By Don Jordan,
inventor, retired aeronautical engineer
The series
drogue was developed to perform two separate functions:
1. To prevent
the capsize of monohull and multihull sailboats in the event of
a large breaking wave strike.
2. To improve
the motion of the boat in storm waves and to reduce drift.
Most storms
do not generate dangerous breaking waves. A vessel may go through
a lifetime of cruising without being struck by a breaking wave
even though hurricane winds have been encountered.
Although storm
waves move at speeds up to 30 knots, the water in the wave moves
at a much lower speed. A boat lying ahull is not subjected to
high forces. Experience and testing have shown that a well found
monohull with positive stability at 90 degrees roll angle has
little risk of being damaged by non-breaking storm waves. A multihull,
however may be capsized.
A dangerous
breaking wave is formed by the interaction of two or more storm
waves. This type of wave has a large mass of water at its crest
moving at wave speed (20-30 knots). When a vessel lying ahull
is struck by this moving mass of water, a very large force is
developed. In a typical event the boat has been successfully riding
out the storm for many hours, then, 10 seconds later it lies dismasted
and damaged. It is the function of the drogue to turn the stern
into this moving mass of water and pull it safely through.
The risk of
breaking wave capsize is dependent on the weight of the vessel,
with small light boats being at high risk. Above a length of 40'
the risk is diminished, and above 60' few, if any breaking wave
capsizes are on record.
On a conventional
monohull sailing yacht the underwater lateral surface is located
aft of the center of the boat while the topside area is greater
towards the bow. When struck by a moving mass of water the bow
of such a vessel is driven down by a powerful turning moment.
Therefore it is necessary to use a drogue from the stern rather
than a sea anchor from the bow to align the boat with the moving
water and pull the boat through.
A multihull
is relatively symmetrical fore and aft, although there is still
some tendency for the bow to be driven down by the wave. Testing
indicates that either a drogue or sea anchor, if properly designed,
can be effective in preventing breaking wave capsize. However,
the force required of the drogue is less than that required of
a sea anchor.
Some sailors
have expressed reluctance to use a drogue for fear of being "pooped".
Testing has shown that a conventional monohull or multihull will
perform in a safe manner when riding stern to the sea. Actually,
the stern generally has more local buoyancy than the bow and will
rise quickly to a steep sea. However, storm waves will have whitecaps
containing some moving water and this may splash aboard.
In a dangerous
breaking wave strike, moving water may sweep the cockpit and strike
the companionway doors. This is unavoidable, and is a necessary
corollary to saving the vessel.
RECOVERY:
The crew of a 40' ketch practiced several methods of taking in
the drogue in a Force 7 wind in the English Channel. They concluded
that the best system was to grind it in with a cockpit winch a
little at a time, letting the sea help you and belaying when the
pull was high. With a little care they avoided tearing any cones.
Another system is to prepare two helper lines, clap one line on
the drogue and winch in 3 or 4 feet, then repeat with the other
line. This takes 20 minutes or so, but is safe and not particularly
difficult.
Adding a light
line in parallel with the drogue to permit the drogue to be pulled
in backwards is definitely not recommended since it complicates
the gear and may lead to fouling under critical conditions.
NOTE:
If there are any questions Ace
Sailmakers is unable to answer, Don Jordan is willing to help:
Donald
Jordan
113 Evergreen Lane
Glastonbury, CT 06033
DonaldJordan@att.net
Phone: 1-860-633-1702
