Anchoring Part 12: What Technique To Use Where
This article gives an introduction into what anchoring technique to use where:
Tags: Anchoring, anchoring technique, bearings, Bimini Twist, chafe, chartplotter, dragging, dragging anchor, Fore and Aft, Hook, Rode, rode stretch, scope, stern anchoring, stretch, V Anchoring
November 1st, 2009 at 10:31 am
Generally a single hook is all you’ll need. Remember the KISS principle and Keep It Simple, Stupid! If you have rode, anchor and shackle of the correct type, size and weight and set them securely as I’m showing in these articles, you can sleep without worry at anchor – They’ll do their job well.
If you are in an anchorage with two directions wind is likely to come from, put a hook out in the direction in the direction of each. If you’re in a narrow canyon or place with no swing room and highly defined wind direction that shifts 180°, fore and aft is the ticket. Try not to use fore and aft too quickly because you’re awfully vulnerable to wind abeam: The boat is held perpendicular to the wind, with the following problems:
* Her greatest surface area is being pushed by the wind, making the force on the boat vastly greater than if allowed to point in the wind. This alone will almost guarantee failure: Chafe is greatly increased because the lines are not pulling forward, as designed and breaking a rode through chafe at the bow or stern becomes a serious concern.
* Her smallest dimension (beam) rides the waves, so the boat will roll like crazy.
* The anchors, at very small angles to the wind, will have an enormous force to supply the holding that is almost entirely perpendicular to the direction they are pulling in. Here’s an allegory: Let’s say you tied a rope to a doorknob in a hallway door, opening towards you and then walked ten feet down the hall, pretending to be your anchor in a fore & aft setting. A friend pushes the door open and you try to keep the door completely closed by pulling on the rope. It’s going to be almost impossible to keep the door closed: The only way to do this is to pull in the direction you want to protect the boat from, in this case, perpendicular to the hall, on the outside. In anchoring, this is done by letting the boat swing to her anchor but a fore and aft anchor setup prevents this.
If you have enough room to set enough scope in opposite directions, a Bimini Twist is excellent for minimizing swinging. It’s tempting to use when there’s not enough scope because it’s easy to only think of the swing room, so be careful to make sure you’ve really got enough scope for each rode. If you don’t, don’t use it because the place you’re trying to anchor in is just too small.
Once again, I have to stress the importance of not anchoring from the stern. With a few exceptions, boats simply are not designed to ride incoming waves from that direction and you’re risking sinking your boat with either strong wind or even moderate waves.
In strong winds, the rode will stretch, so allow for extra swing room when the wind increases. In all chain, the chain straightens and in rope/chain, the rope stretches. Expect 30% stretch for a healthy stretch. You can see this on your chartplotter or by bearings. Whenever your boat moves, confirm the move and then immediately check the anchor for dragging by holding the line ahead of the bow and trying to twist it with your hand, holding that steadily for two minutes or through two gusts or two waves. You want to feel the rope stretch with the increase force and NOT feel a shudder in the rope – With one exception, that shudder is the anchor dragging!
The one exception is the boat shuddering with the force of the wave or wind gust. You will be able to tell the difference, though and if the anchor is dragging, you will feel it drag again when extra force is put on it. If this is happening and if you have extra rode and swinging room, let out whatever scope you can. Normal scope is 7:1 for rope/chain and 4:1 for all chain and heavy weather is at least 10:1 for rope/chain and at least 7:1 for all chain. Please note this assumes you have rope and chain that are strong and heavy enough! If you’re at the end of your rode, you’re going to have to re-anchor either by placing a second anchor in a V or resetting your first. I’ll cover this in more detail in the section on heavy weather anchoring, as well as other issues.