Dredging with the “Ave Caesar”

Some preparations to the “Ave Caesar” were required before it could be mobilised from Batam. After handling a number of enquiries with various tug owners and marine towage contractors, Lee Trading was contracted to tow the dredger to site.

Leighton-LAMA Joint Venture Section 15: Page 3 of 13 Dredging commenced on 24^th October 2000 after erecting the spuds and releasing all the sea fastenings.

The “Ave Caesar” was a Liebherr 994 Litronic Excavator turret-mounted on a semi-jackup pontoon. The three spuds are not able to lift the pontoon clear of the water but can provide enough lift to hold the pontoon at a stable level unaffected by the short-term water movements. Two of the spuds provide lift and the third provides both lift and longitudinal movement when taking a sliding step. Monthly hire cost is MYR 750 000 based on a single shift.

The “Ave Caesar” is fitted with an electronic Real Time simulator to facilitate accurate dredging work. A Differential Global Positioning System (DGPS), electronic Gyro compass and electronic Tide Gauge were supplied by the J.V. and incorporated with the on-board systems to provide complete three-dimensional control of the dredger and it’s bucket at all times. Initial difficulties were experienced with the integration of the equipment but specialist survey companies were consulted for the final integration of equipment into a workable system. Once operational the system proved very useful for unassisted movement of the dredge and accurate dredging to the requ ired tolerance.

The “Ave Caesar” has a dedicated crew and operators who were familiar with the machine and proved very competent in almost all operations and maintenance activities. A dedicated LLJV Engineer was on board almost full time to manage and witness the operation. Appendix D.4 shows an example of daily dredging records kept and a graphic summary of trench dredging with the “Ave Caesar”. Dredging was a 24 -hour operation with subsequent saving in rental. Refer to Appendix D.5 for typical dredge production figures for both a 12 and 24-hour operation.

One disadvantage the backhoe dredger had over other dredgers is that the jack-up spuds would penetrate up to 10m in the seabed material and the damage would effectively negate or reduce the seabed bearing capacity. This had a little impact on the piled foundation but had far more significance when considering the effect on the originally detailed stone bed design. For this reason attempts were made to keep the dredger’s spuds out of the trench which slightly reduced it’s productivity.

Extra effort was also spent checking that the dredged tolerances were met before the dredger moved off an area. For this reason the bucket was used to systematically sweep the dredged area checking for high spots before making a step.

The trench was excavated according to profiles programmed into the computerized display. Refer Appendix D.6. Excavated material is loaded into a 1000m³ Split-Hopper Barge “Cathay SHB 1006” (At MYR 65 000 per month from Oriental Grandeur plus additional MYR 8 000 for 4 maintenance crew members) moored adjacent to the Dredger. An 800hp tug “Cathay 28” was dedicated to handling of the barge for dumping of spoil and Dredger assistance. Refer to Appendix D.7 for details of the dredging spread.

The excavated material was closely monitored and examined as dredging commenced. Material in the hopper barge is constantly monitored by visual inspection and shear vane test. The excavated seabed was repeatedly inspected by divers to establish the nature of the founding material. The material was soon found to be unsuitable for the stone bed foundation as designed. Material consisted of variable clays, which would liquefy once exposed by excavation (Refer Appendix D.8 for the Trench Seabed Material Survey Record). In the initial dredging stages

Leighton-LAMA Joint Venture Section 15: Page 4 of 13 the machine was moved to various areas on the trench route to produce useable trench in acceptable material.

The foundation conditions were thoroughly examined and an alternative piled foundation was adopted. The relatively small excavator bucket then proved less efficient in the liquefied material. The “Ave Caesar” was off-hired on 15^th March 2001. During this time most of the bulk dredging was completed. A 20m³ clamshell (Jetta 19) was hired to replace the Dipper Dredger since the need for accuracy was reduced. Refer to Appendix D.9 for data on the Clamshell dredger. The large capacity clam proved to be better suited to the conditions and dredging was generally satisfactory. Monthly hire costs ware significantly reduced to MYR 450 000 inclusive of a 1200hp tugboat and 1000m³ hopper barge.

Observations taken between 01/11/00 and 09/02/01 showed that the Ave Caesar backhoe dredger excavated 58% of its total working time and averaged 207m³ per excava ting hour as in the summary below.

Ave Caesar Dredging Production

Activity Unit Nov 00 Dec 00 Jan 01 Feb 01 Total

The average daily production on a double shift could then be estimated as 2 881m³/day (24 hrs x 207m³/hr @ 58% efficiency) but the production rate varies tremendously with material types. Firm material will fill the bucket in a short scoop and will result in as much as 400m³/hr but sloppy mud described as ‘soup’ will yield a very low solid contents value. The total invoiced value of the Macon charter for the “Ave Caesar” running between 20 October 2000 to 13 March 2001 was as follows:

Total Invoiced Value for “Ave Caesar” (MYR)

Prep dredger 34,100

Leighton-LAMA Joint Venture Section 15: Page 5 of 13 This figure does not reflect a number of back charges nor a payment claim that occurred some time later as a result of disputed damage repairs.