More on Anchors and Sizing

radar image, Prideaux Bay, British Columbia

This is a radar image of one of the anchorages we’ve visited in British Columbia’s Desolation Sound. The radar is on quarter mile range, so each range ring is 300 feet (90 meters). We’re in the center of the image. There are 36 boats showing radar return!


We are surrounded by a lot of 40- to 50-foot (12- to 15-meter) yachts. The water is 55 feet (17m) deep at half tide. We set our big ROCNA anchor on 2.5-1 scope, and then, with a firm bite established, shortened the chain rode to 100 feet (30m). A scope of 1.6-1. If you calculate the angle off the bottom, combine the chain length with Wind Horse’s length, we need about 150 feet (45m) of swinging room.

Compare this to a 40-foot (12m) yacht anchored with a normal sized anchor. They will need at least 4-1 and probably 5-1 scope. Take their length and add it to 240 feet (74m) of chain, allow for angles, and you have a swinging radius of 220 feet (67m) at a minimum. The smaller boat with its normal (undersized by our standards) anchor takes a lot more room than the bigger boat with an oversized anchor. Is there a lesson here?

Not only does this work in crowded anchorages, but it benefits you in secluded spots which might otherwise be too tight with a normal anchor.

The anchor, regardless of design, will set faster, being bigger. This means it drags less before it digs in. That reduces the risk of it fouling debris. And since you take less swinging room, the chain sweeps a much smaller area of the bottom as the boat changes position, again reducing the risk of fouling.

So, how big should your anchor be? There are no hard rules, except the old laugh rule (the anchor is not big enough until people begin to laugh at you). But in general, assuming you are using one of the new generation hooks like our ROCNA, we’d fit the following to our own boats:

  • Intermezzo (50-foot ketch) – 100 pounds
  • Intermezzo ll (62-foot cutter) – 150 pounds
  • Sundeer (67-foot ketch) – 180 pounds
  • Beowulf (78-foot ketch) – 225 pounds
  • Wind Horse (83-foot Unsailboat) – 250 pounds

OK, no more preaching about anchor size (for at least this year).

Now, about our ROCNA anchor.

After two years we continue to be impressed with its performance. Throughout a summer of anchoring mainly on rock or thin mud over rock – the norm in much of British Columbia and Alaska – we have only had one spot where we failed to get a good bite the first try.

We usually set the hook on 2.5- or 3-1 scope and then shorten down to around 2-1 depending on how much space we have (usually very limited). Our routine is to set with both engines at 1100 RPM – the equivalent of a full gale in terms of anchor load – prior to shortening scope.

Our deepest anchorage was in Penderel Sound, where we had to anchor in 150 feet (45m) and had space for just 250 feet (76m) of chain.

We have had no fouls. Not picked up a single boulder, log, or cable (so far), and have not dragged.

The only wear we have noticed is some abrasion on the “chisel point” of the anchor. That indicates to us the point is working on rock, and doing a good job of it.

We really like this anchor.

Posted by Steve Dashew  (August 20, 2007)

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