Anchoring a boat is not considered an art form by many boaters, only the ones who have had regretful experiences from poor anchoring practices, or have seen the damage that a thoughtlessly dropped anchor can cause. The vast majority still give little further thought to the anchor after they say "bombs away", unless it drags.Anchoring poorly endangers not only the skipper's own boat, but also every other vessel in the harbor.
The main objectives when anchoring should be avoiding damage to the ecosystem, vessel security, and ground tackle retrieval.
Anchors come in many forms. The earliest ones were a rock and a rope. Thanks to centuries of trial and error there is now have a large and somewhat confusing selection from which to choose. Anchors fall into two basic categories, sand anchors and rock anchors. Sheer weight is another concern, especially for the person "hauling the hook". Some types can be used in sand and rock with varying degrees of success.In general, like a lot of things in life, you get what you pay for.
Sand anchors, the type most often used in the Keys.The "Danforth" or lightweight style is the most popular.Those made by the Danforth Company themselves seem to be of the best quality, those with the H (for high tensile) designation in particular.This is the type with the hinged shank and two flukes.In sand they provide great holding power for their weight (very attractive to the mate). They do have the unattractive tendency to "trip out" or break loose when the wind and or current, i.e. the direction of the load, changes and the boat swings. This is more of a concern when anchoring overnight as opposed to one dive.They do hold in rock and coral but are sometimes difficult to retrieve intact.
The "Plow" anchor is popular with sailboats and trawlers and works satisfactorily but seems to require a lot of chain on the rode.This creates problems when anchoring the vicinity of coral as the chain tends to roll and drag on the bottom and coral. Plows also seem to need to be a little bit heavier than a Danforth for adequate holding power. It is resistant to breaking loose when the boat swings. The plow is a very durable hook and can withstand being "powered up" under considerable strain.
The "Bruce" anchor is one of the more versatile types available.It was originally developed for use on oilrigs in the North Sea.It digs into the sand very well and is very resistant to breaking loose when the boat swings. The Bruce requires more "scope" than the Danforth so if you are used to a Danforth and have trouble with a Bruce do not be disappointed until you try letting out more line. The Bruce is also almost indestructible. So if it gets stuck do not worry about ruining the anchor.The Bruce is however somewhat reluctant when it comes to grass.
Then there is the "Grappling hook".It is however the hot ticket for wrecks, as it can be drug through the sand until it "finds" the wreck.When it is time to leave many boats merely power it off the wreck, sometimes bending it slightly, however they are pretty easy to bend back.They are also inexpensive so if you do ruin the occasional hook, it is no bit deal. Also a small hook holds a big boat so once it is free of the wreck the mate's job is easy.
There are a lot of other types of anchors, too many to cover, but the previously described ones cover the most popular of them.All of the anchors described also need chain, to resist abrasion and to weight the shank of the anchor down so that it lays on the bottom.If you tend to anchor in small sand holes then a short but heavy chain will keep the shank down and allow you to use less scope.
No matter what type of gear you have selected the first objective is how to make the boat stay still without smashing anything pretty or ecologically sensitive. Select an area that offers maximum shelter from wind, current, boat traffic etc. Pick a spot with swinging room in all directions. Should the wind change, your boat will swing bow to the wind or current, whichever is stronger.
The next thing to do is try to determine which way the boat will point, or lay once the anchor is set. If there are other boats anchored in the area the task will be easier. If not, the fist thing to consider is the wind.The next thing to think about is the current.Short of an educated guess the thing to do is look for a trap buoy floating, or something similar. If there is a current it will leave a wake, this will identify the direction and give an idea of the velocity. If there is nothing to tell you and you have a GPS, take the boat out of gear, drift for a minute, and let the GPS give you a course and sped.That done it is a guessing game from there.
Determine depth and bottom conditions and calculate the amount of rode you will put out. Look for a sand patch, not always an easy thing to do in the shallower depths it is a matter of looking for the lighter colored areas, in the deeper spots the color difference is more subtle but nonetheless visible.Polarized sunglasses work wonders. Once you have identified sand you should cross it with your depth sounder on.In fact when you get accustomed to using sounders you can conceivably identify sand by sounder alone. If you are towing a dinghy astern shorten up on the painter enough so that it cannot possibly reach the propeller when you are backing down.Explain to your crewmembers what is expected of them, assigning duties and deck positions as necessary. It is a good idea to establish a few simple hand signals so that the helmsman and the anchor handler can communicate without shouting back and forth to each other over the whine of the wind and the engine. Depending on who is calling the shots, the helmsman may need to communicate the commands to "let go (or retrieve) the anchor", "feed out more scope", and "snub or cleat off the anchor rode". The anchor handler needs signals to request forward, neutral, and reverse gears, as well as higher or lower RPM's.
The amount of rode that you have out (scope) when at anchor depends generally on water depth and weather conditions. The deeper the water and the more severe the weather the more rode you will put out. For recreational boaters let it suffice to say that at a minimum you should have out five to eight times (5 to 1 scope for day anchoring and 6 to 8 to 1 for overnight) the depth of the water plus the distance from the water to where the anchor will attach to the bow. For example, if you measure water depth and it shows four feet and it is three feet from the top of the water to your bow cleat you would multiply seven feet by six to eight to get the amount of rode to put out.
It is a good idea to have your anchor rode marked off in ten or twenty-foot increments to facilitate reading rode length as you feed it out. If you anticipate a blow, a ten to one scope is not too much to pay out. To the extent that harbor space permits, the heavy weather rule is the more scope the better!
Having found a sand pocket and determined by the wind, current speed and direction go to the upwind current side of the pocket from the other side, stop the boat using a little bit of reverse and lower away.Lower being a key word. If you let the anchor free fall to the bottom there is the chance of the chain fouling up in the anchor, especially with a Danforth type hook. Once the hook touches the sand help the wind and current, back the boat with the engine.By going to the far side of the sand patch so there is more sand for the rode to lay on. It also keeps the line from getting chaffed or cut./p
If other boats are anchored in the area you select, ask the boat adjacent to the spot you select what scope they have out so that you can anchor in such a manner that you will not bump into the neighboring vessel.
Anchor with the same method used by nearby boats. If they are anchored bow and stern, you should too. If they are anchored with a single anchor from the bow, do not anchor bow and stern.
Rig the anchor and rode. Check shackles to make sure they are secured with wire tied to prevent the screw shaft from opening.Lay out the amount of rode you will need on deck in such a manner it will follow the anchor into the water smoothly without tangling.Cleat off the anchor line at the point you want it to stop. (Do not forget or you will be diving for your anchor.)
With the bow to the wind or current in the spot you have selected, stop the boat and slowly start to motor back. Lower the anchor until it lies on the bottom then slowly let out the rode as the boat drifts back. Backing down slowly will assure that the chain will not foul the anchor and prevent it from digging into the bottom.
Once you have fed out about one-third to one-half of the scope with the boat still backing slowly, tighten your grip on the rode until you feel the slack taken up and the anchor tugging. Then let the line feed out a bit more, keeping a light tension on it so that the anchor is being set straight. Again, tighten your grip enough to feel the anchor tug. If your grip is not strong enough for this, pass the line under the horn of a deck cleat to make it easier to hold. Snub up firmly, but not long enough to drag the anchor along on the bottom. Just long enough to feel it tugging for a second; then ease off. Repeat this snub-and-feed pattern several times.
This gentle snubbing and feeding of the rode while backing down the boat is the surest way to make an anchor set, even in difficult holding grounds. 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 it 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 all the anchor line has been let out, back down on the anchor with engine in idle reverse to help set the anchor. (Be careful not to get the anchor line caught in your prop.)
While reversing on a set anchor, keep a hand on the anchor line, a dragging anchor will telegraph itself as it bumps along the bottom. An anchor that is set will not shake the line.
When the anchor is firmly set look around for reference points in relation to the boat. You can sight over your compass to get the bearing of two different fixed points (house, rock, tower, etc.) Unless there is a strong current the boat should be pointed pretty much upwind.If the boat turns it's beam to the wind all of the sudden you are probably dragging anchor. Sometimes the best thing to do is to let out more scope and see if that helps. Over the next hour or so, make sure those reference points are in the same place. If not you are probably dragging anchor.
There is still one more step to being certain you are securely anchored.Select a range directly abeam of you, two stationary objects, preferably ashore, which are some distance apart but more or less lined up: a dock piling with a building beyond; a pair of trees - whatever is handy. Now put the engine in reverse, giving it a few hundred RPMs above idle speed. Keeping your eye on the range abeam, you will see by its movement that the boat is beginning to make sternway as the rode stretches out. If the anchor is truly set, the boat will come to an unmistakable, abrupt halt as soon as the rode is taught. The range points will verify this by ceasing to move in relation to each other. Still watching the range, increase the reverse throttle a bit more, ensuring that the anchor will indeed hold under stress. Ease up on the throttle and let the engine idle in reverse a moment before shifting into neutral. This allows the anchor rode to relax without it springing the boat forward.
If, however, the range continues to shift while you are backing down, then the anchor is dragging. If the hook drags more than a few yards without setting, you will 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. But no matter how good your technique, some bottoms are simply poor holding and may require repeated attempts to set a hook. Occasionally, you may bring up the anchor to discover that it has fouled itself in an old car tire, beach towel or paint can in which case it never would have set nor held the boat.
If there is a possibility of inclement weather or of a wind shift that would swing the boat into danger, then setting a second bow anchor is called for. Many prudent skippers always set two anchors as a matter of course. This does not mean you have to get into the dinghy and row out to windward with an anchor and a pile of chain - something I have seen done all too often. Instead, simply determine where you want the second anchor to be and drive the boat over there. You will probably have to temporarily pay out extra line on your first anchor to do this, and take it back in once the second hook is set. Place the second anchor at an angle of 45° to 60° off the first, or else in the direction of the most likely or most threatening wind shift. Set it using the same snub-and-feed technique described above.
Placing a stern anchor, when it is called for, can be done by paying out and, afterwards, retrieving lots of extra bow anchor rode.
Begin an anchor watch. Everyone should check occasionally to make sure you are not drifting.
Retrieve the anchor by pulling or powering forward slowly until the anchor rode hangs vertically at the bow. Cleat the line as the boat moves slowly past the vertical. This will use the weight of the boat to free the anchor and protect you from being dragged over the bow. Once free, raise the anchor to the waterline. Clean if necessary and let the rode dry before stowing away.
The typical pleasure boat anchor rode is a long length of nylon line shackled to a short length of chain at the anchor end of the rode. The chain is there mostly to add weight to the shank of the anchor, helping the anchor dig into the bottom. The rope part of the rode must be nylon. Nylon line is not only strong it is also elastic. When waves roll into an anchored boat, the nylon stretches like long rubber band, preventing the destructive jerking that occurs with a less stretchy rode. Both three-strand and braided nylon ropes make excellent anchor rode. Three-strand gives greater elasticity at lower cost, but braided nylon is more flexible, making it a better choice when the rode is fed through a deck pipe for stowage.
Ground tackle - the whole anchoring system, including anchor, chain, shackles and line.Anchors also must have something to attach them to the boat. This is called the anchor rode and may consist of line, chain or a combination of both.The ground tackle needs to be of a size suitable to the vessel. As a rough guideline for boats of moderate size and displacement, the primary bow anchor ought to weigh at least 1-lb. per foot of length on deck. Bigger is better. One additional anchor, made up and ready with its rode attached, should also be carried aboard. An anchor needs to have some sturdy galvanized chain between it and the anchor line, no less than 15 or 20 ft. Again, more is better. Most experienced cruising sailors fit one of their bow anchors with an all chain rode, often using a windlass with a chain gypsy to handle it.
Rode - the length of line and or chain that attaches the anchor to the boat. Simply put, the chain lead should weigh at least as much as the anchor whose weight it is supplementing.
Scope - the angle of the rode is described in terms of water depth to rode length i.e. 3 to 1 means that the rode is three times as long as the depth of the water.Seven to one would be "more" scope or a shallower angle.The more scope the closer the shank of the anchor is to the bottom, the better it holds.
Powering - refers to a technique of freeing a stuck anchor. Take in any extra rode you can by motoring up on the anchor and then tie the line off on the cleat. Have your mate stand back and motor the boat past the anchor. The boat can put considerable strain on the anchor, more than most hooks can take so be careful.
What size rope do you need? A good rule of thumb is 1/8" of rope diameter for every 9 feet of boat length. In other words, if you have a 26-foot boat, you need 3/8" line, but you should buy 1/2" rope for a 28-footer. To determine how long your anchor rode should be, multiply the deepest water you expect to anchor in by eight. If you expect to anchor in 25' of water, you need 200' of rope.
What length of chain do you need? A good rule of thumb is the length of chain lead in feet (minimum) = (weight of anchor, lb / unit weight of chain, lb/ft) times anchor materials factor (1 for steel, 1.6 for aluminum). As an example, for a 20H Danforth Hi-Tensile anchor with a 1/2" twisted 3-strand nylon rode, you would use at least 17' of 5/16 inch proof Coil chain, weighing 1.15 pounds per foot.
In the case of a 7 pound Fortress aluminum anchor, with 1/2" twisted 3-strand nylon rode, you would use at least 11' of 5/16 Proof Coil chain (10 feet) as a chain lead.