Article by Tor Pinney                                                                                                                                        Back to List of Tor's Tips

                  

ANCHOR RIGHT TO STAY PUT
© 2011 Tor Pinney - All Rights Reserved

 Anchor Positioning and Setting Techniques

 

Over the years I’ve seen a lot of boats drag anchor, usually in squalls, but sometimes in perfectly mild conditions. Anchoring poorly not only endangers your own boat, but every other vessel in the harbor. Even if your hook does usually hold, take a moment now to review these simple anchoring techniques to be sure your boat will stay where you put her, every time.

Ground Tackle

Anchors, chain, line and shackles need to be of a size suitable to the vessel. As a rough guideline for sailboats of moderate displacement, your primary bow anchor ought to weigh about 1-lb. per foot of boat length. Err on the larger side. One additional bow anchor of equal or greater weight (and preferably of a different design) should also be carried, ready to deploy with its rode attached. A third anchor plus a half-weight stern hook is normal aboard boats that cruise. Keep each rode’s bitter end secured to the vessel.

An anchor needs to have some appropriately sized galvanized chain between it and the nylon anchor line, no less than 15 or 20 ft; more is better. Most experienced cruising sailors fit at least one of their bow anchors with an all chain rode, often using a windlass with a chain gypsy to handle it. A windlass, especially an electric windlass, not only spares back muscles, but also promotes safer anchoring by encouraging the crew to re-anchor as many times as it takes to achieve a perfect set.

Preparation

As you approach an anchorage, check that the anchors you plan to use are ready to be lowered and that the rodes will run free. If you're towing a dinghy astern, shorten up on the painter so that it can't reach the propeller when you're backing down.

Explain to your crewmembers what's expected of them, assigning duties and deck positions. Establish a few simple hand signals (see illustration) so that the helmsman and the anchor handler can communicate without shouting back and forth. Depending on who's calling the shots, the helmsman may need to express commands to "let go (or retrieve) the anchor", "feed out more scope", and "snub or cleat off the rode." The anchor handler needs signals to request forward, neutral, and reverse gears, and more or less engine throttle. One husband-wife team I know even has a signal for "calm down, dear!"

Positioning

Enter the harbor slowly and observe how the boats there are anchored. Most of them may be lying to a single hook, but some might have two anchors set off the bow, or even one off the bow and one astern. Some may be riding on permanent moorings. When the wind or current shifts, these boats will all respond differently. The vessel with two bow anchors set will swing in a shorter radius than boats on a single hook.

Vessels anchored fore and aft won't swing at all. Those on permanent moorings will pivot around their bows, but move very little. In light airs, boats with all chain rodes may not swing as far or as quickly as those riding to a mostly nylon rode. You, as the newest arrival, must anchor to keep clear of vessels already there, anchoring your boat to accommodate any change in wind direction and strength. This often means imitating the anchor pattern of your neighbors, or else keeping far enough away to allow room for a different anchor plan. It's always preferable to leave extra space around your boat. Be sure you wind up no less than 3 boat lengths ahead of the nearest boat behind you. More is safer and more courteous.

Now that you’ve checked out the neighborhood, position your boat bow to the wind (or the current, if that's the stronger force), right about where you want to end up once you're anchored, roughly equidistant from your nearest neighbors. Sound the depth and be sure you'll have ample water beneath you at low tide.

Determining Scope

Next, motor slowly ahead a distance of about 7-times the depth reading you just took and take a new sounding. This number will help you determine how much anchor rode you’ll need to put out. A safe minimum anchor rode length in normal weather conditions is a 7 to 1 ratio of rode length to depth; 5 to 1 for an all chain rode. "Depth" in this case is the actual depth of the water at high tide, plus the height above the water's surface of the hawse or bow roller, the point at which the rode leaves the boat.

scope = (depth at high tide + hawse height) x 7

So if high water is 20 ft. deep, and your bow roller is 5 ft. above the water, the total “depth” is 25’. You'll want to use 175 ft. (25 ft. x 7) of line-plus-chain anchor rode in average conditions, or 125’ of all chain. Mark your anchor rodes in 20- or 25-foot increments to facilitate reading rode length as you feed it out.

If you anticipate a blow, a ten to one scope isn't too much to pay out. To the extent that harbor space permits, the heavy weather rule is the more scope the better. Putting out too little scope is one of the most common mistakes skippers make when anchoring. Later, they wonder why the boat dragged during a squall.

While still hovering above the spot where you intend to lower the anchor, look around. Don't set your anchor close alongside or close off the bows of another vessel. If you do and the wind shifts, you may swing into her, or she into you. Either way you'll be responsible for any damage, being the last to have anchored. It is usually safe, however, to set an anchor a few boat lengths astern of another boat, or off her quarter, as long as you’re both using the same anchor pattern and scope ratio. 

Note where the rodes of nearby boats are pointing. A boat may have a second anchor set off in your direction, which you could foul if you drop yours on top. If the harbor winds are light or if a tidal current is running, don't assume that everyone's anchor is positioned straight out in front of them. In such conditions anchor rodes - especially chains - may veer off in any direction on the bottom. If in doubt ask any skippers you see aboard nearby boats where their anchors lie. If the water’s clear, look and see for your self.

Setting the Hook

If everything appears to be all right, circle back around to your intended final resting spot and then drive slowly forward, approximately the distance of your pre-calculated scope. Here, stop the vessel completely with a short burst of reverse power. Do not drop the hook while the boat is still moving forward. If you do, your anchor chain will drag over the anchor when the boat drops back and may foul.

When you let go the anchor, don't allow the rode to run screaming out. Rather, lower the anchor quickly but with control, paying out the rode through gloved hands, or hand over hand, or with your windlass until you feel the anchor rest on the bottom. As the anchor is lowering, the helmsman can shift the engine into idle reverse so that the vessel just begins making sternway about the time the anchor reaches the bottom. If it's windy, leave the engine in neutral and let the boat's windage provide the backing propulsion. Pay out the rode as the boat continues to back slowly, maintaining a slight tension on it so that it lays out straight on the bottom rather than piling up. Keep the boat's reversing speed to a bare minimum.

Once you’ve fed out about half of the intended scope, with the boat still backing slowly tighten your grip on the rode until you feel the slack taken up and the anchor tug. Then let the line feed out a bit more, again keeping a light tension on it. If your grip isn't strong enough for this, pass the line under the horn of a deck cleat to make it easier to hold. Snub up firmly, not long enough to drag the anchor along on the bottom but enough to feel it tugging for a second; then ease off. Repeat this snub-and-feed pattern several times. On a larger vessel with an all chain rode and heavier ground tackle it may be necessary to use the windlass gypsy for this, alternately braking and releasing the drum.

This gentle snubbing and feeding of the rode while backing the boat is the surest way I know to make an anchor set, even in difficult holding ground, yet it is a technique that few sailors seem to appreciate. It gives the anchor an opportunity to right itself, penetrate the bottom surface, and dig in gradually. It also keeps the rode clear of most bottom debris and helps keep the vessel's bow from falling off the wind. Usually, even before the scope is completely paid out you can feel that the anchor has set.

When you've laid out the prescribed amount of scope, make fast the rode while the boat is still reversing at idle speed. If the hook has taken hold, the boat will come up short on the rode and stop, setting the anchor even more firmly. You'll feel the vessel stop backing and, in a moment, spring forward slightly on the rode.

Power-Setting

Now that the anchor seems to be set, make sure it’ll hold if the wind gets up. Select a range abeam of you, two stationary objects preferably on shore, one father away than the other but more or less lined up with each other, such as a dock piling with a building beyond, a prominent rock and a tree, or whatever's handy. With the engine in reverse, raise the throttle a few hundred RPM above idle. Keep your eyes on the range abeam. You'll see by its movement that the boat is beginning to make sternway as the rode stretches out. If the anchor is truly set, you will then feel the boat come to an abrupt halt when the rode becomes taught. The range points will verify this by ceasing to move in relation to each other. Still watching the range, increase the throttle to around half full astern, ensuring that the anchor will indeed hold under stress. After 15 or 20 seconds, ease up on the throttle and let the engine idle in reverse a few seconds before shifting into neutral. This allows the anchor rode to relax without it springing the boat forward. A prudent skipper will now repeat the power set at least one more time before cutting the engine.

If, however, the range continues to shift while you're backing down, then the anchor is dragging. If it drags more than a few yards without setting, you'll have to retrieve it and repeat the entire anchoring sequence. In harbors with rocky or grassy beds where the water is clear enough to see, it pays to visually locate clear patches on the bottom into which an anchor can be lowered to set more readily.

No matter how good your technique, some bottoms are simply poor holding and may require repeated attempts to set the hook. Failing that, try using your other bow anchor instead. It should be a different design than the primary anchor and may fare better in that particular bottom. Occasionally you may retrieve an anchor and discover that it has fouled itself in an old car tire, fish net or bucket, in which case it never would have set or held the boat.

A Few More Tricks

Whenever possible, take a look at your anchor after it is set. Following your rode from the vessel's bow, swim or dinghy over the anchor and look at it through a facemask or a glass-bottom bucket. If you're a strong swimmer you can dive down and hand set a partially set hook by forcefully jamming the point into the bottom several times. Afterwards, observe it from the surface while your mate backs down with the boat’s auxiliary engine. You'll see the anchor dig itself in deeper. This is the most foolproof method there is to ensure an anchor is set.

If because of restricted harbor space you have to anchor with a little less than optimal scope, you can enhance the holding power of your ground tackle by weighing down the anchor rode. This calls for a sizeable lead weight to be shackled loosely around the rode at the stemhead after the anchor has been set, so that it can slide down the line. Tether the weight with a retrieving line to control how far it travels, and to retrieve it before weighing anchor. Then lower the weight onto or near the harbor floor. The boat tugging on the anchor rode must overcome and lift the weight before putting any significant pulling force on the anchor itself. Even then, the initial angle of pull will be more nearly horizontal, which is what you would have accomplished had you been able to use more scope. This technique is no replacement for adequate scope in winds strong enough to straighten the weighted rode, but it may be useful for a stopover in a crowded harbor in settled weather.

If there's a possibility of inclement weather or of a wind shift that would swing the boat into danger, then a second bow anchor is called for. Many prudent skippers always set two anchors as a matter of course. This doesn't mean you have to get into the dinghy and row out with an anchor and a pile of chain, something I've often seen novices do. Instead, simply determine where you want the second anchor to be and drive your vessel over there. You'll have to temporarily pay out a bunch of extra rode on your first anchor to do this, and take it back in once the second hook is set. Place the second anchor so its rode will form an angle of around 60° from the first, or else set it in the direction of the most likely or most threatening wind shift. Use the same snub-and-feed and power set techniques described above.

What I’ve discussed here isn’t the only way to anchor a boat. Placing a stern anchor to keep a boat from swinging altogether can be done by paying out and, afterwards, retrieving lots of extra bow anchor rode, or by carrying out the half-weight stern hook in the dinghy. There’s also the Bahamian moor - 2 anchors set 180° apart for strong, reversing currents - anchoring “on the fly” - dropping a bow anchor while coasting forward, feeding out the scope and then snubbing the rode to stop the boat and set the hook - and other variations.  Still, the same principles apply.

Anchoring a boat securely is one of the most basic and most important boating skills. Practice doing it correctly, with forethought, technique, control and confidence, and we'll all sleep easier in port.

~ End ~

Back to List of Tor's Tips