Jack Line - A Jackline runs along the luff of the mainsail below the first reef. It passes through cringles in the sail and carries the luff slides. When the sail is at full hoist, the Jackline is tight and the sail is held against the mast. When you reef, the jack line goes slack allowing the reefed section of the luff to move away from the mast allowing the reef cringle to reach the gooseneck.
Jacobs Ladder - A rope ladder, lowered from the deck, as when pilots or passengers come aboard.
Jetty - A structure, usually masonry, projecting out from the shore; a jetty may protect a harbor entrance.
Jettison - To throw overboard.
Jib - A triangular foresail in front of the mast.
Jiffy Reefing - A fast method of reefing. Lines pull down the luff and the leech of the sail, reducing its area. This method is also known as slab reefing.
Jumper Stay - A short stay supporting the top forward portion of the mast. The stay runs from the top of the mast forward over a short jumper strut, then down to the mast, usually at the level of the spreaders.
Keel - In wooden boats, a strong structural member that runs from the bow to the stern and serves as a spine, providing the major source of the structural strength of the hull. Also, the projection below the hull that provides lateral resistance to leeway and carries the ballast that provides the boats righting moment or resistance to healing
Keelson - A structural member above and parallel to the keel.
Kick-up- Describes a rudder or centerboard that rotates back and up when an obstacle is encountered. Useful when a boat is to be beached.
Knockabout - A type of schooner without a bowsprit.
Knot - A measure of speed equal to one nautical mile per hour (1 knot = 1.15 miles / hr). A fastening made by interweaving rope to form a stopper, to enclose or bind and object, to form a loop or a noose, to tie a small rope to an object, or to tie the ends of two small ropes together.
Knotmeter - An instrument for measuring boat speed in nautical miles per hour. Typically measures speed through the water, as opposed to speed over ground. The speed of the current will affect the speed a knotmeter reads, hence the difference between speed through the water and speed over ground.
Latitude - The distance north or south of the equator measured and expressed in degrees, minutes, and seconds. Example: 38 deg, 15 min, 32 seconds North.
Lazarette - A storage space in a boat's stern area.
Lazy Jacks - Light lines run from the mast to the boom, in pairs, forming a cradle into which the mainsail may be lowered.
Lead - Refers to the direction in which a line goes. A boom vang, for example, may "lead to the cockpit."
Leech - The aft edge of a triangular sail. Frequently a light line, the Leech Line, runs through the leech of the sail and is used to tighten the leech against flogging.
Lee - The side sheltered from the wind.
Leeward - The direction away from the wind. Opposite of Windward.
Leeway - The sideways movement of the boat caused by either wind or current.
Lee Boards - Pivoting boards on either side of a boat which serve the same function as a centerboard. The board to leeward is dropped, the board to windward is kept up.
Lines - Rope or cordage used for various purposes aboard a boat.
Log - A record of courses or operation. Also, a device to measure speed.
Longitude - The distance in degrees east or west of the meridian at Greenwich England.
Loose-Footed - Describes a mainsail attached to the boom at the tack and clew, but not along the length of it's foot.
Lubber Line - A mark or permanent line on a compass indicating the direction forward parallel to the keel when properly installed.
Luff - The forward edge of a triangular sail. In a mainsail the luff is the edge along the mast.
Luff or Luffing - When a sailboat is brought too far into the wind or a sail is trimmed too far outboard and the forward edge or Luff of the sail begins to backwind or flutter.
Luff Tape - Installed on the luff of a roller furling headsail. The luff tape is fed into a groove on the foil of a roller furler to secure the sail to the furler.
Machine Pitch Prop - A prop with at least a 50% blade area of the described circle. This style prop yields more thrust for situations like clawing off of a lee shore, powering into wind or current, or maneuvering into and out of slips, but adds a little bit of drag when under sail compared to a “Sailor Prop”.
Mainmast - The tallest (or only) mast of the ship; on a schooner, the mast furthest aft.
Mainsail - The primary sail on the mainmast. On a sloop rig it is the large triangular sail bounded by the mast and boom. Lowest square sail on the mainmast.
Marline - A light twine size line which has been tarred.
Marline Spike - A tool for opening the strands of a rope while splicing.
Mast - Main vertical spar used to support sails and their running rigging and in turn is supported by standing rigging
Mast Step - Fitting or construction into which the base of the mast is placed.
Masthead Rig - A design in which the forestay runs to the top of the mast.
Mechanical advantage (or purchase) - A mechanical method of increasing an applied force. Disregarding the effects of friction, if a force of 100 pounds is applied to a 4 part tackle it is magnified to a force of 400 pounds. The purchase or mechanical advantage is said to be four to one, or 4:1.
Midship - Approximately in the location equally distant from the bow and stern.
Mizzen - A fore and aft sail flown on the mizzenmast.
Monkey Deck - A false deck built over a permanent deck. Often used in the bow of larger sailing ships, forward of the anchor windlass and provides a working platform around the portion of the bowsprit as it attaches to the ship.
Mooring - An arrangement for securing a boat to a mooring buoy or a pier.
MP3 Prop - A specific type of Machine Pitch Prop with skewed and raked asymmetrical blades and a blade area of 53%.
Nautical Mile - One minute of latitude; approximately 6076 feet - about 1/8 longer than the statute mile of 5280 feet.
Navigation - The art and science of conducting a boat safely from one point to another.
Navigation Regulations (or COLREGS) - The regulations governing the movement of vessels in relation to each other, generally called steering and sailing rules.
Oar - Device used to propel small boats by rowing.
Outboard - Toward or beyond the boat's sides. A detachable engine mounted on a boat's stern.
Outhaul - Usually a line or tackle, an outhaul is used to pull the clew of the mainsail towards the end of the boom, thus tightening the foot of the sail.
Overhaul - Straightening out misaligned or partially fouled sails and rigging. Also to overtake another vessel.
Overboard - Over the side or out of the boat.
Packing - Material that is installed in a stuffing box to provide a water tight seal. Most commonly refferring to a prop shaft.
Painter - A line used for docking on the bow, also known as the bow line.
Pay Out - To feed line over the side of the boat, hand over hand.
Pedestal - A vertical post in the cockpit used to elevate the steering wheel into a convenient position
Pier - A loading platform extending at an angle from the shore.
Pile - A wood, metal or concrete pole driven into the bottom. Craft may be made fast to a pile; it may be used to support a pier (see PILING) or a float.
Piling - Support, protection for wharves, piers etc.; Constructed of piles (see PILE)
Pilothouse - A small cabin on the deck of the ship that protects the steering wheel and the crewman steering.
Piloting - Navigation by use of visible references, the depth of the water, etc.
Pinch - To sail too close to the wind.
Pintle - The pin or bolt on which a ships rudder pivots. The pintle rests in the gudgeon.
Planing - A boat is said to be planing when it is essentially moving over the top of the water rather than through the water.
Planing Hull - A type of hull shaped to glide easily across the water at high speed.
Planking - Wood boards that cover the frames outside the hull.
Point - To effectively sail upwind. To sail close-hauled.
Port - A harbor or the left side of a boat looking forward. On February 18, 1846- Secretary of the Navy George Bancroft issues the General Order to change "Larboard" to "Port" for identification of the left side of a sailing vessel.
Priveledged Vessel - A vessel which, according to the applicable Navigation Rule, has right-of-way (this term has been superseded by the term "stand-on").
Pulpit - Provides a safety railing and serves as an attachment for the lifelines at the bow.
Pushpit - Provides a safety railing at the stern.
Quarterberth - A single bunk tucked under the cockpit, aligned fore and aft. Skippers often prefer this berth as it allows them to remain close to the cockpit while off watch. It also removes the need for a lee cloth to keep them in the berth during heavy seas, as the quarterberth is closed up every except at the head of the berth.
Quartering Sea - Sea coming on a boat's quarter.
Queen topsail - Small stay sail located between the foremast and mainmast.
Rake - The fore or aft angle of the mast. Can be deliberately induced (by adjustment of the standing rigging) to flatten sails, balance steering, etc. Normally slightly aft.
Reef Points - A pair of grommets installed at the fore and aft edges of the sail, intended to allow the running of lines to reduce sail area during heavy winds. Often includes lighter lines in between the grommets on the sail to tie off the sail to the boom to keep it tidy while reefed.
Rigging: - The lines that hold up the masts and move the sails (standing and running rigging).
Roach - It is common for sailmakers to add an arc of extra material on the leech, outside a line drawn from the head to the clew, this is known as the roach.
Rocker - The upward curvature of the keel towards the bow and stern.
Rode - The anchor line and/or chain.
Roller Reefing - Reduces the area of a sail by rolling it around a stay, the mast, or the boom. Most common on headsails.
Rope - In general, cordage as it is purchased at the store. When it comes aboard a vessel and is put to use it becomes line. Notable exceptions: A bell rope, a bolt rope.
Rubrail - Also rubbing strake or rub strake. An applied or thickened member at the rail, running the length of the boat; serves to protect the hull when alongside a pier or another boat.
Rudder - A vertical plate or board for steering a boat.
Run - To allow a line to feed freely through a block or fairlead, and is also when you are sailing with the wind behind you at your stern. In electrical language, a length of wire or an installation of wire.
Running Backstay - Also runner, or preventive backstay. A stay that supports the mast from aft, usually from the quarter rather than the stern. When the boat is sailing downwind, the runner on the leeward side of the mainsail must be released so as not to interfere with the sail.