February 1977 - Maritime Reporter and Engineering News

SNAME San Diego Announces Site For 1980 Spring Meeting

The January meeting of the San Diego Section of The Society of Naval Architects and Marine Engineers was held at the Cafe Del Rey Moro in Balboa Park on January 19, 1977. Following an enjoyable dinner, a short business meeting was held in which it was announced that the proposed site of the Hotel Del Coronado for the 1980 Spring Meeting has been approved by National Headquarters.

David Pritchard, secretarytreasurer of the San Francisco Section, announced that they are hosting the 1977 National Spring Meeting, May 25 through 27, to be held at the Fairmont Hotel, and asked all who could to attend.

Ralph Bradford Jr., Section Papers chairman, introduced the evening's speakers, Thomas J.H.

Glassen and Wesley W. Hickman, both of National Steel and Shipbuilding Company. Their paper is entitled "A Method of Predicting Discharge Time of Cargo and Ballast Systems of Tankers." Mr. Hickman introduced the paper, which discussed the use of a computer program to determine cargo system performance.

The system described was that of a cargo and ballast pumping system, including the tanks and the pumps and all piping to the discharge manifold. The program performs the iterative process for solution of the numerous variables involved to determine the system performance at discrete time intervals.

It was pointed out that the often used method of sizing cargo pumps is to divide the cargo cubic by the desired pump out time. This neglects the required head at this volume rate, friction, rail pressure, and many other items. With this method, even after all calculations and layouts are made, the designer knows that he has a system that will pump a design quantity at a design head, but not much about the total time to empty the ship. The ability to closely predict the discharge time, especially on short runs, is of great value to the owner. The costsaving techniques in moving cargo from A to B, that have been the results of much study in optimizing tanker design, can be quickly offset or partially negated by turnaround time.

Mr. Glassen continued the presentation by discussing the program itself. The program uses the PROSE computer language and after the initial setting up of the problem, which requires significant effort, performs the necessary calculations at set time intervals. The computer assumes a tank flow rate and iterates through the friction losses, pressure, and other constraints to assure all are satisfied, or changes the rates until they are satisfied.

As the tanks empty, the program adjusts discharge rate by reducing pump speed to maintain the NPSHA above the NPSHR, thus maximizing the output. When the pump speed falls below 80 percent, the program begins discharge throttling until the tanks are empty. The output of the program is a time history of the calculated values and tank fluid level. The program once set up can be readily used as a design tool to investigate variations in system parameters and mediums to be discharged.

A lively discussion followed in which additional information on the commercially available PROSE computer language was mentioned and its usefulness in this type of application explained.

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