Anchors & Anchoring: A Basic Guide


Anchors & Anchoring: A Basic Guide

Sailing catamaran anchored in a beautiful azure blue lagoon. Photo: Shunga Shanga/Pond5.Sailing catamaran anchored in a beautiful azure blue lagoon. Photo: Shunga Shanga/Pond5.

Good seamanship encompasses a broad range of skills, but one of the most important to master is good anchoring procedures. From understanding what style and size of ground tackle will suit your vessel, to gathering information which will enable you to choose a safe anchorage, to good anchoring etiquette. There are a lot of variables to consider when anchoring.

Choosing An Anchor

There are several styles of anchors on the market, but they mostly fit into three design categories: a plow, a claw and a fluke. Read a few reviews and forums and you’ll quickly discover that the boating community is heavily divided on which anchor is the best.

The purpose of an anchor is to provide enough resistance against the natural forces acting on the boat – wind, waves, and current – to keep the boat fixed and safe. To do that an anchor must penetrate the bottom and create suction. Therefore, what type of bottom you are anchoring in will determine what kind of anchor you choose. For instance, most anchors will hold well in hard sand, but few do well finding grip in loose stones or a sandy seagrass bed. Mud has great suction but is sometimes difficult to penetrate and is often just a thin layer of sediment over some other material. Mud bottoms require an anchor with lots of surface area that will dig deep.

Size Matters

The age-old question that few are willing to answer honestly, does size matter? YES! It is important to choose the correct size of anchor in relation to your vessel.

Anchors are measured in weight and potential holding power. Each manufacturer should provide a guide that matches their anchor style and weight to vessel length and/or displacement. This figure is often given as LOA (length over all) but the design of the vessel should also be considered. A full keel cruising boat is considerably heavier than a catamaran of the same length and therefore will require a different size anchor.

Duration And Usage

How long you are planning to anchor should also be considered. It you are a day sailor and only throw the hook for a few hours over lunch when everyone remains onboard than you could choose a smaller anchor. However, if you are planning on leaving the vessel unattended or are anchoring overnight, then ensuring your anchor is the proper size and style is imperative.

Most cruising sailors will carry 2 or 3 anchors, usually of various sizes and styles. This allows them to change anchor to suit variations in bottom features, set two anchors in case of very heavy weather or to set both a bow and stern anchor when conditions dictate to make things more comfortable.

We carry both a plow and a claw style anchor. We have switched back and forth over the years but have found for our boat and where we sail the claw anchor is the easiest to set and most reliable. However, we have seen just about every size, style and brand of anchor being used safely and successfully.

If you have very little experience with anchors, then I suggest doing your research before you buy. Be sure to look at the manufacturer’s specifications and suggestions for each style of anchor to see if it matches your requirements. Make sure you can physically fit the anchor on your boat. Measure the size of the shank and the width of your bow roller, check the size of your chain pipe. If you have an anchor winch check maximum load and if you don’t have an anchor winch, consider that someone is going to have to manually haul up that dead weight.

It pays check with other boaters who sail in the same area to see what they use and if they have had any troubles. As well, check with boat owners who sail a similar design or size vessel as yours. Ask about their anchoring set up and if they have anything they would change or suggest. When in doubt it is always advised to go up a size in anchor if you can fit it on your roller. After all, no one ever dragged anchor in the middle of the night because their anchor was too heavy.

Choosing An Anchor Rode, Rope Vs. Chain

The anchor is only one half of the equation when it comes to safe anchoring. How you attach the anchor to your boat is also important. This rope, or chain, or combination of both is called the anchor rode. Just as there are several variables when choosing the correct anchor so too are there several things to consider when it comes to picking the correct anchor rode.

The size of your vessel and your anchoring set up is the first thing to consider.

Onboard Anchor Storage

Many smaller vessels do not have an anchor locker big enough to accommodate chain. That is if they have an anchor locker at all. In this instance rope is the logical choice. How do you determine what kind and diameter of rope to use?

Rope used for anchor rode is generally a three-strand line made of nylon. Most boaters choose a twisted line over a braided line as twisted rope provides tremendous strength and most importantly stretch, which allows it to absorb surge loads created by wave action. As well, along with being a little cheaper than braided rope, a twisted line is very easy to splice, which makes attachment points neat and attractive. A braided line is a little easier on the hands and has a reputation for coiling better and kinking less.

The rule of thumb to determine rope diameter for an anchor rode is to allow 1/8” for every 9 foot of boat length. Using this equation, a 28-foot boat would use a ½” line. However, if your boat is full keel or tends to drift in the wind when on anchor then it is recommended to go up at least one rope size. This is equation based on calm conditions. As wind increases significantly for a long period of time so too do the forces on the vessel and therefore so should the diameter of the anchor rode.

Vessels that have the space to accommodate a chain usually choose an all chain anchor rode.

Chain is heavier and stronger than rope rode but can cost up to four times as much as rope. This initial cost gap might cause some sticker shock, but it should be remembered that chain will outlast rope on most boats. This means that over time choosing chain may work out to be the cheaper option.

Like rope chain comes in different diameters, measured by the thickness of the links. Chain also comes in various grades, which determines breaking strength and overall weight. Different grades can also have different link lengths. This means when upgrading or changing anchor chain it is important to check the new link size will fit the gypsy on the anchor windlass. Otherwise, it will also be necessary to change the gypsy to safely accommodate the new chain.

Using An Anchor Snubber

The last part of your anchoring kit if you are using a chain rode is the snubber. A snubber is a length of line, usually the same type nylon line that would be used as an anchor rode, that acts as a shock absorber. Fastened to a strong point on the bow it is then attached to the chain either by a hook or with a rolling hitch. Several feet of anchor chain are then feed out so that the snubber is taut and the chain is hanging loose. The snubber will then stretch and absorb the load of the chain, taking pressure off the winch and preventing damage, not to mention making it quieter down below.

All rope, all chain or a bit of both?

Making the choice between rope and chain when it comes to anchor rode is much like choosing an anchor. There are several variations and combinations, all of which have their pros and cons. The important thing is always to consider your vessel, when and when you’ll be anchoring.
The main drawback of a rope rode is that it is prone to chafe. This will cause problems over time, especially if regularly used in rocky areas, or where there is sharp coral. To circumvent this, many boaters add a length of chain between the anchor and the rope. This not only prevents the rope rode from dragging along the bottom, but it also adds some additional weight.

Chain is extremely abrasion resistant, but it is also heavy. Some boaters find this extra weight in the bow affects performance. Choosing a higher test chain can cut back on overall weight but will cost you.

Length: How much anchor rode is needed?

When anchoring the amount of rode paid out is based on the depth of water the vessel is anchoring in. For instance, with an all chain rode a minimum ratio of 3:1 can be used in calm weather. This means when anchoring in 10M of water 30 M of chain should be paid out. With a rope rode this ratio would be 7:1, regardless of whether a short length of chain is used on the bottom. As depth in the anchorage increases so too should the ratio of anchor rode used. At 15M using a 5:1 ratio for chain is recommended.
As well, when weather conditions deteriorate, winds and waves increase. More rode should then be paid out to counteract the forces on the vessel. Using more rode will not only to increase the weight that is holding the boat in place but makes sure that there is enough chain paid out to lie along the seafloor. This will ensure that the anchor is not mistakenly dislodged when the weight of the vessel puts the rode under tension. Therefore, you much carry enough rode to anchor safely, taking into consideration variations in depth and weather conditions.

Regardless of what style and size of anchor and what type of rode you use it MUST be attached to the vessel at the bitter end. Choose a strong point on the boat and make sure the end of the rode is secured properly. If using chain, a length of rope, long enough to exit the anchor locker and clear the winch, should be spliced to the end. This will allow the anchor to be cut free easily in case of an emergency. Fail to do this and you could lose your anchor and rode complete over the side.

Choosing An Anchorage

An ideal anchorage shields your vessel from the wind and swell, providing a calm, protected spot to stop. Therefore, one of the most important factors to consider is the direction of the wind. Both the prevailing winds for the area and the direction the winds are forecast to blow from should looked at to ensure the anchorage will be safe and comfortable throughout your stay.

For example, an anchorage may be protected from the prevailing seasonal winds, but a local system forecast to blow through from the opposite direction would make it uncomfortable and potentially dangerous. Not only would the anchorage now be open to the wind, but your vessel would be pushed towards land where, most often, the depth of water decreases rapidly and the ability to maneuver is constrained. This is called being on a lee shore and it is very treacherous.

It is also important to consult a chart to check for bottom conditions, depth and any hazards in the area. As mentioned above the best holding will be found in hard sand or mud, when using the appropriate anchor. A seafloor that is relatively flat and free from major obstructions makes it easier to find good holding. Large rocks, coral “bommies” (outcroppings) or sunken objects like wrecks should always be avoided as it is easy to foul an anchor in these conditions. Freeing a fouled anchor is not easy, even for divers, and often results in lost gear. As well, highly polluted harbors where the ground is fouled with things like plastic bags provides very, very poor holding.

The last thing to consider when anchoring is your neighbors.

There is a tendency, when anchoring, for vessels to park close to one another. Regardless of the size of the anchorage or the conditions. Whether it is FOMO or just assuming that since one boat has anchored there is must be a good spot, it is a phenomenon that I have witnessed over and over again.

Not only is it annoying when someone anchors close enough that you can hear every word they say, it can be also dangerous. For example, if a vessel at the front of the pack drags anchor they will naturally back down on vessels behind them, potentially fouling anchors or colliding. As well, if the wind drops out vessels will often swing and drift out of sync. Anchored close enough they can easily collide.

To avoid this always keep in mind the swing radius of both your vessel and neighboring vessels when anchoring. The swing radius is the total length of rode you have deployed plus the length of the vessel. Choosing a spot that is far enough away from other vessels that the swing radius circles do not overlap will ensure safety and privacy.

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