Updates: March 2000
|Daily Updates: May 2000
with light rain
Latitude: 1 deg 45N
Longitude: 102 deg 17W
Wind Direction: NNW
Wind Speed: 16 Knots
Sea State: 1
Swell(s) Height: 3-5 Foot
Sea Temperature: 84.2°F (29°C)
Barometric Pressure: 1013 MB
Visibility: 5-10 Nautical Miles
Creamed tuna on toast
Hash browns and hot cereal
Bacon and sausage
Eggs to order
Mangos and melons
Grilled ham and cheese sandwich
Homemade Chocolate chip cookies
Fried Italian squash
Fresh baked dinner rolls
Chocolate cherry swirl cake
Homemade banana ice cream
here to see a biological community.
Maneuvering the RV Melville
April 14, 2000
By Capt. Eric Buck
Perhaps you’ve heard the phrase “where the rubber
meets the road”? Besides being a slang term relating to performance,
that’s where you get a lot of what is known as “traction”.
One definition of traction is “the adhesive friction of a body on
a surface on which it moves”. That’s why your car tires and
your shoe soles are made of rubber; so you get lots of traction and can
go where you want to go.
Driving a ship is not like driving a car! A ship is floating
in water and so it has a lot less traction than we enjoy on land. That means
much more time and distance are required to speed up, slow down, and even
turn the ship. This is complicated by the sheer size and bulk of the vehicles
involved. Your average family car probably weighs between 2,000 and 4,000
pounds, and it responds quickly because of the traction with a solid surface.
RV Melville is a relatively small ship (85 meters long), but even so, she
tips the scales at more than 2,700 long tons (that’s more than six
million pounds!) on the average trip . So in maneuvering the ship, there
is a lot of inertia and momentum to be dealt with. For example, a loaded
super tanker, which can weigh well over 250,000 long tons, may travel several
miles in the original direction of motion before stabilizing on a new course
Aboard ship, the Captain and the deck officers (often called
Mates) navigate and maneuver the ship to get to the desired destination.
Out on the open ocean, the deck officers themselves determine and execute
whatever maneuvers are necessary. When the ship is near shore or in hazardous
waters, such as channels and harbors, the maneuvering falls to the person
with the most experience; usually the Captain. The practice of maneuvering
a ship is called “shiphandling”.
The shiphandler must know all about the ship’s characteristics,
such as tonnage, propulsion system, rudders, response times, etc. Even the
underwater shape of the hull and the size of the superstructure (the part
of the ship above deck) may need to be factored into maneuvering decisions.
A shiphandler must always be thinking ahead about the time and distance
it will take before the ship responds to a change in direction or speed.
Unlike a car, there are no brakes that will stop you very quickly! When
a ship must come to a new speed or heading, the action to make it happen
must occur at some time or distance before it is actually needed. This time
or distance can be calculated -- and for precise maneuvers, it is. In most
cases, however, a shiphandler relies on experience and an intimate knowledge
of the vessel to execute maneuvers in time. No two ships are alike, and
even sister ships will handle differently. While a textbook knowledge of
the techniques and forces involved is important, a shiphandler gets good
at it only through actual hands-on experience. A seasoned shiphandler will
also employ a good measure of “seaman’s eye” in judging
speed, time, and distance.
Besides the ship-generated forces, such as from propellers
and rudders, there are other forces that the shiphandler must contend with.
Wind can push a ship in an unintended direction, and currents in the water
can do it even faster. In shallow waters and channels, or near structures
like piers and wharves, other forces with names like bow cushion, stern
suction, and squat come into play. Any one of these forces can lead to disaster
if they are not taken into account. By thinking ahead and planning, the
shiphandler can actually use these adverse adverse forces to help, rather
than hinder, the maneuver.
Many ships use a fixed propeller on a horizontal shaft to
push themselves through the water. A rudder is mounted behind the
propeller to steer the ship. RV Melville is among a growing group
of vessels using “azimuthing
(directional) propellers” or “thrusters” to drive themselves.
These vessels have no rudders. The propellers can be swiveled on
a vertical shaft to get thrust in any direction. RV Melville has
two such thrusters mounted side by side at the stern of the ship, one port
and one starboard. The propellers are about nine feet in diameter and are
mounted inside a nozzle (see today’s slide show). RV Melville carries
a third thruster in the bow of the ship. This bow thruster, or B/T for short,
is used in conjunction with the stern thrusters to give the ship a very
high degree of precise maneuverability. It is used when holding a position
out at sea or when maneuvering alongside a dock in a harbor. When not in
use, it is retracted into the hull.
Each thruster has its own controller on the Bridge so the
shiphandler can manually set azimuth (direction) and RPM (revolutions per
minute of the propeller). RV Melville also has a dynamic positioning system
(DPS). When we are using the DPS, the control of all three thrusters, or
any combination of them, is turned over to a single joystick. The combination
of thrusters and joystick control allows the shiphandler to do some pretty
fancy maneuvers, including turning the ship on a dime and moving sideways
through the water! The ship responds to the thrusters very quickly, which
greatly reduces the lead in time and distance that we talked of earlier.
For certain scientific operations, it is important to hold the ship in position
for hours, sometimes days. The DPS can hold the ship within a 10-meter radius,
even in 40 knots of wind, 20-30 foot waves, and several knots of surface
Shiphandling is a very technical subject and I’ve just given you
the basics here. There are lots of excellent books out there. One of my
favorites is Crenshaw’s Naval Shiphandling published by the Naval
Institute Press. Another noteworthy publisher of technical nautical
books is Cornell Maritime Press.