Waterline length

Last updated
LOA (length overall) & LWL (length at the waterline) LOA-LWL.svg
LOA (length overall) & LWL (length at the waterline)
Detailed hull dimensions Ship length measurements.svg
Detailed hull dimensions

A vessel's length at the waterline (abbreviated to L.W.L) [1] is the length of a ship or boat at the level where it sits in the water (the waterline ). The LWL will be shorter than the length of the boat overall ( length overall or LOA) as most boats have bows and stern protrusions that make the LOA greater than the LWL. As a ship becomes more loaded, it will sit lower in the water and its ambient waterline length may change; but the registered L.W.L it is measured from a default load condition.

Contents

This measure is significant in determining several of a vessel's properties, such as how much water it displaces, where the bow and stern waves occur, hull speed, amount of bottom-paint needed, etc. Traditionally, a stripe called the "boot top" is painted around the hull just above the waterline.

In sailing boats, longer waterline length will usually enable a greater maximum speed, because it allows greater sail area,[ citation needed ] without increasing beam or draft. Greater beam and draft produces a larger wetted surface, thereby causing higher hull drag. In particular, any "displacement" or non-planing boat requires much greater power to accelerate beyond its hull speed, which is determined by the length of the waterline, and can be calculated using the formula: Vmax (in knots) = square root of LWL (in feet) x 1.34. The hull speed is the speed at which the wavelength of the bow wave stretches out to the length of the waterline, thus dropping the boat into a hollow between the two waves. While small boats like canoes can overcome this effect fairly easily, heavier sailboats cannot.

Since waterline length provides a practical limit for the speed of a typical sailboat, traditional rules for racing sailboats often classed boats using waterline length as a principal measure. To get around this rule, designers in the early 20th century began building racing sailboats with long overhangs fore and aft. This resulted in a nominally shorter waterline, but when the boats were sailed they heeled over, pulling the sides of the overhangs into the water as well and creating a much longer effective waterline, and thereby achieving much greater speed. The first recorded use of a line (documented by New Jersey marine museum) is by the small and rather unknown naval fleet of Thomas Jefferson.

See also

Notes

  1. Note: originally Load Waterline Length

Related Research Articles

Hull (watercraft) Watertight buoyant body of a ship or boat

A hull is the watertight body of a ship, boat, or flying boat. The hull may open at the top, or it may be fully or partially covered with a deck. Atop the deck may be a deckhouse and other superstructures, such as a funnel, derrick, or mast. The line where the hull meets the water surface is called the waterline.

Multihull Ship or boat with more than one hull

A multihull is a ship or boat with more than one hull, whereas a vessel with a single hull is a monohull.

Ship Large watercraft

A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguished from boats, based on size, shape, load capacity, and purpose. Ships have supported exploration, trade, warfare, migration, colonization, imperialism, and science. After the 15th century, new crops that had come from and to the Americas via the European seafarers significantly contributed to world population growth. Ship transport is responsible for the largest portion of world commerce.

Yacht Recreational boat or ship

A yacht is a sailing or power vessel used for pleasure, cruising, or racing. There is no standard definition, so the term applies to such vessels that have a cabin with amenities that accommodate overnight use. To be termed a yacht, as opposed to a boat, such a pleasure vessel is likely to be at least 33 feet (10 m) in length and may have been judged to have good aesthetic qualities.

Deck (ship) Part of a ship or boat

A deck is a permanent covering over a compartment or a hull of a ship. On a boat or ship, the primary or upper deck is the horizontal structure that forms the "roof" of the hull, strengthening it and serving as the primary working surface. Vessels often have more than one level both within the hull and in the superstructure above the primary deck, similar to the floors of a multi-storey building, that are also referred to as decks, as are certain compartments and decks built over specific areas of the superstructure. Decks for some purposes have specific names.

Sea anchor Drag device used to stabilize a boat in heavy weather and reduce drift

A sea anchor is a device that is streamed from a boat in heavy weather. Its purpose is to stabilize the vessel and to limit progress through the water. Rather than tethering the boat to the seabed with a conventional anchor, a sea anchor provides hydrodynamic drag, thereby acting as a brake. Normally attached to a vessel's bows, a sea anchor can prevent the vessel from turning broadside to the waves and being overwhelmed by them.

Hull speed or displacement speed is the speed at which the wavelength of a vessel's bow wave is equal to the waterline length of the vessel. As boat speed increases from rest, the wavelength of the bow wave increases, and usually its crest-to-trough dimension (height) increases as well. When hull speed is exceeded, a vessel in displacement mode will appear to be climbing up the back of its bow wave.

Rowing Act of propelling a boat using the motion of oars in the water

Rowing is the act of propelling a boat using the motion of oars in the water by displacing water to propel the boat forward. Rowing and paddling are similar. However, rowing requires oars to have a mechanical connection with the boat, while paddles are hand-held and have no mechanical connection.

Beam (nautical) Width of a ship at its widest point

The beam of a ship is its width at its widest point. The maximum beam (BMAX) is the distance between planes passing through the outer extremities of the ship, beam of the hull (BH) only includes permanently fixed parts of the hull, and beam at waterline (BWL) is the maximum width where the hull intersects the surface of the water.

The Pearson Triton, sometimes referred to as a Triton 28, is an American sailboat that was designed by Carl Alberg as a racer-cruiser and first built in 1958. It was introduced at the 1959 National Boat Show in New York City and was one of the first fiberglass boat designs built. The design also launched Alberg's career as a naval architect.

Length overall Maximum length of a vessels hull measured parallel to the waterline

Length overall is the maximum length of a vessel's hull measured parallel to the waterline. This length is important while docking the ship. It is the most commonly used way of expressing the size of a ship, and is also used for calculating the cost of a marina berth.

Length between perpendiculars Form of ship length measurement

Length between perpendiculars is the length of a ship along the summer load line from the forward surface of the stem, or main bow perpendicular member, to the after surface of the sternpost, or main stern perpendicular member. When there is no sternpost, the centerline axis of the rudder stock is used as the aft end of the length between perpendiculars.

Wave-making resistance Energy of moving water away from a hull

Wave-making resistance is a form of drag that affects surface watercraft, such as boats and ships, and reflects the energy required to push the water out of the way of the hull. This energy goes into creating the wave.

Draft (hull) Vertical distance between the waterline and the bottom of the hull (keel)

The draft or draught of a ship's hull is the vertical distance between the waterline and the bottom of the hull (keel). The draught of the vessel is the maximum depth of any part of the vessel, including appendages such as rudders, propellers and drop keels if deployed. Draft determines the minimum depth of water a ship or boat can safely navigate. The related term air draft is the maximum height of any part of the vessel above the water.

Sailing yacht Private sailing vessel with overnight accommodations

A sailing yacht, is a leisure craft that uses sails as its primary means of propulsion. A yacht may be a sail or power vessel used for pleasure, cruising, or racing. There is no standard definition, so the term applies here to sailing vessels that have a cabin with amenities that accommodate overnight use. To be termed a "yacht", as opposed to a "boat", such a vessel is likely to be at least 33 feet (10 m) in length and have been judged to have good aesthetic qualities. Sailboats that do not accommodate overnight use or are smaller than 30 feet (9.1 m) are not universally called yachts. Sailing yachts in excess of 130 feet (40 m) are generally considered to be superyachts.

Caribbean Sailing Yachts (CSY) is a company which built heavy-displacement recreational sailboats built during the 1970s and 1980s in Tampa, Florida. CSY was one of the first companies to recognize the impending growth of the Caribbean charter industry and although the company went out of business in the early 1980s, the well-founded boats have continued to sail the world's oceans for the past four decades. CSY's unique script logo was imprinted on a brass companionway medallion, dishware, and trailerboard design.

This article lists the largest active privately owned single-masted monohulls in excess of 130ft (39.6m) in overall sparred length.

Palari (boat) Type of Indonesian sailing vessel from South Sulawesi

Palari is a type of Indonesian sailing vessel from South Sulawesi. It was mainly used by the people of Ara and Lemo Lemo, for transporting goods and people. This vessel is rigged with pinisi rig, which often makes it better known as "Pinisi" instead of its name. In Singapore, palari is known as "Makassartrader".

The Com-Pac 23 is an American trailerable sailboat that was designed by Clark Mills as a pocket cruiser and first built in 1978. The boat has undergone design changes over time resulting in a series of improved models.

References