John Lacey,
former honorary naval architect of the Royal Naval Sailing Association, and a
member of the Royal Corps of Naval Constructors, said in the fall 1982 issue of
the RNSA Journal that until the
disaster of the 1979 Fastnet Race, few people had explored the stability
characteristics of yachts sailing on coastal waters, beyond a 90-degree
knockdown.
But on the
night of August 13, 1979, that complacency changed. Sixty-three yachts each
experienced at least one knockdown substantially farther than 90 degrees. Many
did not right themselves quickly, and remained upside down for considerable
periods.
Lacy said
the influence of the then-popular International Offshore Rule (IOR) for racing
yachts had radically changed the shape of yacht hulls by greatly increasing the
proportion of beam to length.
"Increase
of beam gives great sail-carrying power without additional ballast," he
pointed out. "It also provides the benefit of greatly increased
accommodation in a given length."
But the
shape of such a hull also makes it very stable when inverted. In other words, if it is turned upside down
by a wave, it tends to stay upside down. To bring the boat upright again would
require about half the energy needed to capsize the boat in the first place.
"Since
the initial capsize may have been caused by a once-in-a-lifetime freak wave,
one could be waiting a long time for a wave big enough to overcome this
inverted stability."
By way of
contrast, Lacey calculated that a narrower cruising hull with a lower center of
gravity, such as a Nicholson 32, would require only one-tenth of the capsize
energy to recover from a 180-degree capsize.
Beamy,
shallow-bodied boats, he said, "may increase the size of the wave needed
to initiate capsize, but in the end the sea will still win if the wave is
awkward enough. It therefore seems in my opinion that we should tackle the
problem from the other end, and design yachts for minimum stability when upside
down."
So, to
recap, here are the main requisites for fast recovery from a 180-degree capsize
in a monohull:
Ø Moderate to narrow beam
Ø A low center of
gravity (mainly from a deep, heavy,
ballast keel)
Ø A moderately high
cabin top with reasonably wide side decks, and
Ø Watertight hatches,
ports, ventilators, and cockpit lockers so little or no water gains ingress
while the boat is upside down.
Finally, I
always advise anyone contemplating taking a boat into blue water to "think
inverted." Try to imagine all the
chaos that can happen when a boat is forcibly dumped upside down. And take
steps to prevent that chaos.
Today's Thought
If the danger seems slight, then truly it is
not slight.— Francis Bacon, De Augmentis Scientarium: Principiis Obstare
Tailpiece
"Why
did that sailor buy drinks for all those girls?""He likes to have a port in every sweetheart."
(Drop by
every Monday, Wednesday, Friday for a new Mainly about Boats column.)
3 comments:
Small Boat to Freedom by John Vigor(2nd Edition,2011)
Got and read this book over the New Year. Enthralling.Could not put it down.
Should be compulsory reading for everyone contemplating a multi week deep water voyage,sailing the Caribbean, as well as armchair "deepwater sailors"/dreamers(like me?) The description of the passage between Durban and Cape Town is particularly interesting, informative and could be very useful to sailors .
The section on the Caribbean and the vagaries of Cruise Ships (I hesitate to call these floating hotels ,Liners) would help those sailing there (especially relevant with the news of the Shipwreck on the Italian isle this last week end)
Should be recommended reading for Naval and Coastguard personell
So you are basically against the whole idea of multihulls?
Dear Anonymous:
No, I am not basically against the whole idea of multihulls.
John V.
Post a Comment