Ships – Building – Freighters
Patent
1996-02-05
1997-09-09
Avila, Stephen
Ships
Building
Freighters
B63B 2503
Patent
active
056645147
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a tanker for carrying a liquid bulk cargo such as (crude) oil and the like or for carrying different liquid products.
In present tanker design, swash bulkheads are fitted in liquid bulk cargo tanks in order to reduce structural damage caused by wave motions inside a cargo tank, in particular in partially filled conditions ("swash" means: slosh, bubble, burble, wash).
Generally a swash bulkhead is fitted at approximately half the length (breadth) of a cargo tank and allows "through-flow" of the cargo and thereby prevents hydrostatic loading.
Depending on the variety of different cargo fillings and tank shapes one of the following versions of bulkheads will be applied: holes are spread across the total surface area; wherein the lower part is open; and upper part is open.
It will be appreciated by those skilled in the art that a conventional total swash bulkhead (full swash type) will have (large) holes spread across the total area, but at least one (limber) hole near the top and at least one (limber) hole near the bottom in order to prevent unintended hydrostatic loading (in case of operational errors or malfunctioning) and/or for draining purposes (bottom).
Swash bulkheads function a) by damping the surface (wave) movements of the cargo during movements of the vessel in sailing conditions (this is achieved by creating turbulence in the flow by means of sharp edges or holes), and b) by preventing wave resonance of the cargo by altering the (critical) tank length and/or breadth ratio (this is achieved by reflecting waves by means of a closed surface).
Known full swash type bulkheads contain a large number of holes spread over the total bulkhead area in order to damp the fluid movements in the tank and to allow a proper flow during normal cargo operations. The bulkhead structure is relatively light (thin plates and stiffeners) because no hydrostatic loading occurs.
In general, this construction performs properly. However, due to disasters with (crude) oil carriers and their large pollutional effect, a world-wide effort is made to improve the safety of tankers and nowadays there is an increasing need to construct tankers in such a way that in case of wreck or other marine catastrophe leakage of cargo and thus environmental pollution is avoided or minimized.
A solution for this problem is requiring a complete double hull for oil tankers (see e.g. DE-A-2158020) and for that purpose tankers have been built in the past with double bottoms and double sides, which, however, brought about substantial increases in the prices of tankers.
Further, double bottom constructions have the drawback that buoyancy loss in groundings may occur and in case the bottom of a cargo tank is penetrated due to corrosion and/or erosion, cargo may leak into the double bottom and generate a hazardous mixture of air and hydrocarbonaceous vapours, in case for instance oil is the cargo. Apart from the potential danger of explosion, there is the requirement for gas detection and thorough ventilation of the double bottom before entry for routine structural inspections.
Moreover, access to a double bottom also causes a problem. It must be through a vertical shaft or double side which is led right up to the deck. Other concerns include the maintenance of the steel structure in double bottoms, in particular preservation of the large coating area which is required for the prevention of corrosion. Further, double hull structures only provide adequate protection in case of low energy collisions.
Therefore, many organizations question the double hull as the best solution for pollution prevention and there is a need for alternatives provided that they offer the same level of protection against cargo outflow as the double hull tanker.
Another swash type bulkhead is disclosed by U.S. Pat. No. 3,164,120, which forms the basis for the preamble of claim 1. The location, the shape and the size of the openings in the bulkhead is determined only by considerations of (roll) stabilisation and strutural rigidity of the ship.
From F
REFERENCES:
patent: 3164120 (1965-01-01), Field
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