Miscellaneous                                                                                                             
Anchors
I am owner of an Island Gypsy 44 ( 38,000 lbs ). I am looking for
recommendation in terms of anchor. Could anyone tell me what the best
could be for such a boat?

Thank you.

Patrick Lorrain
M/V Ursule
Antibes, France



Patrick, I am still wrestling with the same question for my yet to be delivered Krogen 39.  
It is 35,000 pounds and has a frontal area of about 160 square feet so it is probably a
little smaller then yours but in the same ballpark.  I will give you my opinion but your are
not going to like it.  

Use the biggest anchor and rode that will comfortably fit on your bow.  Either use nylon
rope rode or make and use a couple of good snubbers to ameliorate the shock loads of
an all chain rode.  (See
Snubbers.)

That's the bottom line.  If you want to start at the top, it goes like this.  The force on the
anchor line is given by Skene as f(# / sq ft) = 0.0053 V^2 where V is the wind velocity in
knots.  So, for 160 sq ft, the force due to a 30 knot wind is F = 0.005 x 30 x 30 x 160 =
720 #.  But this number does not account for the shock loads due to waves or wind
gusts nor does it include a safety factor nor does it consider the forces, be they plus or
minus, due to the boat sailing on its anchor.  However, the American Boat and Yacht
Council says that the wind load on the average 40 ft boat will be 1200# in 30 kn winds,
and that this number does not include a safety factor, and anchor systems must be
designed for a force larger then that quoted.  Why the deference between the numbers,
I don't know, maybe to account for waves.  So lets use the ABYC number and throw in a
50% safety factor.  (You don't like 50%?  OK pick a number, but remember, you want to
be able to close your eyes and go to sleep at night.)  Don't get too discouraged yet, for
there are still more inconsistencies and semi arbitrary decisions to be made.  

So, what wind strength do you wand to design for?  30 kn is common for weekenders
but not world cruisers.  How about 40?  Why not 60?  Or more?  You have to draw the
line somewhere. Consider 42 kn for an every-day working anchor.  The ABYC number
for this wind is 2400#, or 3600# with a 50% safety factor.  The comparable high tensile
chain is 5/16" with a working load of 3900# and a breaking strength of 11600# and its
comparable rope is 5/8" with a breaking strength of 12200#.  On the other hand, you
could go up one size to 3/8" hi test chain (5400# / 16200# with ¾" rope (16700#) and
that would buy you a few more knots (60kn winds give 7200# anchor loads, with a 50%
safety factor included.)  

Now all you have to do is decide on an anchor.  I don't want to get into the details about
various bottom conditions or the pros and cons of various anchors or the scaling of test
data from one anchor size to another.  Suffice it to say that most anchors do not do well
in all bottoms, some anchors don't do well in any kind of bottom, there are lots of
opinions and little hard comparative test data, and the data does not support many of
the opinions and advertised performance.   Also note that most manufacturers base
their anchor recommendations on 30 kn winds.  There have been numerous excellent
letters to the list that you could refer to for guidance.  There is also the Puget Sound
anchor tests reported in the Practical Sailor.

If you were to decide on a CQR, as most world cruisers do, so I am told, all I can tell you
is that a 45# CQR will not do for 42 Knots.  The best it did in the Puget Sound tests was
1463# in mud and 1450# in sand, a bit short of the desired 3600#.  In fact it wont even
do for 30 knots of wind either, which requires 1800# of holding power for a 40 footer.  
Maybe the 60 pounder will work but will it fit on your bow?

So what type of bottom do you want to set your anchor in?

Good luck

Nick


p.s. 8-15-06:
I ended up with two approximately 45# concave anchors on my bow.  One is a Super
Max that is super in sand and softer bottoms, and the other is a Spade that is super in
sand, grass and harder bottoms.  I am very pleased with this combination.  The chain is
300 feet of 3/8 inch Hi Test.  The snubbers are 25 feet of 1/2, 5/8, and 3/4 inch
stranded nylon.