A Simplified Method of Calculating Propeller Parameters for Small Trawlers

It is quite common to encounter a propeller installed on a trawl that does not develop adaquate thrust to pull the trawl at a specified trawling speed. The immediate actions usually taken are to reduce the size of a trawl, change to a new propeller or install a higher powered engine. All these alternatives will impose a financial strain on the fishermen. Therefore, a simple method of calculation is being suggested to obtain a spectrum of propeller parameters such as diameter, pitch- diameter ratio, speed, quasipropulsive coefficient and propeller performance coefficient for a given engine model. The best combination of parameters can be obtained in order to satisfy a specific trawling requirement. Usually the requirement is stated in the form of thrust of propeller to overcome total gear drag at a specific trawling speed. Total gear drag can be determined by a model test or mathematical modelling. Three engine models have been studied and for each model values of thrusts, propeller performance coefficients and quasi- propulsive coefficient were calculated. Having known the values of torque coefficient (J.l) and advance coefficient (¢) the values of pitch- diameter ratios were obtained from propeller performance curve

Primary Productivity and Mineral Nutrient Status of some Estuarine and Coastal Waters along the East Coast of Peninsular Malaysia during the off Monsoon Period.

A study of the organic and inorganic mineral status, primary productivity and related environmental parameters of some estuarine and coastal waters along the east coast of Peninsular Malaysia indicates that the estuarine waters act as nutrient sources for the adjacent coastal waters. The net photosynthetic values at the estuarine stations ranged from 82.0-125.4 and 104.0-257.9 fJ.g C/1/h while that of coastal stations ranged from 42.0-164.5 and 66.0-198.2 fJ.g C/1/h during the high and low tides respectivelv. During the low tides, at both the estuarine and coastal stations, the dissolved organic nitrogen, particulate orgMlic phosphorus and inorganic ammonium nitrogen were present in high concentrations while that of dissolved oxygen, inorganic nitrate nitrogen and nitrite nitrogen were low throughout the study period