakening in an anchorage. Once you are happy, approach the area where you want to drop the anchor from downwind. Approach very slowly as you want the boat to be stopped when you drop the anchor. As the anchor hits bottom, pay out chain from the windlass and drift or slowly motor in reverse downwind. You can use the maneuverability of the twin engines to keep the boat drifting squarely downwind in reverse. Once you let out enough rode, you can hook up the bridle and stop the boat. Remember to let out a little more chain to have a loop of chain between the bridle and the boat. When the boat stops on the anchor, apply a little power in reverse to set the anchor. Have a crew person put a hand on the bridle to detect if the anchor is set. You'll feel the anchor bounce along the bottom if it's not. If it's not set, pull it up and make another approach.

There is some technique to pulling up the anchor, but it requires a lot less finesse than dropping. You want to motor up to the anchor. Remember, the windlass should not pull you there; it's meant to lift the chain and anchor into the boat and not move the boat. Slowly power up to the anchor and pull in chain as you go, as you approach the anchor stop the boat and pull the anchor up.

Communication is key in anchoring. We've all seen unhappy cruisers shouting at each other from opposite ends of the boat, but there is a better way. Hand signals are great from the helm to the bow. You can adopt your own system, but it needs to communicate stop, go, left, right, anchoring up and down. If hand signals aren't your thing, small radio headsets are a great addition.

Anchoring, done well, can be one of the most enjoyable aspects of cruising. And nothing is more impressive than a crew that swings into an anchorage and does it flawlessly.

Learn to handle a cruising cat

Cruising catamarans are some of the most popular boats in charter fleets. Their shallow draft allows sailors to explore thin-water areas without worry, their ample size ensures that everyone on board has their own space and there's a certain amount of comfort that comes with tackling a big breeze without being heeled over. But catamarans don't behave the same way monohulls do and even advanced sailors may want to gain more experience on them before taking on a bareboat charter.

Many sailing schools now offer special multihull courses. The American Sailing Association offers a Cruising Catamaran class ensuring that students who have passed the course are capable at the wheel of a big cat. The courses are offered by many ASA schools, including those that also have charter operations, making it possible for sailors to schedule the course and then lead straight into a charter.

For more on the courses and schools that offer multihull certifications, go to www.asa.com.