One Anchor or Two?

Chapter 5 of 10 in the Online Book Anchoring Made Easy—Vol 2, Technique

So the question is: Should you use one anchor or two, and if two, in what circumstances?

Answer: if your boat is properly set up and equipped you should almost never need to set more than one anchor. Here is why:

Two Anchors Off the Bow

OK, I admit it. We have two bow rollers on Morgan’s Cloud, and back in the bad old days when we used a CQR as our bower (primary anchor) we often, particularly when heavy weather was forecast, backed it up with another and different type of anchor set at about a 45 degree angle from the bower. And in those days it probably even made sense, since we could never be sure of either anchor, so if one did drag, maybe the other would hold. Today, it makes no sense, and here is why:

  • It is pretty much impossible to share the load equally between the two anchors even when the wind is from a constant direction, since the boat will shear back and forth, first loading one rode and then the other. Even worse, when the almost inevitable (in any blow) wind shift comes, one anchor will be taking all the load. Shared load is an illusion.
  • You can only put so much weight on the bow of your boat. And, given point one above, it makes a great deal more sense to put all of that weight into one big anchor, rather than into two smaller ones.
  • Sooner or later, your boat will make a 360 degree turn around the anchors and probably more than one. And Mr. Murphy, being the kind of guy he is, will make sure that all the turns are in the same direction. Sorting the mess out can be a pain in the neck at the best of times and downright dangerous if the wind is up when you want to leave or you need to leave the anchorage in an emergency.

There is one situation when two anchors off the bow might make sense and that is when the anchorage is too small to afford swinging room on one anchor. This is the classic Bahamian moor situation, in which the anchors are set in line with the boat equidistant between them. Use this technique if you must, but do it right, as explained in the next chapter, or you face the very real possibility of fouling a rode on the keel, rudder, or prop. Also be aware that if the wind comes from a right angle to the line of the two anchors, the loads on each will be much larger than they would be on one anchor (assuming that the rodes are quite tight).

Anchoring Bow and Stern

OK, I really don’t like this one. Here is why:

  • Assuming that the reason for so anchoring is a small anchorage, either anchor dragging will result in the boat going ashore, therefore the safety of the boat depends on the holding ability of the smallest anchor. And most of the stern anchors we see are small, sometimes laughably so.
  • The loads on the rodes and anchors of a boat moored fore and aft can be truly frightening due to the boat’s inability to swing to the wind. How much more are the loads? Matt Marsh, engineer and yacht designer has calculated that for Morgan’s Cloud the loads would be fifteen times higher when the wind is on the beam, in comparison to a boat freely swinging to the wind direction!
  • So now you have trusted your boat to an anchor that is smaller than your best bower and increased the load by a big factor. Does not seem like a good idea to me.

Better a Shorefast

In small anchorages, we generally prefer one anchor and one or more shorefasts to both of the above anchoring techniques, because:

  • The shorefast(s) can be more easily dropped (and retrieved later in the dinghy) in the event that the anchorage becomes untenable.
  • A properly rigged shorefast is, in most cases, stronger and more reliable than a light secondary anchor. (Of course this does depend on having something strong like a boulder or a big tree on the shore to tie to.)

Tandem Anchoring

OK, hold on to your hats, the fur is about to fly. Tandem anchoring, beloved of many high latitude voyagers, in which two anchors are set one behind the other on the same rode, is supposed to be the ultimate storm survival anchoring technique. And maybe it was in the days before new generation anchors. Here is why it’s not now:

  • It is very difficult to properly set both anchors. One or the other is almost certainly going to be taking the load, while the other is lying on its side not set.
  • In that inevitable wind shift we wrote about above, either the closer anchor will drag over to be in line with the bow of the boat and the further anchor, or it will stay set and not move. Either way, you are now on one anchor.
  • If you have to move while it’s still blowing, getting your tandem rig back on deck will be a manoeuvre that will range from very difficult to very dangerous.
  • We have never, in 14 years of using it from the Bahamas to Greenland, had our 120 pound SPADE drag once set. If you have a big enough new generation anchor like a SPADE or a Rocna, ultimate holding is simply no longer a problem. So why add the complication of tandem anchoring for a benefit that is an illusion?

The Two Anchor Seduction

Before you dismiss what I have written as rubbish, think really carefully about why you are anchoring with two or more anchors. Is your decision based on sound reasoning, or are you setting two anchors just because the activity itself makes you feel like you have done your best to prepare for a coming storm? I certainly know I have succumbed to this type of self-delusion.

But even if it makes you feel better, setting multiple anchors may be a poor idea. Here is an example: Some years ago we were anchored awaiting a brush from a category one hurricane with expected winds to 70-knots. Another boat our size came into the anchorage and proceeded to spend three hours laying not one, not two, but four anchors. I’m sure the skipper felt seamanlike and that he had done everything possible.

But here is the thing. Not one of that careful skipper’s anchors was a new generation design and not one was as big as the single 120 lb SPADE that we were lying to. Worse still, one was a fisherman type, which was near useless in the mud of that anchorage. I would venture to assert that all of his anchors combined would not add up to the holding power of our single big SPADE. And that assuming his anchors would share the load, which of course, as the boat sheared about and the wind shifted, they would not.

But it gets worse. That oh so careful skipper had used every anchor he had on the boat. Suppose he had to slip at the height of the blow, say due to another boat dragging down on him, or an unexpected wind shift—hurricanes can wobble at the last moment—bringing a big sea in through the anchorage entrance? What then?

On Morgan’s Cloud we only had one anchor down, but we also had two more on deck with one completely rigged and ready to drop in case we had to slip the bower and move. (One good use for a second bow roller.) Who do you think was really safer? I guess I already voted.

Big Anchor, Good

Do note that all of my arguments assume that your single anchor is a big one of the new generation. For voyaging sailboats we recommend at least one size larger than the anchor manufacturer’s recommendation (ours is two sizes larger). And if you are worried about weight on the bow, consider changing to schedule 70 chain, the weight savings of which will more than compensate for the larger anchor.

Simple is Good

Our gradual change over the last 15 years to only using one big anchor, except in very rare circumstances, is just another part of our commitment to and belief in simplicity.

Book Navigation
<< Setting The Anchor

Two Anchors Done Right >>

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