Support Vessel Requirements
To give the user an idea of the general support vessel requirements, the following are specifications for a Jason/Medea support vessel. These requirements are intended as guidelines for the selection of a ship suitable for offshore operations. Modifications/reductions to these specifications are possible when using the DSL-120A towed system.
Non-UNOLS vessel use should be approved by DSG and will probably require additional funding.
ISO Shipping Containers
Four 20’ x 8’ x 8’ ISO shipping containers (vans) fitted out as control rooms and workshops. Each container weighs approximately 15,000 pounds. One 8’ x 12’ x 7’ van weighs 6,000 pounds. Each container must be welded (or bolted) and chained to the deck (total area required is 740 ft.2).
Deep Sea Survey Winch
This assembly is comprised of the following components:
| Weight | Size | |
|---|---|---|
| Traction Unit | 22,050 pounds | 12’L x 7’3”W x 12’H |
| Level Wind | 2,900 pounds | 7’9”L x 4’3”W x 6’H |
| Storage Drum | 30,800 pounds | 7’9”L x 7’3”W x 6’8”H |
| Diesel Power Pack | 7,500 pounds | 11’L x 4’W x 7’H |
The winch is normally mounted on the centerline near the stern of the vessel.
HIAB 180 Sea Crane
This component is used to deploy and retrieve the ROV or towed system and thus must be placed on the deck near the overboarding point of the main tow cable. Note that the ship’s deck must be sufficiently strong to withstand the loads resulting from operation of this piece of equipment. A working area for the ROV serviced with this crane must be provided; deck space of 150 ft.2 will be adequate.
| Weight | Size | |
|---|---|---|
| Crane | 7,400 pounds | 12’L x 7’3”W x 12’H (folded) working radius @4,500 lbs: 27’ |
| Power Pack | 650 pounds | 3’6”L x 2’W x 3’H |
Tow Cable
To support the subsea system, the ship must be capable of handling a tow cable over the side. This cable is an electro optical design with steel reinforcing armor. Typical overboarding of this wire is done from a sheave mounted to either an A-frame or suitable crane. Tow point locations at the stern (on centerline) or amidships over the side have been used. A tow point must be at least 10 feet outboard and 10 feet above the deck plane. Tow points must also be capable of supporting a maximum wire load of at least 50,000 pounds. Additionally, mounting points should allow deployment and recovery of the wire from its outboard location to a point no less than 5 feet inboard. Should the candidate vessel not have sufficient overboarding capacity, an A-frame will be installed as part of the system. As with the HIAB crane, the ship’s deck must have adequate strength to support this installation.
| Weight | Size | |
|---|---|---|
| A-frame | 10,800 pounds | 15’L x 12’W x 17’H 9’9” overboard reach |
Power Requirements
Power requirements for the system are as follows (60 Hertz):
| Voltage | Amperage | |
|---|---|---|
| Control Van #1 | 440 30 | 50 |
| Control Van #2 | 440 30 | 50 |
| Rigging Van | 440 10 | 20 |
| Tool Van | 440 10 | 20 |
| Winch Van | N/A | |
| Survey Winch (if diesel is not used) |
440 30 | 700 start (200 max. running) |
| HIAB Power Pack | 440 30 | 50 |
Note that if the survey winch is powered by its diesel, no electrical power from the ship is needed. In this case however, diesel fuel from the ship will be required. Power pack must be filled once each day the system is operated, and tank capacity is approximately 55 gallons.
Station Keeping
To accomplish precise surveys with the ROV system it is necessary that the support vessel be capable of station keeping while at sea. Ships that have been used previously have all been equipped with dynamic positioning (DP) systems capable of receiving positioning input from external sources. These inputs are normally provided from systems such as GPS or long baseline underwater acoustic sources. These sources are part of the Jason/Medea system and have been tailored as inputs to a specific support vessel’s DP controller. Station keeping within a watch circle not exceeding 80 feet is required.