Device for lowering a load, for example a diving bell from a vessel from a spot above the water level to a spot beneath the water level

A device for lowering a load for example a diving bell from a vessel from a spot above the water line to a spot beneath the water line, comprising a winch and a cable connected with the load and moved by said winch along at least one cable pulley rotatable about a shaft. In order to prevent that the cable becomes alternately slack and taut during contact of the load with the water, it is proposed to constantly maintain the taut state of the cable by placing the shaft of the pulley parallel to itself and connecting it with the plunger rod of a plunger cylinder provided with an accumulator.

BACKGROUND OF THE INVENTION 
The invention relates to a device for lowering a load, for example, a 
diving bell from a vessel from a spot above the water line to a spot 
beneath the water line, said device comprising a winch and a cable 
connected with the load and moved by said winch along at least one cable 
pulley rotatable about a shaft. When the load comes into contact with the 
water, the problem occurs that due to heaving of the vessel the cable 
becomes alternately slack and taut. It may, therefore, occur, that when 
the cable is slack the load is solely subjected to the wash of the waves 
and to other movements of the water so that the load may perform 
unpredictable motions. Especially in the case of a diving bell this is 
very troublesome, since the persons therein are exposed to strong, very 
disagreeable movements, for example, when the diving bell tilts. 
Particularly in the case of a rough sea this problem is serious. The 
solution of this problem is rendered difficult, since the force exerted by 
the load on the cable gradually decreases after traversing the water line 
due to the upward pressure exerted on the load by the water. In the case 
of non-solid objects, for example, a diving bell, this change is 
appreciable. When the load is fully immersed, the problem is simplified to 
an extent such that only the heaving of the vessel has to be taken into 
account. 
SUMMARY OF THE INVENTION 
The invention has for its object to provide a solution for the 
abovementioned problems. It tends to provide a device which constantly 
maintains the taut state of the cable both in passing across the water 
line and in full immersion of the load. According to the invention this is 
achieved in that the shaft of the pulley is displaceable parallel to 
itself and is connected with the plunger rod of a plunger cylinder 
provided with an accumulator. When the cable tends to slacken due to 
heaving of the ship, the force exerted by the load on the shaft of the 
pulley is reduced. This results in that the plunger can perform such a 
shift in place that by the simultaneous displacement of the shaft of the 
cable pulley the cable remains stretched. 
An optimum control is obtained by providing two cable discs, the shaft of 
each of which is coupled with the plunger rod of a plunger cylinder, 
whilst the pressure in the accumulator of one of them is chosen so that 
the plunger is in one terminal position when the load is completely above 
the water line and in the other terminal position when the load is fully 
beneath the water line. 
In this way an optimum control can be obtained for the situation in which 
the load is only partly below the water line. When the load has completely 
disappeared below the water line, compensation of heaving is obtained with 
the aid of the second plunger cylinder. To this end the pressure in the 
accumulator of the second plunger cylinder is chosen so that with the 
force exerted on the shaft of the associated cable disc when the load is 
fully immersed the plunger is standing substantially midway between the 
two terminal positions. The plunger cylinders are preferably filled with a 
hydraulic fluid and the accumulators are preferably of a hydro-pneumatic 
type. When the load strikes the water line during lowering, the force 
exerted on the cable will decrease and the plunger will slide out. In the 
event of an upward movement of the vessel due to heaving exceeding the 
downward movement of the load, the force exerted by the load on the cable 
will increase, as a result of which the plunger slides inwards. In order 
to avoid the risk of the plunger striking the bottom of the cylinder with 
heavy force, which would result in a jerk on the cable, the first plunger 
cylinder communicates trhough a conduit with the accumulator, said conduit 
being provided with a valve which blocks the conduit when the plunger 
reaches one terminal position. It is thus ensured that the pressure in the 
cylinder is gradually built up.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
On the ship is installed a winch 2, which drives a cable 3. The cable 3 is 
passed in order of succession around a cable disc 4, a cable disc 5 and a 
cable disc 6. The end of the cable is connected with a load 7. The shafts 
of the cable discs 4 and 5, 8 and 9 respectively are displaceable parallel 
to themselves. The shafts 8 and 9 are coupled with the plunger rods 10 and 
11 respectively forming part of the plunger cylinders 12 and 13 
respectively. Each of the plunger cylinders 12 and 13 is provided with an 
accumulator 14 and 15 respectively. The plunger cylinders may be of the 
hydraulic type and the accumulators of the hydro-pneumatic type. The 
conduit between th accumulator 14 and the associated cylinder 12 includes 
a valve 16. When the plunger reaches the terminal position, the valve 16 
closes in order to brake the movement of the plunger. 
When the water line 17 is attained, the heaving of the ship may cause 
slackening of the cable 3 so that the load 18 gets into a more or less 
floating state and is exposed to the movements of the water. As a result 
the movements of the load will be quite arbitrary. Since the cable 
slackens, the force exerted on the shaft 8 of the cable disc 4 decreases 
so that the plunger 10 is allowed by the force exerted thereon by the 
hydraulic fluid to slide outwards. This movement continues until the cable 
is again stretched so that a state of equilibrium is obtained between the 
force exerted on the plunger and on the shaft 8 by the hydraulic fluid and 
the force exerted on the shaft 8 by the cable. According as the load is 
further immersed, the plunger 10 moves gradually further towards its 
starting position. The pressure in the accumulator 14 is chosen so that, 
when the load 18 is fully immersed, the plunger 10 is in its terminal 
position. Thereafter this plunger does no longer contribute to maintaining 
the cable in the taut state. 
The pressure in the accumulator 15 is chosen so that the plunger 11 has in 
the meantime arrived approximately midway between the terminal positions 
under the action of the force exerted by the cable on the shaft 9 and of 
the force exerted by the hydraulic fluid on the plunger. The compensation 
of the heaving of the ship, when the load 18 is completely beneath the 
water line, is brought about by the plunger cylinder 13. Since with the 
variations of the force exerted on the shaft 9 the plunger 11 will 
oscillate around the central position, it is ensured that the cable 
remains taut.