Ballast is used in sailboats to provide moment to resist the lateral forces on the sail. In some cases less is more The purpose of this article is to give an overview In Physics, the moment of force (often just moment, though there are other quantities of that name such as Moment of inertia) is a Pseudovector A sail is any type of surface intended to generate Thrust by being placed in a Wind &mdashin essence a vertically-oriented Wing. Insufficiently ballasted boats will tend to tip, or heel, excessively in high winds. Too much heel may result in the boat capsizing. The common definition for capsized refers to when a Boat or Ship is tipped over until disabled When sailing vessels carried cargo, it was at times necessary to sail to a port with no cargo. In order to do this enough ballast of little or no value would be loaded to keep the vessel upright. This ballast would then be discarded when the cargo was loaded.

Uses

One of the functions of a yacht's keel is to provide ballast.

Ballast takes many forms. The simplest form of ballast used in small day sailers, is so-called "live ballast", or the weight of the crew. A day sailer or dayboat is a small Sailboat without sleeping accommodations but which is larger than a Dinghy. By sitting on the windward side of the hull, the heeling moment must lift the weight of the crew. Windward is the direction from which the wind is blowing at the time in question A hull is the body of a Ship or Boat. It is a central concept in floating vessels as it provides the Buoyancy that keeps the vessel from sinking On more advanced racing boats, a wire harness called a trapeze is used to allow the crew to hang completely over the side of the hull without falling out; this provides much larger amounts of righting moment due to the larger leverage of the crew's weight, but can be dangerous if the wind suddenly dies, as the sudden loss of heeling moment can dump the crew in the water. In Sailing, the trapeze refers to a wire that comes from a point high on the mast, usually where the shrouds are fixed to a hook on the crew member's harness On larger modern vessels, the keel is made of or filled with a high density material, such as concrete, iron, or lead. In boats and ships keel can refer to either of two parts a structural element or a hydrodynamic element The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly By placing the weight as low as possible (often in a large bulb at the bottom of the keel) the maximum righting moment can be extracted from the given mass. Traditional forms of ballast carried inside the hull were stones or sand.

High density ballast

There are disadvantages to using high density ballast. The first is the increased mass of the boat. A heavier craft accelerates slower than a lighter craft, and is generally less responsive to steering input. A heavier boat is also more difficult to put on a trailer and tow behind an automobile. A Trailer is generally an unpowered vehicle pulled by a powered vehicle Since the ballast needs to be as low as possible, it is often placed into a centerboard or retracting keel, requiring a heavy duty crank to lift the massive foil. centreboard is a retractable Keel which pivots out of a slot in the hull of a Sailboat, known as a centerboard trunk (US or case A foil is a surface designed to maximize lift (force generated perpendicular to the fluid flow while minimizing drag (force generated in the direction of the fluid The simplest solution is to use a fixed ballasted keel, but that makes the boat nearly incapable of sailing in very shallow water, and more difficult to place on a trailer. While prohibited by most class racing rules, some cutting edge boats use a bulb of ballast on a long, thin keel that can cant side to side to create a canting keel. A canting keel is a form of Sailing ballast, suspended from a rigid canting strut beneath the boat which can be swung to Windward of a boat under sail This lets the ballast be placed on the windward side, providing a far greater righting moment with a lower angle of heel. Tilting the keel, however, greatly reduces its lift, so canting keels are usually combined with a retractable centerboard or daggerboard that is deployed when the keel is tilted, and retracted (to reduce drag) when the keel is straight. A daggerboard is a retractable Keel used by various Sailing craft

Water ballast

A common type of ballast for small boats that avoids many of the problems of high density ballast is water ballast. While it seems illogical that placing water in the hull (which is, after all, the same density as the water outside the hull) would add any stability, in fact, adding water ballast below the vertical center of gravity increases stability. When the boat heels, it must then lift the ballast clear of the water, at which point it is obvious that it does provide righting moment. The advantage of water ballast is that it can be dumped out by having a valve at the bottom of the ballast chamber, reducing the weight of the boat for trailering, and then added back in by opening up the valves and letting the water flow in after the boat is launched. Pumps can also be used to empty the leeward ballast tank and fill the windward tank as the boat tacks, and the quantity of ballast can be varied to keep the boat at the optimum angle of heel. Windward is the direction from which the wind is blowing at the time in question Windward is the direction from which the wind is blowing at the time in question The disadvantage of water ballast is that water is not very dense and therefore the tanks required take up more space than other forms of ballast. Some manufacturers offer flexible ballast bags that are mounted outboard of the hull on both sides, and pumps that use the boat's velocity through the water for power. When under way, the pump can be used to fill the windward side, while the lee side is allowed to drain. This system, while not very attractive, does allow significant gains in righting force with no modifications to the hull.

A trick commonly used on boats with water ballast is to link port and starboard tanks with a valved pipe. When preparing to tack, the valve is opened, and water in the windward tank, which is higher, is allowed to flow to the lee side, and the sheet is let off to keep the boat from heeling too far. Once as much water as possible has been transferred to the lee side, the boat is brought about and the sail sheeted in, lifting the newly full windward tank. A simple hand pump can then be used to move any remaining water from the lee to the windward tank.

Ship's ballast

On cargo vessels water ballast is added to the ballast tanks when empty to increase propeller immersion, to improve steering, and to control trim and draft. A ballast tank is a compartment within a boat or ship that holds water The draft (or draught) of a ship's hull is the vertical distance between the Waterline and the bottom of the hull ( Keel) with the thickness

One disadvantage of water ballast in cargo vessels (which use ballast to maintain correct trim when not fully laden) is the dispersal of marine organisms, picked up with the water in one area and dumped with the ballast in another area. These alien organisms can then go on to cause significant damage in their new habitat and once established they can prove almost impossible to eliminate. Many smaller sailing vessels use water ballast to save weight and allow easy trailering, and the ballast is loaded at launching and dumped when the boat is re-trailered, usually at the same location.

Environmental issues

Main article: Ballast water discharge and the environment

Cruise ships, large tankers, and bulk cargo carriers use a tremendous amount of ballast water, which is often taken on in the coastal waters in one region after ships discharge wastewater or unload cargo, and discharged at the next port of call, wherever more cargo is loaded. Cruise ships large tankers and bulk cargo carriers use a tremendous amount of ballast water, which is often taken on in the coastal waters in one region Ballast water discharge typically contains a variety of biological materials, including plants, animals, viruses, and bacteria. These materials often include non-native, nuisance, exotic species that can cause extensive ecological and economic damage to aquatic ecosystems. Ballast water discharges are believed to be the leading source of invasive species in U. S. marine waters, thus posing public health and environmental risks, as well as significant economic cost to industries such as water and power utilities, commercial and recreational fisheries, agriculture, and tourism. ^[1] Studies suggest that the economic cost just from introduction of pest mollusks (zebra mussels, the Asian clam, and others) to U. S. aquatic ecosystems is more than $6 billion per year. ^[2]

In the United States, the National Invasive Species Act of 1996 is meant to control the invasion of aquatic nuisance species. The United States of America —commonly referred to as the

References

This article incorporates text from a public domain Congressional Research Service report: Copeland, Claudia. The public domain is a range of abstract materials &ndash commonly referred to as Intellectual property &ndash which are not owned or controlled by anyone The Congressional Research Service (CRS is the Public policy research arm of the United States Congress. "Cruise Ship Pollution: Background, Laws and Regulations, and Key Issues" (Order Code RL32450). Congressional Research Service (Updated February 6, 2008). The Congressional Research Service (CRS is the Public policy research arm of the United States Congress.