Amanda Knapp
Ballast tanks are compartments within boats, ships or other floating structures that are used to hold water. They are used to provide hydrostatic stability, reduce or control buoyancy, correct trim or list, and provide a more even load distribution along the hull. Ballast tanks are used in submarines, semi-submersible vessels, platforms, and SWATHs. They are also used in dry docks to sink the decks below the water level, enabling vessels to be moved into position for docking.
| Characteristics | Values |
|---|---|
| Purpose | To provide hydrostatic stability for a vessel, to reduce or control buoyancy, to correct trim or list, to provide a more even load distribution along the hull to reduce structural hogging or sagging stresses, or to increase draft |
| Function | Water is held in the ballast tank to provide weight adjustment, making it easier for the crew to reduce a vessel's draft when it enters shallower water, by temporarily pumping out ballast |
| Use cases | Submarines, semi-submersible vessels, platforms, SWATHs, wakeboard-specific inboard-engine boats, floating dry docks, floating boat lifts, caisson gates in dry dock and lock operations |
| Configuration | Typically a three-tank system with a tank in the centre of the boat and two more in the rear of the boat on either side of the engine compartment |
| Control | Ballast tanks are controlled from the helm with rocker switches |
| Upgrades | Wakeboard boat factory ballast systems can be upgraded with larger capacities by adding soft structured ballast bags |
| Emergency blow capability | HP air stored in flasks can be used to rapidly expel water from the ballast tanks, causing the boat to surface |
What You'll Learn
Ballast tanks can be used to sink a boat
In submarines, ballast tanks are used to submerge the vessel. When the submarine needs to surface, the boat will drive near the surface and then start a low-pressure blower to blow air into the ballast tanks and force the water out.
In wakeboard boats, ballast tanks are used to increase the draft of the boat and lower the centre of gravity.
Floating dry docks also rely on ballast tanks to sink their decks below the water level, enabling vessels to be moved into position for docking.
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Ballast tanks can be used to make a boat rise
In submarines, when the boat needs to surface, the crew will drive near the surface and then start a low-pressure blower to blow air into the ballast tanks and force the water out. This makes the boat rise. There is also an emergency blow capability using HP air stored in flasks. This air will rapidly expel the water from the ballast tanks, causing the boat to rise to the surface.
In floating dry docks, ballast tanks are used to sink the decks below the water level, enabling vessels to be moved into position for docking. Once secured, the ballast is discharged, lifting both the dock and the vessel above the waterline.
In larger ships and smaller wakeboard boats, adding water ballast to the tanks increases the draft of the boat and lowers the centre of gravity.
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Ballast tanks can be used to stabilise a boat
Ballast tanks are particularly useful for submarines, which need to be able to submerge and surface. When a submarine submerges, the vents at the top of the ballast tanks are opened and it sinks. To surface, the boat will drive near the surface, then start a low-pressure blower to blow air into the ballast tanks and force the water out.
Ballast tanks are also used in wakeboard-specific inboard-engine boats, which have multiple integrated ballast tanks that are filled with water by ballast pumps controlled from the helm with rocker switches. The hull of these boats has a lower centre of gravity, and the draft of the boat is increased.
Floating dry docks also rely on ballast tanks to sink their decks below the water level, enabling vessels to be moved into position for docking.
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Ballast tanks can be used to make a boat more manoeuvrable
Ballast tanks are particularly useful for submarines, which need to be able to submerge and surface. When a submarine submerges, the vents at the top of the ballast tanks are opened and it sinks. To surface, the boat will drive near the surface and then start a low-pressure blower to blow air into the ballast tanks and force the water out.
Ballast tanks are also used in floating dry docks to sink their decks below the water level, enabling vessels to be moved into position for docking. Once secured, the ballast is discharged, lifting both the dock and the vessel above the waterline.
In wakeboard-specific inboard-engine boats, ballast tanks are used to fill the hull with water, lowering the centre of gravity and increasing the draft of the boat. This makes the boat more stable and easier to manoeuvre.
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Ballast tanks can be used to dock a boat
Most wakeboard-specific inboard-engine boats have multiple ballast tanks that are filled with water by ballast pumps controlled from the helm with rocker switches. Typically, there is a tank in the centre of the boat and two more in the rear, on either side of the engine compartment.
Submarines use ballast tanks to submerge and surface. When the submarine submerges, the vents at the top of the ballast tanks are opened and it sinks. To surface, the boat will drive near the surface and start a low-pressure blower to blow air into the ballast tanks and force the water out.
Floating dry docks also rely on ballast tanks to sink their decks below the water level, enabling vessels to be moved into position for docking. Once secured, the ballast is discharged, lifting both the dock and the vessel above the waterline.
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Frequently asked questions
Ballast tanks are compartments within a boat, ship or other floating structure that hold water, which is used as ballast.
Ballast tanks are used to provide hydrostatic stability for a vessel, to reduce or control buoyancy, to correct trim or list, to provide a more even load distribution along the hull to reduce structural hogging or sagging stresses, or to increase draft.
When the submarine submerges, the vents at the top of the ballast tanks are opened and it sinks. To surface, the boat will drive near the surface then start a low-pressure blower to blow air into the ballast tanks and force the water out.
Ballast tanks are used to sink floating dry docks so that vessels can be moved into position for docking. Once secured, the ballast is discharged, lifting both the dock and the vessel above the waterline.
Ballast tanks are used to increase the draft of the boat. Most wakeboard-specific inboard-engine boats have multiple integrated ballast tanks that are filled with water by ballast pumps controlled from the helm with rocker switches.
