Buoyancy

Buoyancy – Interaction between gravity (pushes down), and density of fluid, which pushes up. Density (D= m/v) of water is set at 1. >1, object sinks <1, object floats

The push of water pressure creates buoyancy. Air filling the inside assures that the density of the ship is < 1.

Weighted-based Stability Used for narrow- hull ships. Weight in the bottom of the hull is used as “ballast” to stabilize the hull.

Leveraged Stability A wide hull is used for stability.

Ship will right itself as Buoyancy pushes directly against the gravitational weight. Stiff ship – rights Itself very quickly. Tender ship – tend to be a little top heavy, which means that when it rolls one way it goes far that way, then rolls far the other way. Tends to rock back and forth.

Ship is in danger of capsizing because the weight on the right is increasing, while the buoyancy on the left is increasing as well, creating a tendency for the “heavy side” to push downward and the “more buoyant” side to push upward.

B B B G G G Note: As the weight shifts, so does buoyancy and gravitational force: Gravity pushes down on the side as weight increases. Buoyancy decreases and shifts away from gravity as the weight shifts. Eventually, water will pour in from the side or top and the ship will rapidly sink.

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Plimsoll Lines Show the maximum depth to which a ship can be safely loaded in different zones and seasons.

Load Lines Show the Depth to which the hull is riding in the water.

How stable can this ship be?

Buoyancy Control for divers Air tanks and air in lungs Leaded weight belt

Swim bladder

How does a Submarine Work?

Main Induction valve

Vents on top of the top of the ballast tanks are opened. Seawater enters through flood ports, forcing air out vents. Submerging a Submarine

Loss of Buoyancy -replacement of air volume by water. -Increases density from 1. -The result is that the ship is no longer less dense than water, but denser than sea water.

Oil Tankers- now built with double hulls to create a void space that could be pierced and flooded upon grounding, but leave undamaged the inner hull containing the petroleum products.

Watertight compartments To be effective, the compartments need to include the deck and ceiling, access being gained through hatches- This lack was a major factor in Titanic’s sinking.

Titanic had 15 watertight compartments. She was designed to stay afloat with up to 5 compartments flooded. However, she did not have tops to the compartments. Due to the puncture of 6 compartments, she filled like an ice cube tray.

Warships – built with extensive subdivisions and watertight compartments and dog hatches, but it isn’t always enough.

Sculpin was the first ship to reach the Sailfish sinking location.

Squalus, now the Sailfish. She was rebuilt and recommissioned and served throughout WW II, earning a Presidential Unit Citation.

Submarine Task Force Commander, USS Sculpin. Sculpin attack Japanese convoy and Suffered severe and accurate depth-charging and was force to surface. Losing a running gun battle with Japanese destroyers, Sculpin was scuttled. Capt. Crommell stayed on Board because he had informaton about the upcoming Gilbert and Marshall Island invasions. For this self-sacrifice, he was award the Medal of Honor, Posthumously.

Suviving crew of the Sculpin were to be transported to the Japanese home islands aboard the carrier Chuyo. During a severe storm, the Chuyo was successfully torpedoed by an American submarine, Sailfish. Only one american sailor survived the sinking of Chuyo.