Monday, January 18, 2010

What Kind of Anchor?

You'd think that the job of an anchor would be pretty simple - it boils down to: "Stay!"

A really big, heavy weight would work.  But it would be hard to hoist and hard to store on a boat.  So anchor designs have evolved to minimize weight, using shape as a substitute for it.  An anchor not only has to grip the bottom, it has to maintain that grip in a storm, when there will be hours of pulls and jerks on the anchor rode.  And it has to maintain that grip when the wind or the tide shifts, causing the pull to change direction, often 180°. 

Over the years, many kinds of anchors have been invented.  In the modern boating world, the variety available is wide - each type has its advocates, some of whom are almost evangelical in their zeal.  I do not want to stir up controversy, so in what follows, I am not advocating; I am describing: what has and has not worked for us, and for our neighbors.  Also, different kinds of anchors work better with different types of bottoms.  Our cruising area is mostly mud bottom, with the occasional sand, so these experiences reflect that. 

Speaking of mud, with a mud bottom, there is a minimum anchor weight.  If the anchor is not heavy enough (regardless of its shape, or the size of the boat from which it hangs), it simply will not bite effectively into the mud, no matter how clever the design.  Instead, it will skip along the bottom ineffectually, or just the tips of the flukes will catch, leaving you to think that you are hooked.  But the first time the wind comes up, it will pop out.  I have a great "I learned about sailing from that" story about one such incident (with a Danforth) that happened to us.  I suspect that that minimum weight is about 20 lb. 

Around G Dock at Shilshole, these are the types of anchor most commonly seen:

The Danforth

This is the original lightweight anchor design.  The design patent has apparently run out, since there are many "danforth-like" anchors out there now made by other manufacturers.  These bury well in sand, but if you are using one on our hard mud bottoms, be sure that it is well and truly hooked.  Also, because of the large surface area, let it hit the bottom before backing up with very much speed, or
the anchor will "fly", skipping along the bottom.

We have two of these on Eolian, one as a bower, and one stowed in the lazarette for use as a stern anchor.

This one on Ghost surely weighs way more than my 20 lb recommendation, above.  There is now a lightweight version of the lightweight Danforth, made of aluminum by Fortress.  Tho they are easy to handle on deck, beware!


On G Dock, the popularity contest appears to be a tie between the CQR and the Bruce (below) anchor.  The CQR (seen here on Irene) is a "plow" type, with a hinged shank.  The hinge allows for some change in the angle of pull without the anchor having to pull out and reset.  These anchors stow nicely on a bow roller.

We have never used one, but I think their popularity among experienced boaters speaks well for them.

The Bruce

The Bruce is our favorite - this picture is of Eolian's primary anchor.  It has never (knock wood) failed us, even when there was 30 kt blowing thru the anchorage.  They were originally designed for use to keep the North Sea oil platforms in place.  With this (66 lb) anchor and 3/8" chain rode, we use 3:1 scope under all normal conditions.  The shape of the "claw" allows the anchor to basically rotate in place when the angle of pull changes, meaning there is no reset at all when the tide changes.  It has no moving parts and stows nicely on a bow roller too.

The Navy Type

In the sizes used by pleasure craft, I cannot recommend this anchor.  (As an anchor for an aircraft carrier, at 60,000 lb, it is apparently a good fit.) We have had two boats on G Dock with this type of anchor drag and sustain damage.  Both subsequently changed out their anchors for one of the above types.

The Delta Type

I just today realized that in my original posting I had left out the third place holder in the popularity contest on G Dock: the Delta type.  These are welded up from plate  and are a plow type like the CQR, but without the hinge in the shank.

Whatever type of anchor you have, be sure to pull on it, hard, with the motor before you shut things down and break into the liquor locker or jump into the dinghy.  If you want to sleep well, you don't want to wonder if the anchor will break out should the wind pipe up.

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