There was a need for a lightweight hydrocrane to handle launching and recovery of the Harbor Branch Foundation submersible, JOHNSON-SEA-LINK. Aluminum, because of its high strength to weight ratio, weldability, high corrosion resistance and low maintenance became the prime candidate for this application, all of which led Edwin A. Link, Trustee and Vice President of Harbor Branch Foundation, Inc. to request the assistance of ALCOA in the design of a suitable unit.
Specifications called for launching or recovery of the vehicle off the stern of the mothership, R/V JOHNSON, in twenty-five seconds or less under sea state five (5) conditions. Safety further dictated that a connecting device be devised to minimize the time the submersible was in the water adjacent to the mothership. Another important requirement was damping the pendulum motion of the vehicle during launching and. recovery.
The resulting design incorporates a two axis hydraulic spot-disc brake system which reduced the handling problem to a safe level. A novel fail safe "drop lock" device for connecting the crane and submersible was developed by Harbor Branch foundation to aid the launching operation without requiring swimmers to be in the water, and only one swimmer for recovery with considerably reduced hazards.
Specifications, loads, stresses, hydraulic circuits and other design criteria are given in the paper.
One of the inherent problems of launching and recovering a submersible from the deck of a surface vessel in heavy seas is to accomplish the task as fast and safely as possible. With this prerequisite in mind, Mr. E. A. Link embarked on a program of developing a crane to accomplish this task. Depending on the sea conditions and the direction of the ship and submersible with the wind, there are times when the vessel and vehicle are in and out of phase. There are two methods of hoisting a vehicle from the water, one is to employ a mechanism to pay in or payout the hoist line keeping a constant pre-set tension on the line. Another, is to hook up and virtually snatch the vehicle from the water while the vehicle rides the crest of a wave or swell. This method requires operator skill to pluck the sub at the proper time and before the next wave or swell reaches the sub. The latter method was selected because it does not rely on any mechanism, which might fail at a most inopportune time, it does not add additional weight to the crane or vessel nor is any additional funding required. The rapid-retrieval method (water to deck) is accomplished in 20 to 25 seconds by use of an aluminum crane and an hydraulic-electro proportional valve system.
To date, two cranes have been fabricated, tested and placed in regular service aboard the two Harbor Branch Foundation research vessels, R/V JOHNSON and R/Y SEA DIVER. A picture of the crane with the JOHNSONSEA- LINK aboard is shown in Fig. 1. The ba1ance of this paper will cover the design fabrication and testing of the crane.