A New Type Marine Crane for Adverse Weather and Sea States
Authors: Hettinger Fredric L. 
Published: October 2008

Recent at-sea operations conducted by Ocean Systems, Inc. involving the launch and recovery of diving chambers and small submersibles have dramatically pointed out the shortcomings of traditional cargo handling equipment. Recognizing these problems, Ocean Systems, Inc. engineers, in conjunction with Mr. E. A. Link, Chief Marine Consultant, have developed a new type of marine crane for adverse weather and sea states. This new system is basically a hydraulic back-hoe machine modified to incorporate an articulating member equipped with patended fastreeving and load swing control mechanisms. A unique load attachment device is connected to the end of the lift wire which permits rapid load attachment.

The primary function of this new crane is to transfer a relatively large and vulnerable object from the surface of the sea or deck of a vessel to a floating or fixed platform. Since many of the operations conducted by Ocean Systems, Inc. involve the use of critically stressed man-rated structures all handling operations must be conducted with the-highest possible degree of safety and control.

Operational experience to date with the first production marine crane have been successful. Test loads up to 13,000 lbs. have been satisfactorily handled in sea conditions varying from dead calm to Sea State 5.

INTRODUCTION

Historical Background

During the recent accelerated growth of oceanic technology, and the ocean sciences in general, operating personnel have often noted the severe limitations of existing shipboard handling equipment Ocean Systems, Inc., in particular, in the course of its many at-sea operations, has been aware of this deficiency since the very beginnings of the company's activities. In addition to the usual stresses and requirements placed upon marine equipment (i.e. sea state dynamics, salt-water environment, etc.), the handling of a critically-stressed pressure vessel presents additional problems. A handling mishap can easily result in the destruction of the vessel's pressure integrity with a corresponding serious physiological effect on the crew. Fortunately, none of these serious accidents have occurred during past Ocean Systems operations. Several mishaps have occurred, however, during the handling of the submersible DEEP DIVER that have resulted in damage to fairings, transducers, external lights and miscellaneous components.

Specific Problem Areas

With this operational experience as a background, Ocean System' engineers defined specific problem areas that were inherent with typical Man-In-the-Sea mission. Primary in these critical areas is the requirement for maintaining positive control of the load during lunch and recovery. Since undesired load swing is clearly a function of the lift pendant length. Further requirements include maintaining edequate hull and topside clearances when the load is handled, particularly in heavy seas. The need for rapid retrieval was noted in conjunction with following sea damage and shock effects. As many of Ocean System' operation involved the submersible, DEEP DIVER, a mean for a rapid and safe cable attachment/detachment was required. In the deck placement of the DEEP DIVER, as well as the deck mating of Submersible Diving Chambers (SDC), a definite requirement existed for accurate load positioning. The need for precise "inching' capability was noted in conjunction with the deck compression chamber.