T&T: anchors

[Faure, Marin]

>If any anchor is being pulled through the bottom, without tripping or
being pulled out, it would strongly suggest that the size of the anchor
was inadequate.

I'm not sure this is necessarily the case, at least from a practical
point of view.  I have read a number of books, articles, and reviews of
anchors written by people far more experienced in using (or designing)
them than I am.  And in every case that I can recall, they include the
statement that the holding power of an anchor is not so much dependent
upon its weight as on its fluke design.  Granted, weight is a very
important factor when determining how well an anchor will penetrate a
bottom, particularly hard-packed or weedy bottoms.

But if weight was the main factor of an anchor's ability to hold, then
the Fortress would not work. However in anchoring tests the Fortress
almost always comes out at or near the top of  the list in holding
power.

Assuming fluke design is the primary determinant in the holding power of
an anchor (which I believe but others may not), then it would follow
that larger flukes will hold better.  I can't think of an argument
against this other than you can reach a point where an anchor will no
longer fit the pulpit or deck mount because of the size of the flukes.
So a practical, usable anchor for any given boat is going to be a
compromise between design, anchor size, and anchor weight.

The issue I have with the plow anchor is that its basic design is such
that it "wants" to move forward when pulled on.  It's a pointy wedge
aimed in the direction of pull.  The only thing counteracting the
tendency to move forward is the angle and curvature of the blades which
use the forward motion to force the anchor deeper into the bottom, thus
increasing the resistance to forward motion.  Obviously it works as
witness the thousands of boaters who use plow anchors like the CQR very
successfully in a variety of conditions all over the world.  But in
bottoms where the resistance to the dug-in plow is not so great, the
wedge shape of the anchor makes it a lot easier to drag it forward than
an anchor with a fluke shape that resists forward motion altogether,
like a spade-shaped anchor.

Granted, using a plow anchor with larger flukes will increase the
resistance to forward motion but where do you draw the line with respect
to practicality?  The Bruce anchor sets fast but is always rated at or
near the bottom of test results when it comes to holding power.  We had
a Bruce on our boat and it dragged enough times that we changed it for a
different type.  As I understand it the Bruce design was created to hold
North Sea oil platforms in place.  At that scale of size and weight,
they obviously work great.  So we could have used a Bruce with flukes
two, three, or four times larger than the one we had on the boat, and it
most likely would have held in the conditions where the Bruce we had
dragged.  But in addition to not stowing well--- or at all--- the weight
of a way oversize Bruce would have been prohibitive for our boat and our
windlass. Hence our search for an anchor that was sized for our boat and
windlass but had a fluke design that produced the maximum possible
resistance to forward motion regardless of the bottom type.  That's not
to say it will never drag, but I believe the chances of it dragging in
less-than-ideal conditions are more remote than a plow anchor under the
same conditions.

______________________________
C. Marin Faure
GB36-403 "La Perouse"
Bellingham, Washington