Requirement_on_Heave_compensator_DC.docx

Purchase Requirement

OPPORTUNITY TITLE: Ship heave compensation system to stabilize payload tethered off rear of a ship in a seaway

(Short title: Ship heave compensation system)

The US Naval Research Laboratory requires a ship heave compensation system to allow a tethered/suspended underwater payload deployed off the rear of a research vessel/workboat to remain in a fixed position relative to the ocean bottom. Both active or passive compensation systems will be considered. The minimum requirements are the following

1) The seaway has a characteristic wave amplitude of approximately 1 m and assumed frequency of 0.1 Hz. (2 m crest-to-trough vertical distance).

2) With motion compensation in use, the submerged payload’s vertical motion is reduced within 20% of the heave amplitude of a point on the rear of the ship when heading into a seaway (case of maximum ship pitching).

3) The ship is drifting during operations, but nominally steered into the seaway.

4) The peak vertical speed at a rear-most point on the ship is 0.9 m/s (this is the minimum combined heave and pitch motion that must be compensated).

5) The submerged payload creates a line tension of approximately 1700 N.

6) The system must be mountable on the deck of the ship (ideally with standard bolt hole pattern).

7) If the moving compensation mechanism is located on the deck of the ship, the mechanism should not radiate in excess of 90 dB acoustic noise level in air referenced to 1 m from mechanism.

8) Compensation solutions featuring moving underwater components may be possible provided vendor can provide an underwater indication of noise level (dB) referenced to 1 m from mechanism.