The ENSCO Sextuplets

Wednesday, September 18, 2002
There are no doubt scores of 15 to 20-year-old 180-ft. supply boats that still have years of useful life… if renovated by skillful and creative marine engineers. That is what ENSCO Marine Company, Broussard, La. has done with a six-pack of vintage supply boats whose day rates and utilization had slipped due to age and limited carrying capacity for their size.

ENSCO Marine is a division of ENSCO International, a Dallas, Texas-based drilling contractor who owns and operates 56 drilling rigs in the Gulf of Mexico, the North Sea, Asia Pacific and South America. ENSCO Marine operates 23 offshore supply boats and five anchor handling tugs. "A few of our boats are contracted as packages with a rig, but that is the exception rather than the rule, said Bill Landen, manager of business development for ENSCO Marine. "Most of our vessels are contracted to the major oil companies just as our rig division contracts their drilling rigs," Landen said.

Six of ENSCO's offshore vessels were practically identical 181 x 40 x 14-ft. supply boats. Built by Moss Point Marine, Escatawpa, Miss., in 1983, these vessels were first line supply boats for their time and ENSCO Marine thought they could extend their life with an aggressive modernization program. . "With identical vessels, we only had to do the engineering once and develop one set of plans," Landen added. Schuller & Allan of Houston did the engineering along with ENSCO's engineers.

"The key to our upgrading program was to significantly increase their liquid mud carrying capacity, " said Steve Bellingham, manager of engineering for ENSCO Marine. The six vessels could only hold 1,568 barrels of liquid mud and ENSCO wanted to more than double it to be competitive with similar sized supply boats Early on in the engineering design phase it became obvious that the vessels would have to be stretched via a mid-body plug to get the increased mud hauling capacity. A 50-ft. mid body section containing four mud tanks was inserted just aft of the bulk mud tanks and immediately forward of the existing mud tanks. Now with eight mud tanks the vessels have the ability to carry 3,760 barrels of liquid mud.

Not only was tank capacity increased, the pumping and piping circuits were reworked to give ENSCO the option of carrying and delivering two types of mud without contamination on delivery. Stirrers were built into the new mud tanks and retrofitted on the existing four mud tanks. Changes were also made in the bulk mud systems located just forward of the liquid mud tanks. The four existing 1,000 cu. ft. tanks were removed and replaced with four 1,500 cu. ft. tanks and the compressed air delivery system was upgraded to 80 PSIG. New compressors and their electric motors were also replaced with larger capacity models.

Transferable fuel was greatly increased from 46,000 gallons to 94,000 gallons. Drill water carrying capacity was decreased from 90,000 gallons to 66,664 gallons because one tank was eliminated due to space restrictions when installing a new propulsion system. "However if we have basically a "water job" we can use our mud tanks to haul water, so with our increased mud capacity, we can actually haul more water in these boats than before," Bellingham said.

Above the hull is a new and larger 168-ft. by 29-ft. cargo area capable of holding up to 800 long tons. The vessels were also repowered. Three of the vessels had a pair of Detroit Diesel 16V149 engines each developing 900 hp. The other three vessels each had two Caterpillar 3512 engines that were rated at 1,200 hp each.

All six vessels were repowered using Caterpillar 3512 B engines rated at 1,500 hp each. The engines power a pair of Ulstein azimuthing Z-drives with 360 degree rotation. An Ulstein 650 hp bowthruster replaced the smaller 300 hp bowthruster originally installed. The exhaust stacks and trunk were relocated from the "Gulf of Mexico" location on the bulwarks aft to the "North Sea" style location just behind the pilothouse. The power for the bowthrusters on the six vessels comes from the six Caterpillar 3512 engines originally installed on three of the vessels as main propulsion. The engines were overhauled and a new 850 kW generator added to power the AC motor that drives the bow thruster.

The two Detroit Diesel 99 kW generators used for ship's power were rebuilt and reinstalled on the vessel. The Detroit Diesel 8V71 prime movers for these generators also drive the liquid mud pumps through a PTO and speed increaser. A new ship's service switchboard with parallel capability was installed SOLAS required the addition of an emergency generator

The large Caterpillar 3512 genset used to power the bowthruster also provides power for the new rotary dry bulk compressors. The pilothouse also received a complete makeover. "Essentially it was gutted," explained Bellingham. "We had to make room for significantly more electronics gear so we lengthened the pilothouse by three feet and then rebuilt it," Bellingham added. Other navigation gear onboard the six supply boats include two radars, an autopilot, GPS, a fathometer and a gyroscope.

Among the more significant pieces of electronic gear added was a Konsberg-Simrad dynamic positioning system as well as the pair of controllers for the Z-drive system and the new bow thruster. "Station-holding capability with our new DP system and the maneuverability offered by our Z-drives makes these vessels extremely 'rig friendly'," said Landen. A complete GMDSS communications suite was installed for area A3, which typically includes two VHFs, a MF/HF unit and an Inmarsat satellite communications system. The alarm panel was enlarged to handle the many more points that needed to be monitored on this more technologically advanced vessel.

A complete SOLAS review of the vessel was undertaken resulting in upgrades to the safety and firefighting systems and also to the galley and accommodations. As before, the vessels can carry 17 people in seven staterooms. The first boat renovated in the series was the ENSCO Pilot in 1998 by Newpark Shipbuilding in Houston. It was a little different from the five vessels that followed in that it had a 40-ft., rather than 50-ft. mid body installed. Following behind the ENSCO Pilot and returned to service has been the ENSCO Admiral, ENSCO President and ENSCO Commander. The ENSCO Navigator is the last in the series and is expected to be delivered by the end of the year. All five of these vessels have been renovated at Eastern Shipbuilding, Panama City, Fla. The renovation of these vessels has done wonders for their marketability and utilization. Before the work, these vessels in the fleet averaged a utilization of under 80% … now it is typically 95%.

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