4d fixed installation seismic 31
Seismic lead-in termination for wide tow/high loads
T
oday’s 3d seismic operators tow the low profile helical
16 plus streamers to provide rod system provides
staggering amounts of data to meet bend protection with
client demands. this has led the less drag, can be easily
industry to push for a low profile full wound on a cable
strength seismic lead termination drum, and as such is
that can grip a faired lead-in as well well received by seismic
as provide lead-in bend protection. operators towing
in addition the termination must multiple streamers.
be able to be installed mid span at additional features
any location on the lead-in and be which make the dHss
conveniently designed so it can be versatile for towing
wound on a cable drum. seismic lead-ins are its
Pmi industries inc has met this two degrees of freedom with respect includes shackles and rope sheave
challenge with the dyna-Hanger to the cable axis. the dHss helical inserts. dHss hardware is supplied
suspension system (dHss), a highly rod layers are captured in a split in kit form for customer shipboard
reliable cable attachment point housing which is bolted together installation. no special tooling
for seismic streamers, paravanes, and fixed on the cable. the housing is required to install a dHss. Re-
surface and subsurface floats, cable has a circumferential groove which termination kits for all dHss systems
depressors and where ever a mid span accepts a collar assembly which can are available. a re-termination kit
termination is required. rotate 360 degrees around the cable. includes replacement dHss helical
dHss lead-in gripping and bend attached to the collar assembly are rods as the major stainless steel
protection is accomplished with a pair of trunnion mounted arms machined parts are re-useable.
multiple layers of helically preformed which articulate fore and aft, the typically the working life of dHss
high strength electro-galvanised arms connect to the spread ropes. rods, under constant towing
steel rods. the helical gripping these two degrees of freedom allow conditions, is 12 to 16 months.
concept is not new, it has evolved the lead-in to rotate and the arms to the dyna-Hanger suspension
over 40 years and its use for holding align with the load. for deck storage system is an engineered system; Pmi
underwater cables has been proven the collar assembly with arms can be has designs for the most widely used
by years of field use. What’s new quickly removed allowing the housing seismic lead-ins and develop new
is the use of multiple rod layers, and rods to be reeled directly on the designs and attachment points as
of staggered lengths, to provide cable drum. the seismic industry advances lead-in
varying stiffness for seismic lead- the dHss has been designed technology. l
in bend protection. lead-in bend for a variety of cable sizes, and the
enter 31 or ✔ at www.engineerlive.com/ihss
protection was formerly provided by attachment to the arms has been
much larger profile (higher drag) all designed to meet customer towing PMI Industries, Inc is based in Cleveland,
polyurethane bending strain reliefs. and interface requirements which Ohio, USA. www.pmiind.com
Seismology boat targets shallow marine transition zone
W
ith the launching of the explorer 5, dmt GmbH between deep water and the shoreline. Here an air pulse
has put an additional shallow marine seismic unit, the ‘air gun’, generates acoustic waves that are then
vessel into service. this provider of technical services, reflected from the earth’s strata. these acoustic reflections
headquartered in essen, Germany, will use the boat are picked up and measured with hydrophones connected
for seismic measurements in the transition zone, the to special cable networks. the time that passes before the
boundary area between deep sea and onshore seismic sound returns and reaches the hydrophones gives dmt
operations. engineers insights into the geology of the subsurface
“the boat can be readied for use in no time at all strata. the system assists in detecting, exploring and
and can be conveniently transported inside a standard developing previously unknown deposits of natural
shipping container,” explained dmt department manager resources.
Rene Pool during christening ceremonies for this vessel in the explorer 5 can, on the one hand, be used to lay the
the netherlands. hydrophone cables. it can also transport the air gun, an
the explorer 5 will be employed primarily in shallow environment-friendly sound source. l
waters – in lakes and especially near coastlines in order
to make seismic measurements in the ‘transition zone’ For more information, visit www.dmt.eu
www.engineerlive.com
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