Hydraulic and earth engineering – Marine structure or fabrication thereof – With anchoring of structure to marine floor
Patent
1995-07-03
1998-08-04
Taylor, Dennis L.
Hydraulic and earth engineering
Marine structure or fabrication thereof
With anchoring of structure to marine floor
405232, E02D 710
Patent
active
057884188
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention deals with a detachable connector for the transmission of drive energy to submersible pile drivers and cut-off equipment or similar equipment from above the water surface to the submerged work units.
For underwater pile driving on the sea floor, the pressure medium required for driving the equipment is supplied through a pressure medium circuit with long hoses from above the water surface to the work unit. Because of the flow resistance in the hoses, this is only feasible up to a certain water depth. Either the hose diameter must be increased or several hoses must be utilized next to each other, so that the flow resistance can be kept low and the pressure medium pumps can still cope with the additional pressure required to overcome it. Finally, the limits of feasibility, economy and also handling are reached.
In that case, a submersible drive unit is connected with the equipment and lowered together with it, supplying pressure medium through a short closed circuit, while, for the operation of the drive unit, electric energy is supplied by means of a long electric power cable from above the water surface with now much lower resistance, i. e. energy losses. For the operation of this kind of work unit/drive unit combination, at least one line for the supply of compressed air to the work unit is usually required in order to compensate for the outer pressure on enclosed empty spaces, and control lines for the control and monitoring of the work unit are also needed.
All these lines are gathered in one conduit only, the umbilical, so that only one line need be handled.
The umbilical is heavily reinforced for protection of the internal lines and for loading with tensile forces. It makes the greatest demands on manufacturing and can cost up to US $1400.00 per meter. It is substantially more expensive than a lightweight umbilical, as used for the operation with long hoses described in the beginning, which contains only control lines but no electric power cables. Depending on the equipment size, the energy to be transmitted and the operating depth, a long umbilical with accessories can therefore be more expensive than the pile driver itself. Price and fear of damage discourage its use.
Therefore, again and again, solutions have been tried using even longer and an even greater number of parallel hoses and lighter umbilicals; although these solutions appeared cheaper, failures have been more frequent because of high risk handling and ensuing higher costs. This is because the cost of one hour of downtime of a support ship can be as high as US $17,000.00, not counting the water pollution caused by the hose failure.
The costs for the heavy umbilical with winch, as well as for the pile driver/drive unit combination are driven even higher, because, in anticipation of failure of lines in the umbilical and/or one or more motor-pump units, the umbilical is equipped with a greater number of electric power cables and signal lines, or the drive unit is equipped with a greater number of, or larger, motor-pump units than required, since a quick remedy is currently not possible in the eventuality of a failure.
Moreover, the working speed of the equipment is based on standards which are common to conventional pile driving above water, which drives up the capacity of the work unit unnecessarily causing additional costs which are not commensurate with the derived benefit for underwater work.
The present situation of incurred downtime and damage costs of several million dollars has been tolerated for years. This is technically and economically unsatisfactory and this is also unsatisfactory because the expensive underwater equipment is needed only infrequently and only for short periods of time, i. e. it cannot be amortized quickly enough. However, the operation with long hoses in the appropriate applications is also still unsatisfactory and in need of improvement.
Similar problems occur with other work units, especially with underwater cut-off equipment which will be utilized more and more in
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