Water
ballast, in one form or another, has been around for the past 150
years. It has only been in the last 20 years that racing boats have
utilized water ballast as a performance enhancing feature in their
design criteria. We have seen this development primarily in the Open
Class 30s, 40s, 50s, and 60s as well as the Whitbread 60s (Volvo
60s), and more recently, Class 40s. The use of water ballast has added
to the strategy and excitement of
these ocean racers and has become a proven, accepted feature as well as
being reliable and safe.
Why does water ballast work? Like crew on the rail, water ballast adds
weight outboard to increase a boat's stability, or righting moment,
helping it to sail more
upright. This is important because a sailboat's hull drag is usually
the
least when sailed upright. As the boat heels, hull drag increases and
the boat slows down. Also, lift on the appendages decreases with an
increase in heel angle, so the yacht's
pointing ability is reduced. It's a similar principle for the sails as
excessive heel will cause a reduction in lift and an increase in sail
drag.
So when the seas are running and the breeze is heavy, a water ballasted
yacht has a distinct advantage of being able to stabilize herself and
become a more powerful offshore design. Sailing close-hauled in breeze
is usually the time to carry the additional ballast as the boat will be
heeling the most. Off the wind, it's often more advantageous to sail
with the tanks empty or partially full depending upon the conditions. However, if the wind and sea are running fairly high,
then water ballast could be carried in both port and starboard tanks for proper
weight and trim distribution. The
extra weight of
the water will keep the boat steady in waves. If the boat hobby-horses (pitch moment)
too much, drag increases in both the rig and hull, and the boat's efficiency through the water decreases dramatically.
If
the water ballast tanks are
divided into multiple compartments fore
and aft, certain sections may be filled to correct for trim. These
compartments would then be sub-divided with baffles to combat any free
surface effects caused by the water sloshing back and forward.
Depending
upon the design, trial-and-error is necessary to optimize performance
and develop a strategy for the use of the system for any given weather
conditions. Even in light air conditions water ballast can be an
advantage.
By inducing heel the sails can hang full and continue to draw, keeping
the boat going. The increased momentum created by the added weight also
keeps the boat drifting forward when the puffs pass by.
When racing offshore or sailing shorthanded, classes like the Open 60s (left), Class 40s (above), and Mount Gay
30s have a
full range of stability available via their water ballast tanks.
This added righting moment gives the boat a marked
performance increase in a variety of sea and wind conditions. The Mount
Gay 30 Rule
allows up to 600 litters of water ballast total. That is 300 litters
each side, equivalent to 307.5 kgs per side. At 72.6 kgs per crew
member, that's equal to 4 1\4 crew members for on-the-wind conditions.
The stability characteristics of
a Mount Gay 30 are a product of the
Rules which define the boats dimensions: length, beam, draft,
displacement, keel weight, keel center of gravity, mast weight, and
mast center of gravity. The keel moment (keel weight times the distance
between its center of gravity and the flotation waterplane) must be at
least 1,180 kg-m which is easy to achieve for boats of normal
proportions. However, in the unlikely event that the keel moment is
less than this limit, then the boat must undergo a stability test. This
involves pulling the boat over to 90 degrees heel and weighting the
mast with 70 kgs (154.3 lbs) at the top of the jib halyard (IG
measurement). The boat must at least balance this way, or preferably
return upright, but not turn turtle. With such well-defined parameters, the 600 liter (158.5 gals) capacity of the water ballast
tanks
was determined as a safe and prudent amount.
The only design restrictions other than maximum capacity are that the
tanks, which must be located aft of the chainplates, be integral or
permanently secured to the hull, and be symmetrically arranged about
the boats center line. The tanks must be plumbed with one system of
pumps and valves. The pumps may be manual or powered. If power operated there must be a manual back-up. The inlets may
be flush openings or retractable inlet scoops to take advantage of the
ram effect at high speeds.
There
are definitely strategic advantages to racing with water ballast,
particularly on longer offshore competitions where there is little
tacking to do. Water
ballast can be taken on when you need it, you don't have to feed it, it
doesn't talk back to you,
and you can dump it when its usefulness has expired. The negative side
is that, the plumbing requires some occasional maintenance and you
don't have as many warm bodies who can handle lines. Conversely,
for round-the-cans racing where the ability to tack quickly is a
necessity, dealing with water ballast become impractical. Crew weight,
rather than transferring water, is far more efficient on these
short, inshore courses as there are people to handle lines and
reposition their
weight for the best boat trim.
The system on the VG30 is quite simple and can be readily applied to
boats of a similar size. Water is pumped on board with an electric pump
or the hand pump
backup. The 30 gpm electric pump may be brought on line at any time and
takes
approximately 2-1/2 minutes to fill a tank. The flow controls are
located in
the cockpit just forward of the traveler, providing quick and
convenient access to the trimmer. The plumbing of the tanks is designed
to be simple, easy to maintain,
yet highly efficient. There are only three flow controls to this
system; the 3" dia. inlet/outlet gate valve, and two port and starboard
gate valves for the 3" dia transfer pipe. Two-way diverter valves are
located down below to switch from the tank fill to a bilge pickup. The
gate valves are all spring-loaded with shock cord (positive closed) and
controlled lanyards leading up into
the cockpit which can be held open by cam-cleating the lanyard in
place.
Operating the water ballast system couldn't be easier. To pump water
into the port tank, the starboard and overboard gate valves are closed.
Begin pumping until the port breather valves, located on the shear,
blow water. To dump the water ballast, simply open the port and
overboard gate valves, and the water will drain out with gravity.
Tacking the VG30 with water ballast is just as easy. Prior
to the tack, open both port and starboard gate valves, keeping the
overboard gate valve closed, so the water will downflood from one side to the other. The transfer should take
approximately 30 to 40 seconds, and once it is complete, close both
gate valves and tack. It's almost like roll tacking the boat! If there
is any water loss, the new windward tank can be easily topped up with a
few strokes on the hand pump.
Water
ballast, in one form or another, has been around for the past 150
years. It has only been in the last 20 years that racing boats have
utilized water ballast as a performance enhancing feature in their
design criteria. We have seen this development primarily in the Open
Class 30s, 40s, 50s, and 60s as well as the Whitbread 60s (Volvo
60s), and more recently, Class 40s. The use of water ballast has added
to the strategy and excitement of
these ocean racers and has become a proven, accepted feature as well as
being reliable and safe. 
