Maritime Mobile Service Network

Official information issued by tropical cyclone warning centers describing all tropical cyclone watches and warnings in effect along with details concerning tropical cyclone locations, intensity and movement, and precautions that should be taken. Advisories are also issued to describe: (a) tropical cyclones prior to issuance of watches and warnings and (b) subtropical cyclones.

Aft:

Toward the rear of the vessel.

Apparent Wind:

The perceived wind direction of a moving yacht. When the yacht goes faster, the perceived wind direction moves forward, just as the wind always seems to hit a car only from head-on as it drives at high speeds.

Backstay:

A mast support that runs from the top of the mast to the stern of the yacht; it may be adjustable in order to bend the mast backward or to increase tension on the forestay.

Ballast:

Weight in the keel of a boat to add stability (righting moment).

Beam:

A boat's greatest width.

Beating:

Sailing (or pointing) at an angle into the wind or upwind. Since sailboats cannot sail directly into the wind, "beating" is the closet course to the wind they can sail.

Berth:

place where you but the boat on a dock.
bunk or sleeping quarters.

Bilge:

The lowest part of a boat's hull.

Block:

A deck or track-mounted pulley device through which ropes such as jib and genoa sheets are strung.

Boom:

A spar to which a sail's lower edge or "foot" is attached. The boom is attached to the mast at the gooseneck.

Bosun's Chair:

A seat, usually made of canvas, used to hoist a person up the mast.

Bow:

The front of the boat.

Bowman:

The crewmember in charge of sail changes and keeping a lookout on the bow at the start.

Broach:

When a keelboat sailing on a run capsizes from a strong puff of wind or gets knocked down by a wave. Also called a Knockdown or a Wipeout.

Bulb:

The lead-torpedo shape on the bottom of the keel.

Bulkhead:

A partition to strengthen the frame of a yacht.

Bouy:

A marker used for navigation, mooring, or racing around.

Cam Cleat:

A mechanical cleat used to hold a line automatically. It uses two spring-loaded cams (teeth) that come together to clamp the line, which is placed between them.

Capsize:

To turn upside down.

Central North Pacific Basin:

The region north of the Equator between 140W and the International Dateline. The Central Pacific Hurricane Center (CPHC) in Honolulu, Hawaii is responsible for tracking tropical cyclones in this region.

Chainplates:

The metal or composite attachments for shrouds and stays. Part of the hull, connecting the hull with the rig.

Chute:

A spinnaker.

Cleat:

A fitting, typically with projecting ends, that holds a line against the tension from the sails, rigging or mooring.

Clew:

The lower corner of a mainsail, jib or genoa and either lower corner of a spinnaker attached to the sheet.

Cockpit:

A recessed area in the deck in which the crew works.

Code Ø:

A tight luff, upwind spinnaker developed by EF Language during the 1997-98 Whitbread race, also called "the Whomper".

Compass:

An instrument that uses the earth's magnetic field to point to the direction of the magnetic North Pole; used by navigators to determine the direction a yacht is heading and to set a course.

Course:

The direction a yacht is sailing.

Crew:

The team of sailors that sails the yacht.

Cyclone:

An atmospheric closed circulation rotating counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Dacron:

A white woven sailcloth made of polyester fiber. Brand name by DuPont.

Dead Downwind:

Sailing straight with the wind.

Deck:

Horizontal surface or platform of a yacht.

Delaminating:

A failure of the bond between either of the hull's outer and inner skins, and the "sandwich" spacing material in between-allowing either of the two outer layers to become unstuck from the core.

Dismast:

To lose, through breakage, part or all of the mast.

Doldrums:

An area between the weather systems of the Northern and Southern Hemispheres characterized by frustrating light winds, major shifts in wind direction and sudden violent squalls.

Downwind:

The point of sail when the wind blows from aft of the yacht's beam.

Eastern North Pacific Basin:

The portion of the North Pacific Ocean east of 140W. The National Hurricane Center in Miami, Florida is responsible for tracking tropical cyclones in this region.

EPIRB:

Emergency Position Indicating Radio Beacon. There are two types of beacon. One is a transmitter that all commercial vessels are required to have on board. Pleasure crafts are recommended to carry one. The second type is a personal EPIRB that sailors wear on themselves, either as a watch, within their clothing, or around their neck so they can be located should they be washed overboard.

Equator:

Line of latitude at 0 degrees -- equal distance from both poles.

Eye:

The roughly circular area of comparatively light winds that encompasses the center of a severe tropical cyclone. The eye is either completely or partially surrounded by the eyewall cloud.

Eyewall / Wall Cloud:

An organized band or ring of cumulonimbus clouds that surround the eye, or light-wind center of a tropical cyclone. Eyewall and wall cloud are used synonymously.

Extratropical:

A term used in advisories and tropical summaries to indicate that a cyclone has lost its "tropical" characteristics. The term implies both poleward displacement of the cyclone and the conversion of the cyclone's primary energy source from the release of latent heat of condensation to baroclinic (the temperature contrast between warm and cold air masses) processes. It is important to note that cyclones can become extratropical and still retain winds of hurricane or tropical storm force.

Extratropical Cyclone:

A cyclone of any intensity for which the primary energy source is baroclinic, that is, results from the temperature contrast between warm and cold air masses.

Flash Flood Warning:

A weather warning issued when a flash flood is imminent and immediate action is necessary.

Flash Flood Watch:

A weather watch issued when there is a potential for flash flooding in a given area.

Foot:

The bottom edge of a sail.

Foredeck:

The area of a yacht's deck that is in front of the mast; also a crew position aboard a racing yacht.

Foresail:

Any sail used between the mast and the forestay.

Forestay:

A mast support that runs from the top of the mast, or near the top of the mast, to the bow.

Fractional Rig:

A rig where the headstay does not go to the bottom of the mast.

Furious Fifties:

An area between 50 degrees and 60 degrees latitude noted for very strong winds and huge seas.

Fujiwhara Effect:

The tendency of two nearby tropical cyclones to rotate cyclonically about each other.

Gale Warning:

A warning of 1-minute sustained surface winds in the range 34 kt (39 mph or 63 km/hr) to 47 kt (54 mph or 87 km/hr) inclusive, either predicted or occurring and not directly associated with tropical cyclones.

Galley:

Kitchen.

Gennaker:

A cross between a genoa and a spinnaker, a foresail used for reaching.

Genoa:

A large foresail that overlaps the shroud base used for sailing upwind; also called a "genny".

GPS:

Global Position System. Satellite navigation, which gives yachts exact latitude and longitude position. The update race is one second.

Guy:

A rope used to adjust the position of a spinnaker pole.

Gybe:

See Jibe.

Gooseneck:

The mechanical device connecting the boom and the mast.

Halyard:

A line used to hoist and hold up a sail.

Head:

Toilet/Basin/Shower.
The top corner of a sail that is connected to the halyard.

Header:

A wind shift during which the wind enters the boat more forward.

Headsail:

A sail flown between the mast and the bow of the yacht.

Helm:

The steering station of a yacht; the tiller or wheel by which the rudder is controlled.

Helmsman:

The crewmember who steers the yacht; usually also the skipper; also called the "driver".

High Wind Warning:

A high wind warning is defined as 1-minute average surface winds of 35 kt (40 mph or 64 km/hr) or greater lasting for 1 hour or longer, or winds gusting to 50 kt (58 mph or 93 km/hr) or greater regardless of duration that are either expected or observed over land.

Hounds:

The attachment points for the shrouds up the mast.

Hull:

The body of a yacht.

Hurricane / Typhoon:

A tropical cyclone in which the maximum sustained surface wind (using the U.S. 1-minute average) is 64 kt (74 mph or 119 km/hr) or more. The term hurricane is used for Northern Hemisphere tropical cyclones east of the International Dateline to the Greenwich Meridian. The term typhoon is used for Pacific tropical cyclones north of the Equator west of the International Dateline.

Hurricane Local Statement:

A public release prepared by local National Weather Service offices in or near a threatened area giving specific details for its county/parish warning area on (1) weather conditions, (2) evacuation decisions made by local officials, and (3) other precautions necessary to protect life and property.

Hurricane Season:

The portion of the year having a relatively high incidence of hurricanes. The hurricane season in the Atlantic, Caribbean, and Gulf of Mexico runs from June 1 to November 30. The hurricane season in the Eastern Pacific basin runs from May 15 to November 30. The hurricane season in the Central Pacific basin runs from June 1 to November 30.

Hurricane Warning:

An announcement that hurricane conditions (sustained winds of 74 mph or higher) are expected somewhere within the specified area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds.

Hurricane Watch:

An announcement that hurricane conditions (sustained winds of 74 mph or higher) are possible within the specified area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch is issued 48 hours in advance of the anticipated onset of tropical-storm-force winds.

Indirect Hit:

Generally refers to locations that do not experience a direct hit from a tropical cyclone, but do experience hurricane force winds (either sustained or gusts) or tides of at least 4 feet above normal.

Inmarsat-C:

A digital store and forward messaging service, using satellites for transmission.

Invest:

A weather system for which a tropical cyclone forecast center (NHC, CPHC, or JTWC) is interested in collecting specialized data sets (e.g., microwave imagery) and/or running model guidance. Once a system has been designated as an invest, data collection and processing is initiated on a number of government and academic web sites, including the Naval Research Laboratory (NRL) and the University of Wisconsin Cooperative Institute for Meteorological Satellite Studies (UW-CIMSS). The designation of a system as an invest does not correspond to any particular likelihood of development of the system into a tropical cyclone; operational products such as the Tropical Weather Outlook or the JTWC/TCFA should be consulted for this purpose.

Jib:

A foresail that fits in between the forestay and the mast.

Jibe:

The process of turning the yacht so the stern turns through the wind, thereby changing the side of the yacht on which the sails are carried (opposite of tacking); also spelled gybe.

Jury-rig:

Emergency rigging with available gear, usually due to a broken mast.

Keel:

A ballasted appendage projecting below the boat that keeps it from capsizing, which also supplies the hydrodynamic lateral force that enables the boat to sail upwind.

Kevlar:

Man-made, yellow/brown aramid fiber that is used to make sails or composites for building hulls. In sails it retains its shape better and is lighter than Dacron, but is more expensive. Kevlar is the brand name from DuPont and is also used in bullet-proof jackets. It loses its good properties when exposed to the sun for extended periods of time.

Kite:

A spinnaker.

Knockdown:

See Broach.

Knot:

One nautical mile per hour.
Connection of lines.

Landfall:

The intersection of the surface center of a tropical cyclone with a coastline. Because the strongest winds in a tropical cyclone are not located precisely at the center, it is possible for a cyclone's strongest winds to be experienced over land even if landfall does not occur. Similarly, it is possible for a tropical cyclone to make landfall and have its strongest winds remain over the water. Compare direct hit, indirect hit, and strike.

Latitude:

Angular distance north or south of the equator, measured from 0 to 90 degrees north or south.

Layline:

An imaginary line projecting at an angle corresponding to the wind direction from either side of a racecourse marker buoy that defines the optimum sailing angle for a yacht to fetch the mark or the finish line. When a yacht reaches this point, it is said to be "on the layline". Going beyond the layline means the yacht is sailing a greater distance to reach the mark or finish line.

Leech:

The trailing edge of a sail.

Leeward:

Away from the wind. A leeward yacht is one that has another yacht between it and the wind (opposite of windward).

Life Raft:

An inflatable craft into which the crew of a yacht transfers if the yacht intends to sink.

Lifelines:

Cables that are held in place by stanchions and go around the boat to prevent people from falling overboard. A "fence" around the boat on the edge of the deck.

Lift:

A wind shift during which the wind enters the boat from further back. It allows the helmsman to head up or alter course to windward, or the crew to ease the sheets.

Lines:

A nautical term for ropes.

Longitude:

Angular distance east or west of the Greenwich Meridian, measured from 0 t 180 degrees east or west.

Luff:

To change course toward the wind.
The leading edge of a sail.

Mainsheet Trimmer:

A device that controls the position and shape of the mainsail, the large triangular sail behind the mast.

Major Hurricane:

A hurricane that is classified as Category 3 or higher.

Mast:

The vertical spar that holds up the sails.

Mastman:

The crewmember who works the lines on the mast when hoisting sails, and who assists the bowman with the work on the foredeck.

Masthead Rig:

A rigging scheme in which the forestay is attached near the top of the mast. See Fractional Rig.

Match Racing:

A racing format where only two yachts compete at a time, like a boxing match, as opposed to "fleet racing" where more yachts sail at once.

Maxi:

A boat designed to the maximum rating allowed under the International Offshore Rule, or more recently, the international measurement system.

Models:

Numerical computer models which attempt to forecast the state of the atmosphere and future storm intensity/movement.

National Geodetic Vertical Datum of 1929 [NGVD 1929]:

A fixed reference adopted as a standard geodetic datum for elevations determined by leveling. The datum was derived for surveys from a general adjustment of the first-order leveling nets of both the United States and Canada. In the adjustment, mean sea level was held fixed as observed at 21 tide stations in the United States and 5 in Canada. The year indicates the time of the general adjustment. A synonym for Sea-level Datum of 1929. The geodetic datum is fixed and does not take into account the changing stands of sea level. Because there are many variables affecting sea level, and because the geodetic datum represents a best fit over a broad area, the relationship between the geodetic datum and local mean sea level is not consistent from one location to another in either time or space. For this reason, the National Geodetic Vertical Datum should not be confused with mean sea level.

Nautical Mile:

The unit of geographical distance used on "salt-water" charts. 1 nautical mile corresponds exactly to 1 minute of angular distance on the meridian (adjacent left and right side of a sea chart). This facilitates navigation as it avoids a complicated conversion from angle to distance. 1 nautical mile equals 1.852 kilometers. 60 minutes equal 1 degree.

Navigator:

The crewmember who monitors the yacht's location and progress relative to the racecourse and the other yachts.

Off the Wind:

Sailing away from the wind, also downwind, reaching or running.

Peeling:

Changing from one spinnaker to another.

Pitch-poling:

Putting the bow into a wave and cart-wheeling forward.

Pitman:

Crewmember who controls the halyards and mast winches and assists the mastman.

Pole:

The spinnaker pole.

Port:

Nautical term for the left side of a yacht when facing forward.

Port Tack:

Sailing with the wind blowing onto the port side and the mainsail on the starboard side.

Post-storm Report:

A report issued by a local National Weather Service office summarizing the impact of a tropical cyclone on its forecast area. These reports include information on observed winds, pressures, storm surges, rainfall, tornadoes, damage and casualties.

Post-tropical Cyclone:

A former tropical cyclone. This generic term describes a cyclone that no longer possesses sufficient tropical characteristics to be considered a tropical cyclone. Post-tropical cyclones can continue carrying heavy rains and high winds. Note that former tropical cyclones that have become fully extratropical...as well as remnant lows...are two classes of post-tropical cyclones.

Preliminary Report:

Now known as the "Tropical Cyclone Report". A report summarizing the life history and effects of an Atlantic or eastern Pacific tropical cyclone. It contains a summary of the cyclone life cycle and pertinent meteorological data, including the post-analysis best track (six-hourly positions and intensities) and other meteorological statistics. It also contains a description of damage and casualties the system produced, as well as information on forecasts and warnings associated with the cyclone. NHC writes a report on every tropical cyclone in its area of responsibility.

Present Movement:

The best estimate of the movement of the center of a tropical cyclone at a given time and given position. This estimate does not reflect the short-period, small scale oscillations of the cyclone center.

Radius of Maximum Winds:

The distance from the center of a tropical cyclone to the location of the cyclone's maximum winds. In well-developed hurricanes, the radius of maximum winds is generally found at the inner edge of the eyewall.

Rapid Intensification:

An increase in the maximum sustained winds of a tropical cyclone of at least 30 kt in a 24-h period.

Reaching:

All angles against the wind that are not beating or dead downwind. A close reach has the wind forward of abeam; a beam reach is when the wind is perpendicular to the boat; and a broach reach is when the wind is aft of abeam.

Relocated:

A term used in an advisory to indicate that a vector drawn from the preceding advisory position to the latest known position is not necessarily a reasonable representation of the cyclone's movement.

Remnant Low:

A post-tropical cyclone that no longer possesses the convective organization required of a tropical cyclone...and has maximum sustained winds of less than 34 knots. The term is most commonly applied to the nearly deep-convection-free swirls of stratocumulus in the eastern North Pacific.

Rig:

The general term used to describe a yacht's mast and sail combination.

Rigging:

The wires, lines, halyards, and other items used to attach the sails and the spars to the boat. The lines that do not have to be adjusted often are known as standing rigging. The lines that are adjusted to raise, lower, and trim the sails are known as running rigging.

Roaring Forties:

The area between 40 degrees and 50 degrees latitude noted for strong winds and large seas.

Running:

Dead downwind.

Saffir-Simpson Hurricane Wind Scale:

The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 categorization based on the hurricane's intensity at the indicated time. The scale provides examples of the type of damage and impacts in the United States associated with winds of the indicated intensity. The following table shows the scale broken down by winds:

Category	Wind Speed (mph)	Damage
1	74 - 95	Very dangerous winds will produce some damage
2	96 - 110	Extremely dangerous winds will cause extensive damage
3	111 - 129	Devastating damage will occur
4	130 - 156	Catastrophic damage will occur
5	> 156	Catastrophic damage will occur

For a detailed description of the Saffir-Simpson Hurricane Wind Scale, click here.

Sat-phone:

A satellite telephone. Unlike cellular phones that relay on networks of local antennae, sat-phones send and receive their signals directly to and from orbiting satellites. Though significantly more expensive than cellular phones, with calls costing from $4 to $9 a minute, sat-phones can operate from almost anywhere on earth.

Screaming Sixties:

The area between 60 degrees and 70 degrees latitude noted for exceptionally strong wind, huge seas, and frequent icebergs.

Sheet:

A line that controls sails and adjusts their angle of attack and their trailing edge.

Shroud:

A cable or rod that supports the mast sidewise. Shrouds run from the chainplates at deck level on the port and starboard side, to the hounds just below the top of the mast.

Sked:

A position report issue every 6 hours.

Skipper:

The person in charge of a vessel.

Southern Ocean:

The ocean surrounding the Antarctic continent. The largest uninterrupted water on the earth with the most dynamic weather systems, the highest waves, and the strongest winds (apart from tropical storms).

Spinnaker:

A large ballooning sail that is flown in front of the yacht when the wind comes from aft of abeam. Spinnakers are used when running or reaching, sailing downwind. Also called Kite or Chute. The head is pulled to the top of the mast, using the halyard; the tack is at the spinnaker pole, projecting it away from the yacht; and the clew is connected to the sheet, trimming the sail.

Spinnaker Pole:

A pole that is attached to the lower front of the mast to hold one corner of a spinnaker out from the yacht. On high-performance yachts, spinnaker poles are usually made of strong but lightweight carbon fiber composite material. When a spinnaker is not being flown, the pole is tethered to the deck.

Squall:

The sudden, short-term burst of wind with passing clouds. May be accompanied by rain.

Stanchions:

Vertical poles that stand on the outer edge of the deck to hold the lifelines.

Standing Rigging:

The non-moving rods and lines that support the mast and sails.

Starboard:

Nautical term for the right half of the yacht when facing forward.

Starboard Tack:

Sailing with the wind blowing onto the starboard side, and the mainsail on the port side.

Stay:

A rod or wire that supports the mast in a fore/aft position.

Staysail:

A small sail flown between the mast and the inner forestay.

Stern:

The rear of the boat.

Storm Surge:

An abnormal rise in sea level accompanying a hurricane or other intense storm, and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal or astronomic high tide from the observed storm tide.

Storm Tide:

The actual level of sea water resulting from the astronomic tide combined with the storm surge.

Storm Warning:

A warning of 1-minute sustained surface winds of 48 kt (55 mph or 88 km/hr) or greater, either predicted or occurring, not directly associated with tropical cyclones.

Subtropical Cyclone:

A non-frontal low pressure system that has characteristics of both tropical and extratropical cyclones. This system is typically an upper-level cold low with circulation extending to the surface layer and maximum sustained winds generally occurring at a radius of about 100 miles or more from the center. In comparison to tropical cyclones, such systems have a relatively broad zone of maximum winds that is located farther from the center, and typically have a less symmetric wind field and distribution of convection.

Subtropical Depression:

A subtropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 33 kt (38 mph or 62 km/hr) or less.

Subtropical Storm:

A subtropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 34 kt (39 mph or 63 km/hr) or more.

Tack:

The process of turning the bow of the yacht through the wind and changing the sides of the sails.
The lower corner of a sail that is attached to the yacht.

Tiller:

Traditionally the piece of wood the helmsman holds to control the rudder. Now it can be made of aluminum, titanium or a composite material in order to save weight.

Top:

The high end of the mast.

Trade Wind:

Northeast and southeast winds in the Atlantic blowing continually toward the equator. Named after the traditional trading ships, which sailed a course using these winds to their advantage.

Transom:

The flat rear end of a boat, the upper part of which tends to lean forward on modern racers.

Trim:

To adjust the sail to make it the right shape and angle to the wind.

Tropical Cyclone:

A warm-core non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters, with organized deep convection and a closed surface wind circulation about a well-defined center. Once formed, a tropical cyclone is maintained by the extraction of heat energy from the ocean at high temperature and heat export at the low temperatures of the upper troposphere. In this they differ from extratropical cyclones, which derive their energy from horizontal temperature contrasts in the atmosphere (baroclinic effects).

Tropical Depression:

A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 33 kt (38 mph or 62 km/hr) or less.

Tropical Disturbance:

A discrete tropical weather system of apparently organized convection -- generally 100 to 300 nmi in diameter -- originating in the tropics or subtropics, having a nonfrontal migratory character, and maintaining its identity for 24 hours or more. It may or may not be associated with a detectable perturbation of the wind field.

Tropical Storm:

A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) ranges from 34 kt (39 mph or 63 km/hr) to 63 kt (73 mph or 118 km/hr).

Tropical Storm Warning:

An announcement that tropical storm conditions (sustained winds of 39 to 73 mph) are expected somewhere within the specified area within 36 hours.

Tropical Storm Watch:

An announcement that tropical storm conditions (sustained winds of 39 to 73 mph) are possible within the specified area within 48 hours.

Tropical Wave:

A trough or cyclonic curvature maximum in the trade-wind easterlies. The wave may reach maximum amplitude in the lower middle troposphere.

Trysail:

A triangular loose-footed sail fitted aft of the mast, often used to replace the mainsail in heavy weather.

Upwind:

Sailing against the wind at an angle a certain yacht can achieve.

Velocity Made Good (VMG):

The speed of a yacht relative to the waypoint it wants to reach, or toward or away from the wind.

Watches:

Teams within which the crew operates, taking turns to work, sleep and eat.

Watch Leader/Captain:

The person in charge of a watch.

Watertight Hatch:

Watertight doors. In the event of a hull breach, the hatches can be closed to seal off compartments on the affected portion of the boat.

Waypoint:

A specific location as defined by GPS, the Global Positioning System.

Winch:

A device used to give a mechanical advantage when hauling on the lines.

Winch Pedestal:

An upright winch drive mechanism with two handles to increase purchasing power.

Windward:

Against the wind.

Wipeout:

See Broach.