RIASSUNTO
Abstract
Industrial class vessels (offshore supply boats, tugs, and fishing vessels) have experienced stability problems during the last two decades. Many of these vessels are of similar hull form, including hard chins, a shallow-depth transom stern and large beam/length ratios. Existing stability criteria (U.S. Coast Guard or IMCO) involve static or quasi-static calculations of vessel stability with little regard to vessel dynamics.
To perform model tests and record vessel dynamics under various sea conditions, a capability for ""natural environment"" model testing has been developed at the University of Washington. Test instrumentation includes a Mobile Wave Measuring Platform and a suite of instruments for motion response measurement of free-running radio-controlled models. Tests are conducted on a large lake which adjoins the campus. The experimental set-up is described.
This paper presents the results of a series of tests of an eight-foot industrial vessel model. The tests were performed for varying wave conditions, vessel loadings and VCG positions, speeds and headings. The model is designed to survive capsizing. Six degree of freedom motion data are recorded to the limit of the gimbals used on the vertical gyroscope. Additionally, some wave data at the time of the tests are recorded. The results of the tests are presented and discussed.
Introduction
During the past decade, the marine industry saw the rapid development and greatly expanded use of industrial vessels. Included in this class of vessels are offshore supply boats, ocean-going tugs and fish boats. These vessels have been characterized by single or double chine hulls, deckhouse forward, long, shallow-depth transom sterns and a large open working deck aft. These vessels generally are between 70 and 120 feet in length, although longer vessels of this type can be found. Stability problems were and still are encountered in a number of applications of vessels of this design most notably offshore supply boats (especially when carrying pipe), king crab fish boats and some ocean-going tugs. A number of empirical and theoretical studies have produced stability criteria whose application has reduced the incidence of stability casualties. (1,2,3,4,5,6) Despite these advances, the mechanics of capsizing and its ,relationship-to roll motions in a seaway are still not understood.
The University of Washington Ocean Engineering Program has begun basic research aimed at recording and analyzing motion data of an industrial class vessel in a seaway. The model is a 1:11 scale model of an industrial vessel hull form, on loan from the. U.S. Coast Guard after its use in a major stability study performed for the Coast Guard by Hydromantic.(4)
Natural Environment Testing
Lacking towing tank facilities suitable for stability model testing in waves, University of Washington researchers turned to readily available local testing sites, Puget Sound and Lake Washington. The model was developed into a remotely controlled, self-propelled model, capable of recording data for motions in all six degrees of freedom. Wave data can be measured using a homemade, semi-submersible, platform. Together with suitable data recording and analyzing hardware and software, a complete natural environment test facility has been assembled.