D-4 



PBM 



Function : Pipe trenching. Pipe diameters - 15 to 122cin (6 to kQ in.). 



Trench depth - 2in (7 ft), k.'^m (l5 ft) can "be reached by making several 



passes over the trench. 



Operating Depth : 650in (2,132 ft) (Equipment can operate to depths equal 



to the power of normal air compressors to supply air, depths of 60 to 



65m (197 - 213 ft) are easily obtainable.) 



Dimensions (LxWxH) : 6m x 1.8m x 3.5m (20 ft x 5-9 ft x 11. 5 ft) 



Weight (Dry) : lOt (ll tons), can be made neutrally buoyant in water if 



required. 



Speed: 50m (16U ft)/hr in sand. Work terminates in current speeds 



exceeding 1.6 knots (2.9 km/hr). 



Power : Air compressors delivering 30,000 Itrs/min at 7 to 9kg/sq cm 



(100 to 128 psi) are satisfactory. 



Propulsion : The machine moves along the pipe by means of a push-pull system 



which operates hydraulic clamps with internal rubber protection. The 



machine is locked around the pipe (by divers) and operates at neutral 



buoynacy to avoid applying great stresses to the pipe. 



Tools/instrumentation : A water jet cuts the sediment in front of the 



machine, cuttings are removed by air lift (shallow water) or by water 



pumps (deep water). 



Navigation : Initial positioning and clamping to the pipe is directed 



by divers. 



Shipboard Components : Control cabin, hydraulic power pack, high pressure 



water pumps, air compressors, umbilical winch and cable, electric power 



generator, handling system, workshop van. 



Support Ship Requirements : For shallow water (less than 50ni depth) in 



good weather: a small supply vessel equipped with a 20 ton A-frame, 



an eight-point mooring system, deck space adequate to contain the above 



equipment, shallow diving equipment and accommodations for 12 people. 



Deep water: larger craft with 50 ton A-frame, one deep-diving unit and 



accommodations for 25 people. 



Status : Several PBMs (of different sizes and capabilities) are operational 

 Builder/Operator : Sub Sea Oil Services S.p.A. 



Milan, Italy 



