Steel Hull Research Articles

A MECHANICAL OYSTER HARVESTER FOR SOUTH CAROLINA ESTUARIES

ABSTRACTA mechanical oyster harvester has been developed for the intertidal oyster (Crassostrea virginica). The harvester is hydraulically powered and mounted on a 16 m steel hull vessel designed for its operation. The objective of this research was to produce a machine that would efficiently harvest oysters while doing minimum damage to the oysters and the fragile shell matrix that supports them. Results of three years' testing show harvest rates of 18 m3 /hour. Damage to the shell matrix was almost undetectable and damage to the harvested oysters was about 5%. The harvester can operate at depths of one to 3 m with the head controlled automatically. Bottom contact force is adjustable and regulated automatically during harvest to minimize bottom damage. The harvesting head can pitch or roll 0.35 rad to follow bottom contour. Future plans for the harvester include leasing to the L. P. Maggioni Oyster Company for commercial harvest during the 1982‐83 season. Eventually the harvester will be used by the state of South Carolina for oyster bed management and transplanting of oysters from polluted areas to public shellfish grounds.

Part III structural reliability assessment under internal and external load conditions

The classical reliability function is used as a risk criterion in the analysis of the containment of a PWR. For the treatment of the internal load case LOCA the probability of occurrence as well as the probability distribution of the load intensity are considered. In recognition of the rare event properties of the internal and external hazards the Poisson process is used as a forecast model. Consequently the asymptotic distributions of the Fisher-Tippett type are utilized to model the load intensities. The investigation concentrates on the analysis of the steel hull for which the governing external hazard of the earthquake is considered. As failure criteria yield and the fracture conditions are used.

A complex study on the reliability assessment of the containment of a PWR Parts I–III

The intention of this paper is to contribute to the development of methods to be used for the quantification of the risk of nuclear power plants. For this purpose a reliability analysis of a structural component, i.e. a reactor containment structure is carried out. Detailed information in various fields had to be developed and compiled. The project consists of three parts: Part I concentrates mainly on the analysis of the load condition of the steel hull following a Loss of Coolant Accident (LOCA). Part II deals with the material aspects of the design properties of containment steels and furthermore the behaviour of concrete under impact load conditions are discussed. Part III of the paper is concerned on the one hand with external load conditions, and on the other hand with assembling the information of the previous parts to a reliability analysis. The methodology is exemplified by applying the general and theoretical results to the containment of the PWR-plant “Biblis B”.

Noise prediction in ships

A research program has been organized by the Swedish Ship Research Foundation. One of the objectives of the program has been to develop a noise prediction method. In its first form this prediction method is of empirical type, based on extensive noise level and vibration measurements in three reference ships. It has the form of a computer program. Depending on ship type, somewhat different propagation models can be chosen. The vibration measurements in the reference ships reveal some of the fundamental difficulties in getting an accurate calculation method. The different stops in the calculation also have rather different accuracy. The radiation of sound from the linings can be accurately predicted; however, predicting the structure‐borne transmission in the steel hull and from the steel construction to the linings involve greater uncertainties. One of the reasons for this is the unexpectedly high level of inplane waves in the steel structure (longitudinal and transverse waves). [Compare to T. Kihlman and J. Plunt, “Structure‐borne sound in ships: Study of different waveforms,” ICA 8 (1974).]

The Investigation of an Unusual Cause of Shipbottom Pitting★

Abstract Two unusual and severe cases of shipbottom pitting were encountered within the space of a few years. Although the two incidents occurred in polluted harbors 3000 miles apart, the vessels involved showed the same symptoms. These symptoms were rapid pitting, inactivation of the blackened antifouling paint and good electrical conductivity of the black surface film. The black conversion product, found only in the upper layer of the antifouling paint, was shorted to the steel hull. A study of the painting history of the vessels involved and of the conditions to which they were exposed in service indicated two common factors were present on ships that pitted. First, there was contact between the antifouling paint and the steel hull and secondly, there was exposure to sulfide forming waters. When one of these factors was missing, vessels exposed to the other condition did not show unusual pitting. To confirm a theory as to the cause of pitting a series of test panels duplicating conditions experienced in service were prepared. The tests, with suitable controls tended to substantiate the theory advanced. From information so obtained it was possible to recommend simple measures that would prevent the recurrence of the severe underwater corrosion described.

Anomalous Inactivation of Heavy Metal Antifouling Paints*

THAT ordinarily effective antifouling paints occasionally show very poor performance, or suddenly begin to foul severely after a period of satisfactory functioning, is an observation familiar to every user of marine paints. In the case of compositions carrying metallic copper, such failures have been almost universally attributed to 'galvanic coupling' with the steel hull—the implication being strong that such paints can and do act in a manner entirely analogous to a gross sheet of copper. In an effort, therefore, to establish the real truth of this matter, the phenomenon of inactivation with both metallic copper and cuprous oxide paints has been under study by us for some time. We have already shown that accidental or deliberate contact of the steel hull with either type of copper-bearing paint can lead to serious pitting at the contact point and to accelerated corrosion attack at adjacent bare areas or 'holidays'1,2. An equally if not more serious result of failure to separate properly the antifouling paint from the steel hull by adequate barrier coats is a decreased effectiveness or even complete inactivation of the antifouling coat1.

Countering the Magnetic Mine

ACCORDING to the naval correspondent of The Times,a conspicuous feature of the Queen Elizabethon her arrival at New York after her secret maiden voyage from the Clyde was a ‘girdle’ around her hull. This girdle is apparently the means of protection adopted against the magnetic mine. The girdle, supplied with electric current of the necessary strength and characteristics, sets up a magnetic field which, in association with the steel hull and other magnetic material of the ship, is such that magnetic mines laid at sea are not set off by the passage over them of a vessel so equipped. The apparatus is said to have been devised and developed by officers of one of H.M. naval establishments, with the advice and assistance of scientific men consulted for the purpose. It has been given the expressive name ‘de-gaussing girdle’, the aptness of which will be recognized by all with an elementary knowledge of magnetism.

Economical Design of Hydraulic Pipe-Line Dredge

The hydraulic pipe-line dredge described in this paper3 is possibly the largest and most powerful built to date (1930) and embodies some new and novel equipment and construction features. It was designed for the Great Lakes and ocean service as well as for river work. The steel hull is made exceptionally heavy and rigid not only to withstand the machinery vibrations, but to support the dredge without failure if it sinks on an uneven bottom. The curved ends of the hull are the result of experiments to determine that shape which would require the minimum power for towing.