Calculation of ship collision avoidance manoeuvres: A simplified approach

The moment at which in a two-ship encounter a collision avoidance manoeuvre should be initiated in order to achieve a specific distance at the closest point of approach has been calculated. The calculations were based on the kinematics of encounter and simplified equations of motion. Mathematical equations which relate the maneouvring distance, the turning direction and the extent of course change for any desired passing distance and any given turning rate are determined. Knowledge of these quantities is essential for the safe conduct of the ship with automatic, computer-assisted navigation as well as with ordinary, manual navigation if the navigator no longer contents himself with estimates but wishes to know precisely in advance the outcome of any specific manoeuvre he chooses.     

Regional tectonic trends on the inner continental shelf off Konkan and Central West Coast of India

Satellite imagery and offshore magnetic data were analysed to correlate regional tectonic elements on the inner continental shelf off Konkan and the adjacent Deccan plateau. Three statistically important lineament trends—N-S, WNW-ESE and ENE-WSW—that prevail on land are correlatable well with the offshore trends. This positive correlation suggests simultaneous deformation. The major magnetic lineament observed off Jaigad Bay, west coast of India, may be the extension of onshore lineaments. The correlation of both the offshore and onshore trends indicates that the fracture pattern of the crystalline basement has also controlled the offshore structural pattern.     

Tectonics of short-offset,slow-slipping transform zones in the FAMOUS area,Mid-Atlantic Ridge

ANGUS photographs and ALVIN observational data from Fracture Zones A and B on the Mid-Atlantic Ridge near 37°N were examined for structural and sedimentological indications of the area's tectonics. Both transform fault zones are characterized by volcanic rubble, breccias, chalks, and undisturbed sediments typical of slow-slipping transforms.The photographic data consist of 16 camera-sled traverses from the FAMOUS Expedition using the ANGUS deep-towed camera system. These data cover several different morphotectonic provinces along the strike of both slow-slipping (2 cm yr^-1) fracture zones. ALVIN data come from two dives in the central part of Fracture Zone B. The two fracture zones differ in their distribution of fractured and sheared chalks which indicate regions of strike-slip deformation along the transform. Evidence of shearing is confined to a very narrow region in the center of FZ A, whereas the zone of shear deformation is as much as 6 km wide across FZ B. Other differences include the morphology and depth of the transform valleys and their contiguous nodal basins and the extent of exposures of fresh-looking volcanic ridges in the nodal basin.     

Changing coastal oceanography of the Black Sea II: Mediterranean effluent

This article describes the hydrography of the Northwestern Shelf (NWS), of the Black Sea emphasizing the changes induced by water management in the Dniejer and Dniester river basins. The existing literature and previously unpublished data have been reviewed and synthesized to describe water property fields and transport mechanisms of the NWS and the Dnieper and Dniester estuaries before the early 1960s, or the so-called precontrol period, when the effect of artificial river flow control upon the coastal waters was insignificant.After the hydroenergy complexes and water withdrawal and disposal systems on rivers became fully operational in the early 1970s (the so-called postcontrol period), the annual river discharge from the Dnieper and Dniester had noticeably decreased and seasonal river flow patterns had been artificially modified. Instead of a powerful and short early spring flood, typical for the natural conditions in the Dnieper river, the hydrographs in the postcontrol period exhibit two smaller peaks of river discharge of much longer period. One of them (winter-early spring) is caused by intense hydroenergy generation and weir discharges through the cascade of storage reservoirs. Another is associated with spring flood, modified by intense water consumption and storage in this period. High average river discharge in late May—early June strengthened the summer pycnocline which inhibits vertical mixing in the estuaries and coastal waters. Owing to a slow summer circulation, the rate of natural purification of the entire coastal system has been reduced. This coupled with the increased nutrient, organic and pollutant transport, decreased the dissolved-oxygen concentration and led to anoxic events and mass mortalities of marine organisms in the previously productive regions. These effects have primarily plagued the benthic communities along the entire western coast of the NWS since 1973.Winter convective overturn in the Black Sea reaches its maximum depth at the southern boundary of the NWS. Thus, the NWS waters descend beneath the seasonal and main thermoclines in the open sea and are spread by the prevailing currents across the entire sea in the cold intermediate layer (CIL). By this dynamic mechanism the projected man-made modifications in the riverine-estuarine systems of the NWS will affect and change the large-scale thermohaline structure and marine life of the Black Sea.     

Condition of coastal mesoplankton communities in the northeastern area of the Black Sea in 2005

The structure and distribution of mesoplankton in the northeastern part of the Black Sea along 6-mile and 100-mile sections in the area off Golubaya Bay (near the city of Gelendzhik) were analyzed. The studies were performed from R/V Akvanavt and the boat Ashamba. The observations were carried out during the vegetation season from the beginning of June to the first half of October 2005. Samples of mesoplankton were collected with use of a BSD net with an opening of 0.1 m² and a mesh size of 180 μm. Both the total (over the entire water column) and layer-by-layer (separately for the upper quasi-homogeneous layer, the seasonal thermocline, and the subthermocline layer) hauls were performed down to the bottom (at sea depths of less than 200 m) or down to the upper boundary of the hydrogen sulfide waters. The particular hydrophysical conditions that were observed in 2005 resulted in an approximately one-month advance of the phenological condition of the planktonic community as compared to the usual pattern. Beroe ovata appeared in the plankton at the end of July, the mass development of Mnemiopsis leidyi was suppressed, and the duration of its influence on edible zooplankton was essentially reduced. As a result, the total mesoplankton biomass in August–October 2005 was 1.5–2 times as great as that in 2004. The abundance of Acartia clausi increased approximately 4–5 times and the quantity of Sagitta setosa also considerably increased. At selected stations, Mnemiopsis leidyias, the main predator in the community, was replaced by Sagitta setosa.     

Equilibrium constants of triethanolamine in major seawater salts

Acid–base equilibrium constants of triethanolamine (TEA) have been determined by potentiometric titrations with a glass electrode, at 25 °C. Ionic strength was kept constant with only one electrolyte (using one of these salts: NaCl, KCl, MgCl₂ or CaCl₂), with binary mixtures of MgCl₂ and CaCl₂, and finally, in a solution with a composition approximately similar to that of natural seawater without sulfate. Equilibrium constants have been expressed in function of ionic strength by means of Pitzer equations and interaction parameters proposed in this theory have been obtained. It has been found that acid–base behaviour of TEA depends greatly on the salt used: basicity of TEA is decreased by CaCl₂, while it is increased by the other electrolytes used in this work.