Heeling (sailing) in the context of "Windward and leeward"

A catamaran (/ˌkætəməˈræn/) (informally, a "cat") is a watercraft with two parallel hulls of equal size. The wide distance between a catamaran's hulls imparts stability through resistance to rolling and overturning; no ballast is required. Catamarans typically have less hull volume, smaller displacement, and shallower draft (draught) than monohulls of comparable length. The two hulls combined also often have a smaller hydrodynamic resistance than comparable monohulls, requiring less propulsive power from either sails or motors. The catamaran's wider stance on the water can reduce both heeling and wave-induced motion, as compared with a monohull, and can give reduced wakes.

Catamarans were invented by the Austronesian peoples, and enabled their expansion to the islands of the Indian and Pacific Oceans.

In geography and seamanship, windward (/ˈwɪndwərd/ WIND-wərd, /ˈwɪnərd/ WIN-ərd) and leeward (/ˈliːwərd/ LEE-wərd, /ˈljuːərd/ LEW-ərd) are directions relative to the wind. Windward is upwind from the point of reference, i.e., towards the direction from which the wind is coming; leeward is downwind from the point of reference, i.e., along the direction towards which the wind is going.

The side of a ship that is towards the leeward is its "lee side". If the vessel is heeling under the pressure of crosswind, the lee side will be the "lower side". During the Age of Sail, the term weather was used as a synonym for windward in some contexts, as in the weather gage.

The weather gage (sometimes spelled weather gauge or known as nautical gauge) is the advantageous position of a fighting sailing vessel relative to another. The concept is from the Age of Sail and is now antique. A ship at sea is said to possess the weather gage if it is in any position upwind of the other vessel -- having the wind at their back, speeding progress, when sailing towards the other ship. Proximity with the land, tidal and stream effects and wind variability due to geography (hills, cliffs, etc.) may also come into play.

• An upwind vessel is able to manoeuvre at will toward any downwind point, since the relative wind then moves aft.
• The fastest point of sail for a frigate typically have the wind blowing in the direction of travel, allowing that ship greater choice in the distance of separation. They could more easily disengage if damaged, and could more easily optimize for the range of their gunnery.
• However, in sailing warfare, the leeward ship gained a point of advantage in gunnery under heavier wind. When beating to windward, the vessel experiences heeling under the sideward pressure of the wind. This restricts gunnery, as cannon on the windward side are elevated, while the leeward gun ports aim into the sea or in heavy weather may be awash.
• Ships seeking to evade capture or attack have the advantage being downwind if they are faster vessels or are close to friendly land -- but in heavier weather a strong disadvantage if there is danger of grounding on a lee shore
• A vessel downwind of another, in attempting to attack upwind, is constrained to trim sail as the relative wind moves forward and cannot point too far into the wind for fear of being headed. The helm is typically more responsive on a downwind course. Sailing upwind involves frequent changes of sail: more tiring for the crew, more chance for mishap, and more taxing for the helm.
• A ship with the weather gage, turning downwind to attack, may alter course at will to bring starboard and port guns to appropriate elevations.

The term has had a literary rebirth in the popular seafaring novels of C.S. Forester, Patrick O'Brian and Alexander Kent. One of the last times that weather gage was perhaps a factor in a surface naval engagement was in the Battle of the Denmark Strait in 1941, where the German battleship Bismarck and the heavy cruiser Prinz Eugen held the weather gage over the British battleship HMS Prince of Wales and the battlecruiser HMS Hood. Being upwind, the German ships had the advantage that their rangefinders were drier than the British rangefinders facing the spray. The weather restricted the visual range to much less than the gun range.

Ballast is weight placed low in ships to lower their centre of gravity, which increases stability (more technically, to provide a righting moment to resist any heeling moment on the hull). Insufficiently ballasted boats tend to tip or heel excessively in high winds. Too much heel may result in the vessel filling with water and/or capsizing. If a sailing vessel needs to voyage without cargo, then ballast of little or no value will be loaded to keep the vessel upright. Some or all of this ballast will then be discarded when the cargo is loaded.

If a cargo vessel (such as a tanker, bulk carrier or container ship) wishes to travel empty or partially empty to collect cargo, it must travel "in ballast". This keeps the vessel in trim and keeps the propeller and rudder submerged. Typically, being "in ballast" will mean flooding ballast tanks with sea water. Serious problems may arise when ballast water is discharged, as water-borne organisms can create havoc when deposited in new environments.

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

Generally speaking, the wider the beam of a ship (or boat), the more initial stability it has, at the expense of secondary stability in the event of a capsize, where more energy is required to right the vessel from its inverted position. A ship that heels on her beam ends has her deck beams nearly vertical.