Breakwater(ship)

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Breakwater

Small delta, plate

Breakwaters on vessels serve as protection for cargo stowed forward, deck equipment, or similar structures which may be at risk of damage from green water. They consist of a low, exposed bulkhead on the forecastle or bow of a vessel. Breakwaters are also used to limit the aftward progression & volume of green water taken over the bow on wet ships. Freeing ports or open railings should be aligned with the aftward extent of the breakwater, allowing deflected water to run off the deck.

Contents

Design

Types

Delta

Delta Breakwater of USS Missouri demonstrating construction details

Delta, vee or V breakwaters, extend aftward from the centreline on either side, forming a 'V' when viewed from above. Typically, they are vertically tapered as they extend aftward. To deflect water away and outwards, delta breakwaters are angled forward. Where space is limited, the breakwater may only cant forward over the top portion of the structure (a vertical wall breakwater).

Double Skin

Double-skin breakwater (in red) on bow of Maersk vessel

Doubleskin breakwaters use two surfaces to dissipate water energy into the ships structure. The forward barrier can also be perforated to reduce loading. Doubleskin breakwaters are often used where vertical heights required are high, such as for crew passages or in way of container stacks.

Vane

Vane-style breakwater

Vane breakwaters consist of a number of short, vertical slats, transversely angled, within a frame. Vane type breakwaters prevent breaking water from collecting in front of the structure and spilling over and thus experience lower wave induced loading for the same level of protection. They also allow for crew movement between the slats fore & aft. Vane types, however, can't be taken to the deck edge and provide no personnel protection outside the apex as water still passes through to the deck aft.

Whaleback

A whaleback deck or breakwater consists of a highly cambered canopy over the uppermost deck forward, sloped aftward in profile (fore-aft) view. Whaleback's provide highly effective breaking of water, for minimal weight, as well as additional benefits to ship motions. A whaleback deck however is better incorporated into the design - i.e., as the covering deck of an enclosed moorage area. Retrofitted whalebacks make for difficult structural integration due to limiting angles and minimal headroom to work deck fittings.

Positioning

Breakwaters are typically placed as far aft as possible (to minimize required height), and as required to prevent damage or reduce scantlings of deck structures.

Loading

Loading varies with the amount of water taken, the velocity of impact (a combination of ships speed and waves speed), and the shape of the breakwater. An FPSO, which is often moored semi-statically or about its turret, will have much lower speeds than a high-speed container ship. Consideration should be taken of the vertical and horizontal loads and their translation into the deck structure.

External links

  • ASME CFD Evaluation [1]
  • Load Evaluation [2]
  • Greenwater on FSPO's [3]
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