Waterline length

A vessel's waterline length (abbreviated to LWL)[1] is the length of a ship or boat at the level where it sits in the water. The LWL will be shorter than the length of the boat overall (LOA) as most boats have bows and stern 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 LWL it is measured from a default load condition.

This measure is significant in determining a 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, without increasing beam or draft. Greater beam and draft produces a larger wetted surface, thereby causing higher hull drag. A boat's maximum speed, also known as theoretical hull speed, can be calculated using the formula: Vmax (in knots) = square root of LWL (in feet) x 1.34.

LOA (Length Overall) & LWL (Waterline Length)
Ship length measurements
Detailed hull dimensions

See also


  1. ^ Note: originally Load Waterline Length
  • Hayler, William B.; Keever, John M. (2003). American Merchant Seaman's Manual. Cornell Maritime Pr. ISBN 0-87033-549-9.
  • Turpin, Edward A.; McEwen, William A. (1980). Merchant Marine Officers' Handbook (4th ed.). Centreville, MD: Cornell Maritime Press. ISBN 0-87033-056-X.

C is the third letter in the English alphabet and a letter of the alphabets of many other writing systems which inherited it from the Latin alphabet. It is also the third letter of the ISO basic Latin alphabet. It is named cee (pronounced ) in English.


A catboat (or cat boat) is a sailboat with a single sail on a single mast set well forward in the bow of the boat. Most have a shallow draft, with centreboards, although some have a keel.Most are gaff rigged but some have a Bermuda rig. The beam of the classic Cape Cod Cat's beam measurement is almost half the waterline length, making it very stable.

Some cat boats in current use include the Beetle Cat, the Redden Catboat, the Nonsuch, the Inland Cat, the Zijlsloep. the Cape Cod Cat Com-Pac Trailerable, Marshal Menger, and the APBY cat boat.A catboat is not the same as a catamaran, which is a twin-hull boat. Nor is it the same as a Cat, a Norwegian ship used to carry up to 600 tons of coal.

Crater-class cargo ship

Crater-class cargo ship is a category of EC2-S-C1 type liberty ship freighters constructed by the United States Maritime Commission for use by the U.S. Navy during World War II. The designation 'EC2-S-C1' was composed of 'EC' (for Emergency Cargo), '2' (for a ship between 400 and 450 feet (120 and 140 m) long (Load Waterline Length)), 'S' (for steam engines), and 'C1' for a Type C1 ship.

The class was named for the lead ship of its type, USS Crater (AK-70). Its 62 hulls was the largest among U.S. Navy cargo ship classes.

The ships were propelled by a reciprocating steam engine using a single screw with a power of 1,950 hp (1,454 kW) shaft.

Hull speed

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.

From a technical perspective, at hull speed the bow and stern waves interfere constructively, creating relatively large waves, and thus a relatively large value of wave drag. Though the term "hull speed" seems to suggest that it is some sort of "speed limit" for a boat, in fact drag for a displacement hull increases smoothly and at an increasing rate with speed as hull speed is approached and exceeded, often with no noticeable inflection at hull speed.

The concept of hull speed is not used in modern naval architecture, where considerations of speed-length ratio or Froude number are considered more helpful.

Hunter 27

The Hunter 27 is a series of American sailboats, that were first built in 1974.The boat was built by Hunter Marine in the United States, but it is now out of production.

MacGregor 26

The MacGregor 26 is an American trailerable sailboat, that was designed by Roger MacGregor and first built in 1986, with production ending in 2013.The boat was built by MacGregor Yacht Corporation in the United States.The design was developed into the Tattoo 26, which remains in production by Tattoo Yachts.

Moorings 335

The Moorings 335 is an American sailboat that was designed for Moorings Yacht Charter and first built in 1988.The Moorings 335 is a development of the Hunter 33.5 specially for the charter market, with a shorter length overall, but longer waterline length and lighter displacement.

Sanibel 18

The Sanibel 18 is an American trailerable sailboat, that was designed by Charles Ludwig, first built in 1982 and named for the Floridian town and island.The boat was built by a series of different builders under a several different model names in the United States, but all are now out of production.

Ultra light displacement boat

An ultra light displacement boat (or ULDB) is a modern form of watercraft with limited displacement relative to the hull size (waterline length).

ULDBs are competitive, even after 35 years with open ocean racing participation and podium finishes even today. The relative low cost to obtain, tough construction and readily easy modifications make an Olson or a Hobie an extremely competitive and fun boat. The boats do lack comfort, and are not designed for cruising; however, with multiple transpac races, and multiple Bermuda 1-2 entries, they are proving to be a stalwart competitor despite their older design.


The waterline is the line where the hull of a ship meets the surface of the water. Specifically, it is also the name of a special marking, also known as an international load line, Plimsoll line and water line (positioned amidships), that indicates the draft of the ship and the legal limit to which a ship may be loaded for specific water types and temperatures in order to safely maintain buoyancy, particularly with regard to the hazard of waves that may arise. Varying water temperatures will affect a ship's draft; because warm water is less dense than cold water, providing less buoyancy. In the same way, fresh water is less dense than salinated or seawater with the same lessening effect upon buoyancy.

For vessels with displacement hulls, the hull speed is determined by, among other things, the waterline length. In a sailing boat, the waterline length can change significantly as the boat heels, and can dynamically affect the speed of the boat.

The waterline can also refer to any line on a ship's hull that is parallel to the water's surface when the ship is afloat in a normal position. Hence, all waterlines are one class of "ships lines" used to denote the shape of a hull in naval architecture plans.

In aircraft design, the term "waterline" refers to the vertical location of items on the aircraft. This is (normally) the "Z" axis of an XYZ coordinate system, the other two axes being the fuselage station (X) and buttock line (Y).

Winkle Brig

16 ft (4.9 m) gaff rig pocket cruiser built between 1985 and 2002. Approximately 122 were built before production ceased.

Designer: Eric Bergqvist

Builders: Ferry Boatyard, Cheshire, England

Length on deck: 16 ft (4.9 m)

Length overall: 20 ft (6.1 m)

Waterline length: 15 ft (4.6 m)

Beam: 6 ft 8 in (2.03 m)

Draught: 1 ft 2in / 2 ft 6in (twin retractable bilge boards)

Displacement': 650 kgSails:

Main 104 sq ft (9.7 m2)

Jib 42 sq ft (3.9 m2)

Topsail 26 sq ft (2.4 m2)


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