Anchoring a boat can be intimidating, but with the right anchor and some simple techniques it can be very easy and safe. Learn how to anchor your boat in a variety of conditions below.
Choosing the anchor
The size and type of anchor you will need is primarily based on three elements: boat weight, windage and bottom condition. Each anchor manufacturer has different specifications, so it’s best too look them up individually. Before picking the size, it’s best to pick the type.
There is a new generation of anchors that are taking hold of sailors and are typified by Rocna and Manson. These new generation anchors perform well in a variety of bottom conditions But you’ll also find many sailors who swear by their older generation Bruce anchors and CQRs.
The following chart is a general guideline for how various anchors perform in different bottom conditions:
“Ankkurit Testissa” Klaus Salkola, Kippari. March 2015
“14 Ancres Sous Haute Tension” Francois-Xavier de Crecy Voile May 2012
“Anchors Aware! Anchors on Test” Professor John Knox Practical Boat Owner August 2011
“Holding Power” Bill Springer, SAIL, October 2006
“Anchoring”67th Ed. Chapman Piloting and Seamanship, 2013
“Selecting the Right Anchor” Tom Burden The West Advisor 2014
How an anchor works
An anchor is a simple device. It is designed such that the more pull force applied in line with the shank; the more the anchor seeks to embed itself in the seabed. However, it is impossible to pull an anchor laterally due to the height of water between the boat and the anchor. That’s where catenary and scope come into play.
Catenary and scope
Catenary is the name of the curve that is formed by the anchor rode between the boat and the anchor. Scope is a ratio between the depth of the anchor plus the freeboard of the vessel and how much rode is deployed. Catenary and scope are both important in determining the angle at which the anchor is pulled. The lower the angle, the better the anchor will perform.
How much scope
The more scope that is deployed, the deeper the catenary curve will be. This is important because it determines the angle of pull on the anchor and acts as extra weight and friction on the seafloor. Some cruisers choose all chain rodes for improved catenary and resistance to abrasion, but the general rule is to have at least 20′ of chain. As wind or current increase the boat will move further from the anchor, decreasing the catenary and increasing the angle of pull. In a strong windstorm, when the rode is tight and there is little to no catenary, the amount of rode deployed will determine directly the angle at which the anchor is being pulled.
Common recommendations for how much scope to let out are as follows:
3:1 for lunch stops
5:1 for mild to moderate winds
7:1 for moderate to strong winds or frequent direction changes
10+:1 for very strong winds and/or current
Setting the anchor
Our system for setting an anchor is:
- Drop anchor in an appropriate location, while drifting backwards slowly
- Place marker on GPS and Ipad anchor alarm
- Let out 3:1 scope
- Reverse slowly until anchor sets
- Increase RPM to 1800 and hold for five to ten seconds
- Let out remainder of rode, depending on the anchorage and weather conditions.
Anchoring in various conditions
Anchoring in swell can be challenging if the wind is coming from another direction. Depending on the conditions we use two techniques for anchoring in swell. Primarily we set a stern anchor to keep our bow pointed roughly 15 degrees off the swell; as we have found this to be the most comfortable position. Sometimes in less challenging conditions we will set a winch bridle.
Setting the stern anchor
There are two main ways to set the stern anchor. The first is to set the primary anchor as you normally would. Once set and the appropriate amount of scope deployed, let out another five to seven scope of rode. Reverse the boat, keeping the bow into the swell until the rode becomes taut. Drop the stern anchor and take up the five scope of bow rode. Take up the stern anchor rode until it is taut. An alternative is to take the stern anchor in the dinghy to where out 5:1 scope and then winch it taut.
Rigging a bridle
After the anchor is set, some prefer to attach the anchor rode to a bridle rather than leave it running over the bow roller. A bridle offers a sacrificial layer and reduces strain on the bow roller. It also reduces swaying and yawing and the noise of the chain.
Setting the winch bridle
Another option for anchoring in swell is to set up a winch bridle. This is accomplished by fixing a line onto the rode, using a rolling hitch, and bringing that line back to a cockpit winch. By winching in on the line, it creates a bridle that is no longer directly off the bow of the boat. This option works if the wind direction is constant, though the winch line can be adjusted as the wind shifts to keep the bow in a comfortable direction.
Two anchors to reducing yawing
In areas where the wind is shifting a lot you may want to set two bow anchors. Two anchors are set to windward approximately 22-30 degrees to either side of the bow. Setting two bow anchors is similar to setting a stern anchor, except that after setting the first anchor instead of backing up you motor upwind at a 45-60 degree angle. When you are even with the first anchor, drop the second anchor and fall back between the two, adjusting the rodes as necessary.
In areas that experience fast currents and 180 degree shifts, a common anchoring technique is called the Bahamian moor. This is more common on the east coast, but is also useful in the river bar anchorages frequent along the California, Washington and Oregon coastlines. It is the same technique as setting the stern anchor, except that instead of fixing the second anchor to a clean at the stern, both anchors are run off the bow.
Wind and current
Sometimes wind and current will work against each, causing no end of concern. In such conditions, boats, especially modern hull designs with fin keels, can move around the anchorage almost at random as they are influenced alternatively by the wind and current. In such a scenario, turning the wheel hard over to one side and locking it usually keeps the boat in a relatively stable position. It is same principle as heaving-to; the forward motion of the boat causes it to turn thereby changing the wind angle and dissipating the force.
Etiquette and safety
The three simple rules of anchoring etiquette, which will also increase safety in the anchorage, are:
- Keep as much room between yourself and other boats as is reasonably possible
- Follow the anchoring method (ie. stern anchor, Bahamian moor, etc.) of the boats that were there before you
- Leave room for other boats who come after you to anchor in the anchorage
In the unlikely and unfortunate event that the anchor drags there are a number of alarms that will let you know. Some GPS chartplotters have built-in anchor alarms, drift alarms or depth alarms. These are handy, but the GPS is often in the cockpit and unless you have a receiver, you may not hear it from the V-berth. Another option is to download an anchor alarm app for android or Ipad, like Drag Queen. It has more functions than the GPS alarm and we can keep the Ipad near us at all times.
Set it and forget it
Whether you are headed out for the day, weekend or season, the basic techniques for anchoring do not change much. The vast majority of the time you will be relying on only one or two of the techniques outlined above. Anchoring is an individualistic activity and everybody has their own personal preferences that have been refined over time. But at its heart anchoring is pretty routine and doesn’t have to be overly complicated. So set the anchor, grab a drink and enjoy life on the hook.