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would add any stability, the water serves to displace air from the bottom of the hull; adding water ballast below the vertical center of gravity increases stability. The water ballast does not need to be lifted above the waterline to affect stability, as any material having greater bulk density than air will have an effect on the centre of gravity. It is the relationship between centre of gravity and centre of buoyancy that dictates the righting moment.
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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.
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A 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 speed through the water
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A common type of ballast for small boats that avoids many of the problems of high-density ballast is water ballast. While it may seem counter-intuitive that placing water in the hull (which is, after all, close to the same density as the water outside the hull – fresh vs salt water)
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that is deployed when the keel is tilted, and retracted (to reduce drag) when the keel is returned to the vertical. Some canting keels are designed so that when fully extended to either side they have an angle of attack of about 5° allowing the hydrofoil effect of the blade to lift the boat up and
410:. These materials often include non-native, nuisance, and exotic species that can cause extensive ecological and economic damage to aquatic ecosystems, along with serious human health issues including death. Although similarly harmful to the environment, ballast water discharge is different than
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Cruise ships, large tankers, and bulk cargo carriers use a huge 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. Ballast water discharge
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If a cargo vessel (such as a tanker, bulk carrier or container ship) wishes to travel empty or partially empty to collect a 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
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There are disadvantages to using high-density ballast. The first is the increased mass of the boat; a heavier boat sits lower in the water, increasing drag when it moves, and is generally less responsive to steering. A heavier boat is also more difficult to put on a
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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.
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or the weight of the boat (e.g. for transport on ground) and water added back in (in small boats, simply by opening up the valves and letting the water flow in) after the boat is launched or cargo unloaded. Pumps can also be used to empty the
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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.
248:. 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.
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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
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While prohibited by most class racing rules, some cutting-edge boats use a bulb of ballast on a long, thin keel that can tilt from side to side to create a
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387:, since its entry into force in September 2017. It is also controlled through national regulations, which may be separate from the Convention, such as
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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.
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and tow behind an automobile. Secondly, since the ballast needs to be as low as possible, it is often placed into a
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tank as the boat tacks, and the quantity of ballast can be varied to keep the boat at the optimum angle of heel.
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is discharged, as water-borne organisms can create havoc when deposited in new environments.
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Diagram showing the water pollution of the seas from untreated ballast water discharges
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to increase propeller immersion, to improve steering, and to control trim and draft.
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The advantage of water ballast is that the tanks can be emptied, reducing
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is so-called "live ballast", or the weight of the crew. By sitting on the
449:"Cruise Ship Pollution: Background, Laws and Regulations, and Key Issues"
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or retracting keel, requiring a heavy-duty mechanism to lift the massive
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typically contains a variety of biological materials, including
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One of the functions of a yacht's keel is to provide ballast.
481:. Lists general information and resources for ballast water.
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reduce wetted surface area for an increase in boat speed.
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On more advanced racing boats, a wire harness called a
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discharges by ships can have a negative impact on the
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A cargo ship discharging ballast water into the sea.
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479:United States National Agricultural Library
354:Ballast water discharge and the environment
195:The simplest form of ballast used in small
335:discharging ballast water before departure
339:On empty cargo vessels water is added to
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385:Ballast Water Management Convention
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455:(Updated February 6, 2008).
447:report: Copeland, Claudia.
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