U.S. NAVY SALVAGE REPORT DEEPWATER HORIZON ... - ESSM

At the conclusion of the brainstorming session, Captain Keenan (SUPSALV)
directed the execution of a quick field test, with an existing vessel, of the effects of
crabbing on skimming operations. LT Shaun Hayes and Mr. Bob Urban, PCCI,
Inc., conducted a test with an available 205-ft OSV and NOFI CurrentBuster.
Figure 3 is from the quick sea trial conducted which showed some initial promise.
Limitations:
Identified limitations to the proposed solution include:
1. Effective encounter width is limited by 1) the length of the vessel and 2) the
angle of “crab”
o A typical OSV might be 190 to 250 feet long; at a 20-degree “crab” this
equates to a possible increased in encounter width of 65 to 86 feet
o A typical towed barge might be 300 to 400 feet long; at a 20-degree “crab”
this equates to a possible increase in encounter width of 103 to 137 feet
o OSV with CurrentBuster field test identified 12-degree “crab” as optimal
given the environmental conditions at the time
o A towed barge system would be limited by the towing vessel’s capability
and hull and wave resistance of the barge
2. The skimming speed achievable by the system employed
o It is anticipated that an OSV could skim at 3 knots and transit at 10-15 knots
with skimming system recovered
o It is anticipated that a barge could be towed at 3-4 knots while skimming at
an angle and towed at 5-7 knots while in transit
3. Relative speed and direction of wind compared to oil skimming
o Wind may limit OSV “crabbing” angle due to thruster power limitations
o Wind may decrease or increase effective “crabbing” angle of a towed-barge
o Wind effects on the skimming system may limit “crabbing” angle
4. Sea-state for transit and for skimming
o Sea-state for transit is limited by vessels involved and towing configuration
as applicable
o Sea-state for skimming is limited by the size of the barrier and the rigging of
the employed pump/skimmer
Recommendations:
1. Spill operations should plan for single skimmer operations as oil spill matures.
2. When conducting single skimmer operations, the vessels must have the
capability of maintaining the “crabbing” angle while skimming and handling
collected debris and skimmed oil
3. In anticipation of higher sea state operations, the use of larger OSVs or the
development of a towed-barge system is necessary. For a towed-barge system,
SUPSALV and NAVSEA can provide personnel to assist with this evaluation to
include:
D-4