COMPLIANT LINEAR TRACTION DRIVE (CLTD)
FOR CABLE & TOWED ARRAY HANDLING SYSTEMS:
The Compliant Linear Traction Drive (CLTD) is a form of "linear traction drive"
or "traction engine", that has been specifically designed and adapted to the
handling, towing and related tension requirements of ship-towed seismic streamer systems.
The CLTD can help reduce the significant manpower requirements often needed to load and
unload large cables from dockside-to-ship.
The CLTD can also be used for ocean bottom
cable laying and other large cable handling requirements. The CLTD is designed to handle a
wide range of streamer sizes and designs. The CLTD "grips" the streamer/array
between two opposing belts and acts to propel or brake as required (see Figures 3 and 4).
The belts are steel-reinforced urethane timing belts, 100 mm wide, that run over aluminum
drive/idler sprockets. The sprockets are supported with sealed, self-aligning ball
bearings, which are further protected from the environment with supplementary Forsheda
V-ring seals. The drive/braking force is supplied by a hydraulic motor through a
serpentine chain arrangement that ensures the belts drive in the same direction and at the
same speed.
The hydraulic system consists of the
motor and a three position, spring-centred, open centre, four way valve. It allows the
operator to drive in either direction, or the open centre allows the CLTD belts to
freewheel in case of an overload condition, or during braking operations. The hydraulic
system uses standard mineral oil-based hydraulic fluids such as Shell Tellus or its
equivalent. The operating speed is controlled manually with the valve; the more it is
opened, the faster the belts travel. The controls are positioned above the frame at an
operator =s height. The gripping or compressive load is applied using pneumatic pressure
from within a "bladder", which in turn exerts force through a series of load
plates to the back side of the belt. The load plates are limited in displacement such that
the grip force is only applied to solid objects in (or on) the streamer such as spacers,
connectors or "bird collars". In this way, the drive/braking load is applied
through the skin directly to the spacers which in turn are bonded to the Kevlar strength
members inside the streamer. In areas where the skin is unsupported, the pneumatic grip
force will flatten the streamer slightly, but will not transmit any significant drive or
braking force to the skin. The pneumatic system consists of a pressure regulator, a
pressure relief valve, a "blow down" valve and two loading bladders.
The bladders are manufactured from high pressure air
hose, which are capped at the ends with rubber plugs. They are then bolted in place to the
CLTD frame. The bladders are contained within a framework which forces the bladders into
an almost flat condition. This then allows the air pressure to be applied in a uniform
manner against the load plates. The single air pressure port into each bladder is located
on the back side of each frame opposite the belt. The required air pressure varies
depending on the task and loads required, but it is generally less than 15 psi. A pressure
relief valve is adjusted to release at about 40 psi. The gripping load from the pneumatic
bladder is transmitted to the streamer spacers through the load plates and the belt. While
running, the belt slides over the stationary load plates. The load plates are linked
together and held in position using rivets, to a length of fabric- reinforced rubber
belting, which in turn is fastened to the end of the frame assembly using the same bolts
as the bladder. The cross section of the load plates is curved in order to direct the
streamer into the centre of the belt. To ensure correct performance, however, the streamer
must also be directed straight down the centreline of the belt at the entry/exit
locations, using a sheave accessory package.
