Subtrench 2 Trencher

System Technical Assessment

Prepared by:- W.P.Croager – EDC Limited

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 CONTENTS
1 INTRODUCTION .......................................................................................................... 3
2 VEHICLE FRAME AND STRUCTURE ..................................................................... 4
2.1 RECOMMEDATIONS .......................................................................................... 4
3 TRACK DRIVE SYSTEM............................................................................................. 5
3.1 TECHNICAL ASSESSMENT .............................................................................. 5
3.1.1 DESIGN LOAD AND LIFE.......................................................................... 7
3.1.2 SEALS AND SEAL COUNTER-FACES.................................................... 7
3.1.3 PRESSURE COMPENSATION ................................................................... 8
3.1.4 DRIVE MOTOR PRESSURE & FLOWS ................................................... 8
4 HYDRAULIC SYSTEM................................................................................................ 9
4.1 GENERAL DESCRIPTION .................................................................................. 9
4.2 TECHNICAL ASSESSMENT ............................................................................ 10
4.2.1 HPU PUMPING SYSTEMS ....................................................................... 10
4.2.2 TRACK DRIVE CONTROL SYSTEM ..................................................... 11
4.2.3 CUTTER DRIVE CONTROL SYSTEM ................................................... 11
4.2.4 AUXILLIARY SYSTEM ............................................................................ 11
4.3 COMPENSATION & SYSTEM INSTALLATION.......................................... 15
4.3.1 TECHNICAL ASSESSMENT .................................................................... 16
4.4 HPU MOTOR & COOLING ISSUES ................................................................ 17
5 WATER SYSTEM........................................................................................................ 19
6 BURIAL SYSTEMS..................................................................................................... 21
7 SURFACE ELECTRICS .............................................................................................. 24
7 SURFACE ELECTRICS .............................................................................................. 24
8 UMBILICAL & WINCH ............................................................................................. 25
9 SUBSEA ELECTRONICS AND ELECTRICS ......................................................... 26
10 SURFACE ELECTRONICS AND SOFTWARE .................................................. 27
11 SUMMARY .............................................................................................................. 28

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1 INTRODUCTION
This report is the result of a request by Oceanteam Power and Umbilical (OPU) to
perform a preliminary assessment of the Subtrench Two (ST2) trenching system.

As was highlighted in the report of the Van Oord equipment the ST2 is not a finished
article and should only be considered to be in a prototype stage of development.

It is the purpose of this report to highlight some of the areas that require development and
redesign to provide a reliable, operational and maintainable tractor/trenching unit.

It is understood that the system was intended for operation from depth of 100 metres to
the tide line. It is not currently a system that can operate at any distance from a water
supply that is not adequate to cool the prime mover electric motors. (Pleuger, the motor
manufacturers, quote water supply requirements of 100m3/hr for each electric motor).
The onshore logistic requirements to satisfy this need are not insignificant. The only time
that ST2 has been used for a beach transition the cooling water was supplied from an
offshore barge.

At present there is a not a clear understanding of the current status, capability or

functionality of the system.

To summarize the current operational parameters:-

Maximum Operational Depth - 100m seawater.

Minimum Operational Depth - 0m
(Providing there is an adequate water supply).
Minimum Track Ground pressure - 37kPa to 25kPa Pa in air.
- 32kPa to 20kPa in water.
Deployment and operation - Diver Assistance required.
Operation & Maintenance - Input from Subtrench Pty Personnel
required.

It is the purpose of this report to identify the major areas where additional work is
required. It should not be considered a final and exhaustive definition because as work is
started it is not unrealistic to expect other areas will be found that require attention.

This report reviews each major component or system which requires attention, provides a
summary description, identify the status and make recommendations.

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2 VEHICLE FRAME AND STRUCTURE
The vehicle frame appears to be a simple and robust structure which provides the base for
mounting the Komatsu PC300-3 track frames and tooling. There is a Finite Elemant
Analysis (FEA) of the frame produced by Worley Parsons Services Pty. Ltd, Australia.

It appears to have been conducted using the DNV Dynamic Amplification Factors (DAF)
and load cases supplied by Subtrench Pty.

Whether the load cases applied and the DAF used are appropriate to the current vehicle
configuration and intended use would have to the subject to a more detailed investigation.
It is quite apparent that the vehicle current status does not reflect the original design
intent. As an example the original concept for the vehicle included:-

1. An articulated boom crane for loading cables onto the vehicle for post lay burial.
2. A docking system for launch and recovery.
There may be many more elements of the design intention which may have been ‘lost’ or
changed due to the pressures of project timescales.

The impression is that the engineering approach initially used was measured and
professional and that subsequent project timescale pressures compromised the design
intent. It is clear that a number of modifications were made at a very late stage which
were expedient ‘quick fixes’ which has compromised the integrity of the design intent
and the quality of the work is in some case poor. The overall maintainability and
accessibility of the vehicle is very poor and will be discussed in more detail later in the
report.

It should be noted that the tubular structure of the frame has been designed as a pressure
vessel. This has been done to reduce in water mass and to prevent internal corrosion.
After lift testing in Zuillichem a certification plate has been attached to the tubular frame
by drilling and pop-rivets! This will require inspection and rectification.

The attachment for the umbilical the vehicle is starboard mid-ships and is rigidly bolted
to the vehicle structure.

2.1 RECOMMEDATIONS
Once a clear definition of the system specification has been decided and a viable
engineering solution has been identified the FEA study will need to be reviewed and the
applicability verified or a new study conducted.

The attachment and location of the umbilical termination will require reviewing once the
functionality required has been determined.

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3 TRACK DRIVE SYSTEM
It is understood that the track drive system utilises standard Komatsu PC300-3 left and
right hand track groups. This comprises the left and right hand track frames, front idlers,
carrier rollers, track rollers and motor/gearbox/sprocket drive assembly. The standard
track chains are used but custom designed track-plates or grousers are utilised. The
custom grousers are manufactured from an abrasion resistant plastic and have overall
length of 1.6 metres.
(N.B. From discussions with John Hall of Kamatsu at Redditch who kindly supplied
copies of service documents the, PC300-3 is quite an old mark of track assembly, the
current production mark is eight. He doubted that there were significant changes between
the Mk. 3 and Mk. 8 and remanufactured spares should be available.) Subsequent
investigation has revealed that the components do not correlate with the Komatsu
manuals. We need to establish the correct mark and model of the track assembly
components.

3.1 TECHNICAL ASSESSMENT

Komatsu have an excellent reputation for designing and manufacturing tracked vehicles.
With regard to the chains and where the chains interface with the idlers, sprockets, carrier
rollers and track rollers operation in a sub-sea environment should provide few issues.
The environment is probably no better or worse than the normal working environment for
this type of equipments but operating with a salt water environment should be verified.
The only issues which could compromise the integrity of the track drive system are
associated with whether:-
A. It is operating within the design load capability to provide an acceptable operating
life.
B. The seals and seal counter-faces are suitable for the environment.
C. Sealed bearings and gearboxes are adequately pressure compensated.
D. The pressures and flows applied to the standard drive motor are within the normal
operating range.
It had been noted by Van Oord that during the last phases of the systems operation on the
Q7 project it had been difficult to maintain heading. On subsequent recovery of the
system from the barge to the yard at Zuillichem the left hand track had made ‘unusual
noises’ and was difficult to steer indicating problems with the associated gearbox.
From discussions with Julian Brede of Subtrech Pty it was found that gearbox had been
‘packed with grease’ to provide lubrication but no effort had been made to pressure
compensate the assembly.
This is well recognised as an inadequate method for providing pressure compensation and
lubrication unless the seals of the hydraulic motor and the gearbox are capable of
withstanding the full operating depth pressure of the vehicle, which they are not.
The ‘noisy’ left hand gearbox was removed from the vehicle at the Oceanteam base in
Dundee and it was found that the static casing of the gearbox had burst and ball bearings
from a ball race dropped out!
This may have been caused by the lack of pressure compensation but as it was noted that
the track frame is ‘scalloped’ away around the mounting for the track drive gearbox. It is
possible that ‘hard’ matter, such as flint coble, may have been carried around by the track

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chain and trapped into this cut away. To determine the exact cause of failure further
investigations and discussions with Komatsu are required.

View of Damage to Port Track Drive Gearbox

‘Scallop’ of Port Track Frame Gearbox Mounting

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Starboard Track Drive monted to track frame showing ‘Scallop’

3.1.1 DESIGN LOAD AND LIFE

There are two routes to verify efficacy of the standard track assembly; revert to Subtrench
Pty or independently review the system by obtaining the operating specification from
Komatsu. As Subtrench Pty retains intellectual property rights to the design I suspect that
they may not be forthcoming.

Recommendations
Liaise with Komatsu and verify that the track assemblies are operating within the
allowable Gross Vehicle Weight limits.

3.1.2 SEALS AND SEAL COUNTER-FACES

With regard to the sealing and seal counter-faces the environment is probably no better or
worse than the normal working environment for this type of equipments but operating
with a salt water environment should be verified. (The author has some experience with
use of the type of seal used by Komatsu and provided that the correct seal type is
specified and it is pressure compensated then they are fit for purpose.

Recommendations
Liaise with Komatsu and verify the that the sealing arrangement is compatible with the
operating environment.

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3.1.3 PRESSURE COMPENSATION
This has proved to have caused a major failure of one of the gearbox of the track drive
system.
The right hand track drive motor was then removed and stripped in an effort to determine
the cause of failure. The motor was found to be full of emulsified/solidified grease and
water. One of the bearings was seized and the second could only be rotated with great
difficulty. The ‘O’ ring energising the seal was broken and deposits of sand were also
noted in the seal bearing area.
It was also noted that there did not seem to be any other steps taken to seal other static
joints in the gearbox housing or the various fill and drain points on the gearbox housing.
The conclusion is clear that the gearbox is inadequately pressure compensated.
It is suspected that the carriers and idler bearings will also be damaged to a greater or
lesser extent by water ingress due to inadequate pressure compensation. It is
recommended that all carriers and idlers should be stripped for inspection and assessment
of the most efficacious method to provide adequate lubrication and pressure
compensation.
The Komatsu hydraulic drive motor seal and shaft should also be inspected for damage as
it is suspected that the seal may have blown and this could result in damage to the shaft.

It should be possible to modify the standard Komatsu components to enable good

pressure compensation and lubrication to be achieved but this will require further
investigation and design.

Recommendations
Liaise with Komatsu to enable an engineered design to be implemented to properly
pressure compensate all elements of the track drive system, gearboxes, idler bearings and
carriers.

3.1.4 DRIVE MOTOR PRESSURE & FLOWS

It should be verified that the drive pressures and flows that can be applied to the track
drive motor are within limits acceptable to Komatsu. As an operating pressure of 350bar
has been fairly standard in the mobile hydraulics market for a number of years it is
unlikely that the operating pressure will be an issue. It is noted that the hydraulic
schematic indicates that a brake is fitted to the motor this should be verified as there is
the potential for uncompensated and unvented voids to exist.

Recommendations
Liaise with Komatsu and verify system limitations any potential compensation and
venting issues.

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4 HYDRAULIC SYSTEM
The ST2 hydraulic system is a relatively simple. The as built system was found to be at
variance with original documentation delivered with the system.

After contacting Julian Brede of Subtrench Pty. Ltd in Australian more current
documentation was sent as part of the O&M manual which was more consistent with the
as built system but there were still inconsistencies. In addition there were a number of
elements which it has not been possible to verify because of the poor accessibility
described in later sections of this report. Whilst additional time could have been spent
investigating these areas the author considered that it was beyond the terms of reference
for this investigation.

Recommendation
The system should progressively dismantled and the information gathered used to
construct an accurate hydraulic schematic. This will enable a complete review to be
conducted of the efficacy of the system design.

4.1 GENERAL DESCRIPTION

The prime movers consist of two identical 180kW electric motors each driving three
close coupled hydraulic pumps. The pump sets are also identical and consist of two close
coupled closed circuit variable displacement hydraulic pumps of 125cc/rev capacity and
56cc/rev. The third pump is an open loop variable displacement constant pressure pump
of 28cc/rev.

The larger closed circuit pump of both motor/pump sets each supply one of the trenching
cutter motors, the smaller capacity closed loop pump each supply one of the track drive
motors and the third pump is used to provide supplies to the auxiliary functions such as
actuators for tooling control.

Two proportional pressure control valves are used to control the direction of and the
magnitude of fluid flow to and from each of the closed loop pumps. As the trench cutter
drive and the track drive motors are all of the fixed displacement type this provides
control of the speed and direction of rotation of the cutters and track drives.

The proportional pressure control valves are supplied from the boost circuit of the larger
closed loop pump.

The main hydraulic system is pressure compensated by six spring biased compensators
with an estimated theoretical capacity of 12.5 litres. The compensators have been marked
with a fill limit approximately equivalent to 8 litres of useable capacity. The
compensation pressure is estimated to be approximately 1psi when the compensator is
full.

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There are four electro-hydraulic valve packs fitted to the vehicle. One is dedicated to the
proportional pressure valves used to control the displacement of the closed loop pumps.
The three other valve packs contain directional control valves for operation of the
auxiliary functions.

There are also two sets of diver operated directional control valves which duplicate some
of the auxiliary functions. There is also the facility to power the diver operated valves
from a hot stab hydraulic supply.

4.2 TECHNICAL ASSESSMENT

The hydraulic system was designed by and the major components, such as pumps and
valves are manufactured by, Bosch Rexroth. Whilst this is a reputable manufacturer of
high quality equipment it is unusual for them to have any experience in the design of sub-
sea vehicle systems or how to adapt surface hydraulic equipment for sub sea use.

Typical examples of this are:-

1. Inadequate pressure compensation of assemblies and components.

2. Selection of inappropriate seals and counter-face materials.
3. Incorrect sizing of hoses and pipe work systems.
4. A complete lack of understanding of the requirements and function of a hydraulic
compensator.
5. Poor comprehension of the importance of being able to vent and bleed all the air
out of pressure compensated assemblies.
6. Heat dissipation.
A sample of the hydraulic fluid has been taken from the system and was found to be in
good condition with a cleanliness probably better than NAS Class 6.

4.2.1 HPU PUMPING SYSTEMS

The concept of using multiple pumps close coupled and driven by a single prime mover
is a simple and proven method of providing independently variable pressure and flow
sources from the same drive motor. The only issue would be whether sufficient
consideration has been given to ensuring that potential voids between the close coupled
pumps are adequately vented and pressure compensated.
Inadequate pressure compensation could result in water ingress to the hydraulic system.
Inadequate venting will result in high demands being placed upon the capacity of the
pressure compensation system.
Currently the HPU pumps and motors are enclosed in an open ‘bath tub’ to allow the
motor to be submerged in water for onshore operations. This has made accessibility for
maintenance and servicing virtually impossible. There are also other important
considerations which will be discussed in a subsequent section of this report.

Recommendations
Discuss, resolve and design an engineering solution to any potential problems associated
with compensation and venting of the close coupled motors.

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4.2.2 TRACK DRIVE CONTROL SYSTEM
The philosophy of using swash plate pumps to control the speed and direction of rotation
of the track drive motors is conceptually good. There is effectively a power match
between the pump and load which is highly efficient and will generate little heat. The
only potential concern would be that the pilot pressure control of the motor displacement
or swash provides sufficient sensitivity. There also does not appear to be an auto-
tracking, auto-heading or product following capability usually found on post-lay cable
burial machines although this should not be difficult to implement at a later date. There is
no provision for sensing the motor drive sprocket speed. This is very useful information
for controlling a sub-sea trencher.

4.2.3 CUTTER DRIVE CONTROL SYSTEM

The method of control of cutter speed is similar to the Track Drive control system except
that the swash of both of the pumps, each supplying a cutter drive motor, are controlled
by a single proportional pressure control valve. This is not ideal as both of the cutter
motors are connected to a common shaft. The potential problem is that it is unlikely that
the response of two different pumps to the same command signal will be identical. This
will result in one motor wanting to rotate faster than the other. This issue will need to be
discussed and resolved with the pump/motor manufacturer, Rexroth. Similarly to the
track dive system it is useful to have an indication of the motor rotation.
Recommendations
Discuss, resolve and design an engineering solution to synchronise the motor speeds and
flow requirements.

4.2.4 AUXILLIARY SYSTEM

As previously discussed each of the HPU close coupled pump sets a is fitted with a
variable displacement constant pressure pump. These supply the electro-hydraulic valve
packs and the diver operated manual valves. It is impossible to determine or verify how
this is all interconnected or which valve in which valve pack controls what function. The
latest hydraulic schematic received form Subtrench Pty does confirm that there are four
electro-hydraulic valve packs rather than the three units that the original schematic
indicated. However when trying to verify the accuracy of the schematic relative to the
one valve pack that was most accessible inaccuracies were found. Further investigation
would be impossible without expending time which was felt to beyond the scope of the
task brief.
It would have taken a lot of time because all of the electro-hydraulic valve packs and the
diver operated valves are mounted under and around the top of what was once going to be
the docking point mounting for the diver-less launch and recovery system. Access is
extremely limited and what space is available is full of hydraulic hoses connected the the
valve packs and the diver operated valves.
The following series of pictures clearly illustrate the accessibility problems involved. It is
estimated to change one of the valves one of the upper valve packs would probably
require one to two days because the complete valve chest would require removal. It
should be noted that this estimate is based upon it being unnecessary to remove the

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umbilical termination junction box. If one of the lower valve packs should require
servicing then the upper valve pack would have to be removed first.
It is quite apparent that the valve packs were assembled off the vehicle and then installed
before installing the hydraulic fittings and hoses. As can be seen in one of the
photographs the hydraulic base of the valve pack is manufactured from carbon steel
(painted where accessible after installation) and electrical valve enclosures manufactured
from stainless steel. The base manifold is welded to the stainless steel enclosure!

View of the top two valve packs and one bank of diver operated valves looking aft from
the Stbd. Side. The edge of the umbilical JB can be seen in the lower right corner.

View from the top starboard side of the diver operated valves and the upper valve pack
below.

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View from the starboard looking at the aft of the electro-hydraulic valve packs.

As has been previously stated the information on the hydraulic schematic received from
Subtrench Pty. is incomplete but it is suspected that load control valves are fitted in the
electro-hydraulic valve pack to lock load supporting actuators in there desired position.
This is a non-preferred solution as any hose failure between the valve and actuator will
cause the load to drop in an uncontrolled manner. However it is suspected that the diver
operated valves are tee’d into the lines between the load control valves and the actuator.
This could result, when one of the burial tools is in the stowed position, with the tool
dropping uncontrollably if the diver operated valve was inadvertently operated when the
system was on deck. If this is the case it is suggested that this presents an unacceptable
risk to personnel and capital equipment.
What has been established is that when both auxiliary pumps are not required to power
any of the auxiliary functions all of the pump flow is re-circulated through one of the
valves in the valve packs. This is done to stop the pump running at ‘dead head’ at high
pressure however this practice could result in undesirable heat generation within the
hydraulic circuit. As the controller for the pump can also be used as a load sense

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controller this may provide a better solution and enable the pump flow to be circulated
through a cooler to further control the hydraulic fluid temperature if required.

All hydraulic fittings and hose ends are manufactured from carbon steel and are
consequentially heavily corroded and will require replacement.

Recommendations
The system should dismantled to enable a proper hydraulic schematic to be defined. The
system should be reviewed to ensure that the system is functional and safe to personnel
and capital equipment. Reposition the valve packs to provide adequate accessibility and
maintainability.

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4.3 COMPENSATION & SYSTEM INSTALLATION
As previously noted there are six compensator fitted to the hydraulic system.
The three compensators on the aft starboard quarter are interconnected with 3/8” bore
hose via quick disconnect couplings. One of the three compensators is then connected to
a rigid suction manifold along side the starboard pump set by a 3/8” hose.
The system is similar on the port side except only two compensators are used. The third
compensator on the port side is connected to a small stainless steel manifold on the centre
line of the vehicle in front of the valve packs. This central manifold is used to
interconnect the two suction manifolds and to accept the case drains from the four closed
loop pumps (two on the port & two on the starboard side). A small accumulator is fitted
starboard forward of the small central manifold to which a useful purpose or function
cannot yet be assigned.

As can be seen in the following pictures the filters are mounted above the suction
manifolds and are additionally higher than the pumps. The pump suction lines loop over
the side of the ‘bath tub’ enclosing the HPU and down into the top of the suction a
manifold.

View showing the pumps filters and the top of the suction manifold.

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View showing the hoses looping up over the side of the ‘bath tub’ and up to the filters.

4.3.1 TECHNICAL ASSESSMENT

As with other elements of the hydraulic installation it shows signs of being rushed with a
consequent lack of attention to detail that is required to produce a reliable and
maintainable hydraulic system.
The suction hoses suck from the top of the suction manifold which is the point that any
air will be. The hoses loop up and over the ‘bath tub’ making a trap for the air to settle
out at the highest point without any facility to be bled. The filters are at a high point and
may provide some facility to bleed air by loosening hydraulic fittings.
What is also of major concern is the remoteness of the compensators, the very low pre-
charge pressure and the inadequate diameter of the hose linking the compensators and
manifold. A one pound per square inch pressure differential will generate a flow of less
than 1l/min through a one metre long 3/8” diameter hose. When one of the Hydraulic
power units are started there is a transient flow demand from the compensation system of
in excess of 95 litres/min. This will result in pump cavitation every time the HPU is
started, irrespective of the depth pressure. It will also occur every time a demand is made
from the auxiliary system pump. Cavitation is extremely damaging and will result in
premature pump failures.
What is also of concern is the difficulty in purging and venting the air from the hydraulic
system. I cannot believe that the air can be adequately bled from the current system
design. Entrained air is also extremely damaging to hydraulic systems especially when
operating in a high pressure closed loop.
The compensation pressure is too low. The purpose of a positively compensated system is
to ensure that the pressure in the hydraulic system never drops below the ambient

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seawater pressure. This ensures that any small leakage is outboard, contaminating the
hydraulic fluid but outboard of the system.

Recommendations
Increase the compensation system pressure.
Close couple the compensators to a suction manifold or interconnect with adequately
proportioned hoses. The compensators should preferably be below the suction manifold.
The suction lines should connect to the underside of the suction manifold.
The suction manifold should have bleed points at the highest point.
Preferably position the suction manifold higher than the pumps.
Consider reversing the orientation of the HPU so that the pumps are at the forward end of
the vehicle to improve layout weight balance and accessibility.
Optimise hose diameter to minimise bulk and improve accessibility.

4.4 HPU MOTOR & COOLING ISSUES

As previously described the close coupled pumps are driven by a 180kW Pleuger electric
motor. These motors were originally designed to be used to power bore-hole pumps. In
these applications the motor is close coupled to the pump and lowered down the bore-
hole motor first and submerged in the water. As the pump operates it draws water past the
motor ensuring that it is adequately cooled by the stream of water flowing past. The
motors will not operate in air for significant periods of time without overheating and
burning out. The motors are liquid filled to provide pressure compensation and have been
used as prime movers in submersible vehicles for over 25 years. They, personally, are not
a motor of choice as they are long and thin to suit the bore-hole applications but there
quality cannot be questioned. They have been used on the ST2 as a legacy from the
Seajet 2000 vehicle. Because of their slenderness and extreme length they can be difficult
to integrate into sub-sea vehicles.
One of the major issues with any sub-sea vehicle is cooling the prime mover. Modern
ROV use custom design motors fitted into finned aluminium casings to provide
maximum power density with efficient cooling. The long thin Pleuger motor with a plain
stainless steel casing can be difficult to cool and because of the length of the windings
can allow local hot spots to develop within the windings which will result in the winding
overheating or ‘burning out’. As a result Pleuger tend to be very conservative in their
installation requirements. It is understood that Subtrench Pty had quoted a cooling flow
requirement of 100m3/hr whether this for the 180kW hydraulic drive motor or the 250kW
water pump drive motor is not clear.
Beyond all doubt the motor must be adequately cooled to function as a reliable prime
mover. The solution adopted by Subtrench Pty was to enclose the motor and closed
coupled hydraulic pumps in a ‘bath tub’ which could be flooded by an external water
source. In the case of the Q7 project the water was provided by water pumps on the
deploying barge.
This arrangement creates accessibility problems for maintenance and servicing of the
hydraulic pumps and hoses besides other installation problems previously discussed. The
enclosure of the motor could, when operating sub-sea, impair the cooling of the motor by
restricting the circulation of water around the motor casing.

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Recommendations
Liaise with Pleuger to determine the motor cooling requirements.
Decide what the operational requirements are for in air operation of the HPU.
Remove any form of hydraulic pump enclosure from the requirement to cool the electric
motors. If necessary implement a separate hydraulic cooling circuit.
Develop and evaluate concepts for motor cooling, water bath, spray bar, closed loop, etc.
Test and develop as necessary.

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5 WATER SYSTEM
There are two Pleuger electrically driven two stage water pumps. Each motor is rated at
240kW and each pump set produces 537m3/hr at a head of 109m. At present each motor
pump set is totally enclosed by an Aluminium tube fitted with an elevated inlet. The
purpose of the elevated inlet is an attempt to draw clean water into the pump to minimise
wear of the pump rotors. In addition the enclosure ensures that all the water drawn into
the pump passes over the motor casing. This simulates the installation of the pump/motor
set in a bore hole and guarantee motor cooling. As the top of the water inlet tube is
approximately 5 metres above ground level the onboard water pumps cannot be used
unless the depth of water is at least 10 metres (estimated value). At this point any water
jetting requirements will have to be supplied by an external supply. In the case of the Q7
project this requirement was supplied from the offshore deployment barge via flexible
hoses.
At present the connection point for the external supply is on the vehicle centreline
approximately 3 meters above ground level. To change from the onboard water supply to
an external water supply diver operated valves have to be operated to isolate the onboard
water pumps and direct the remote supply to the burial tool. There are also valves to
enable the supply of water to be directed to the ‘bath tubs’ surrounding the HPU motors.
The water supply to the burial tools is through two swivel joints which are incorporated
in to the tool deployment swivel at the aft end of the vehicle.

View of the aft of ST2 showing remote water connection point and water pipe work (in
red) and tool deployment swivels either side of the jetting too attachment flanges.

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There is an interconnection tube between the two water pump supplies to balance the
flows and pressures to both supplies to the jetting tools. There does not appear to be any
non-return valves or isolation valves on the pump discharges to prevent one water pump
back feeding the other. The Water distribution pipe work system would appear to be
another system that as been rushed through to satisfy operational expediency. It should be
possible to simplify and rationalise the system reducing the number of valves and volume
of pipe-work.
The aluminium enclosure for the water pump sets is heavily corroded. This is
unsurprising as the combination of unprotected aluminium in conjunction with a carbon
steel structure and pipe-work, bronze pump and stainless steel motor casing in seawater is
a good recipe for corrosion. It would improve accessibility and maintainability
significantly if the motor pump enclosure could be removed as it consumes a lot of space.
At present the feasibility of changing a pump or motor in an operational environment is
not considered feasible.

Recommendations
Review water system distribution design, rationalise to improve functionality and remove
the requirement for diver operated valves.
Investigate the motor cooling requirements with the view to removal of the motor/pump
enclosure.
Review the necessity for alternative external water supply connections other than
centreline aft.

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6 BURIAL SYSTEMS
There is a suite of burial tools that have been designed by SubTrench Pty.
A. A 3 metre jetting tool sword & Depressor designed for the Q7 Project.

B. A 1.3 metre jetting sword.

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C. A 3.3 metre cutter and depressor.

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 D. A 1.3 meter cutter and depressor
The cutter is supplied as a kit of parts which fits to 3.3m cutter head and replaces
the boom of the 3.3m cutter with a shorter version. It is believed that there are
appropriate chains but this should be verified by trial assembly.

They are all attached to the vehicle via pivot bearings at the aft of the vehicle. Hydraulic
rams are used to pivot the tools into the deployed position. There does not appear to be
any ‘kick back’ load monitoring systems or any relief function on the hydraulics to
prevent excessive forces being generated. None of the actuators are fitted with load
control valves (as previously noted in the hydraulic section) which under hose failure or
leakage conditions would result in the tool dropping in an uncontrolled manner.

When the jetting tools are fitted the water is supplied to the burial tools via a rotary
coupling which passes through the pivot point for the burial tool deployment. When the
cutters are fitted the water supply pipe-work has to be disconnected as it appears the
cutter drive motors have to be fitted through the pivot bearings. The depressor which is
fitted behind the cutter is fitted with an array of water jets to clean the cutting cups as the
pass up the back of the cutting tool. It is not clear how the supply of water is effected.

There does not appear to be any documentation for the installation, operation or
maintenance of any of these burial tools.

The cutting tools require that the product is fed into the top of the depressor implying that
the product is fed over the vehicle. Whilst there is a form of product Shute over the
vehicle there is structure obscuring both entry and exit. Even if entry and exit were clear
the Shute design is not compatible with diverless operation.

Recommendations
All burials tools should be trial fitted to the vehicle and any anomalies resolved.
If Oceanteam desire to be independent of Subtrench Pty regarding the design of burial
tools and spares the assemblies should measured and drawn to provide documentary
records.
The burial tool hydraulic circuits should be revised to provide safe load control and load
relief.
Design a product guide system over the vehicle which suitable for diverless operation.

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7 SURFACE ELECTRICS
The electrical system has been adapted from the SeaJet 2000 system. The power
distribution container has six transformers. Four are wired and used for the supplies to the
water pump prime movers and the HPU prime movers. There have been undocumented
modifications to the power supply control system to the main system transformers.

Recommendations
The transformers will require testing.
The complete power distribution system will need to checked through wire by wire to
determine the circuit diagram. (it has already been determined that there are a number of
safety issue to be addressed).
The system will then need to be evaluated to ensure that it is fit for purpose.
Deck cabling and system interconnects will require integrity checks.

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8 UMBILICAL & WINCH
The umbilical winch currently has 570m of umbilical fitted. At present the winch does
not have a spooling mechanism fitted. There are some components which may be the
spooling system and there is a spooling assembly with an integrated ‘heave compensation
system’ of dubious functionality but some investigation will be required to clarify this
situation

There is not a HPU to drive the winch or any associated controls. We do have a manual
for the winch. There is provision for water cooling the inside of the winch drum an
external spray bar is fitted.

Recommendations
The status of the umbilical & slip ring will require verification. (fibres, insulation
resistance, etc.
Review the design of the spooling mechanism/heave compensation system and modify as
required.
Review the winch hydraulic power and control requirements and specify.
Determine winch cooling water supply requirements.

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9 SUBSEA ELECTRONICS AND ELECTRICS
Some elements of the SeaJet 2000 system have been incorporated in to the ST2 control
system, such the prism MUX system and the umbilical junction box. The Prism MUX
communicates to two OMRON PLC, which control of the ancillary instrumentation and
control systems. The overall integrity of the system is poor. It is inadequately fused
which result in safety hazards to divers and also a single failure of one component could
result in all systems associated to fail. The whole design philosophy is flawed. There
significant heat dissipation issues due to the multiple redundancy of power supplies all of
which are un fused

The system has two pressure pods at present because of the inefficiency of the design. It
would appear that the system has been design by someone without any experience or
knowledge of the system requirements of a sub-sea vehicle. As a result of this philosophy
there are multiple connectors into and out of and between the pressure pods and all the
myriad sensors. This is not good design practice. The more connectors there are in a
system the greater the potential for unreliability and poor systems integrity.

The overall accessibility and maintainability of all vehicle systems are also being
compromised by excessively long cables coiled up all over the vehicle.

As an example the temperature sensors fitted to monitor motor temperatures and

hydraulic system temperatures will provide meaning less outputs the cable lengths and
multiple splices will degrade the signal to the point where it is of little meaning.

Recommendations
Use a standard Hitec computer controller system reusing the existing umbilical junction
box and Prism MUX. The existing pressure vessel maybe used if the 100m depth rating is
acceptable. By using this equipment only one pressure vessel will be required.
A complete review of all ancillary equipment and sensors will be required to verify there
efficacy.

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10 SURFACE ELECTRONICS AND SOFTWARE
The control cabin and console is modified SeaJet2000. The majority of the control panels
are acceptable and can probably be reused with the exception of the track drive operator
panel. There is not any provision for individual proportional control of the tracks. The
Human Interface for the track drive system is non-intuitive and should be modified.
The PLC system is adequate and can possibly be reused.

The control software is a standard Scada integration package. The data is poorly
presented over to many screens which would encourage operator error. To make any
input of data into the software such as calibration information or to change the cutting
tool configuration requires the input of a protection password.

Recommendations
Replace the Scada interface with custom written software (i.e. Poseidon similar to OJ900)
This will provide the same data acquisition facility that has proven very useful on the
OJ900 .

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11 SUMMARY
Before commencing any design and engineering works to bring the system up to an
operational state it important that the senior management within Oceanteam decide what
functionality they want to achieve within practical engineering, financial and timescale
constraints.

Once a final specification has been agreed it is important that a design & engineering
team is dedicated to the project to ensure that focus and design clarity is maintained. The
project should then driven by engineering requirements & objectives and not by
expediency.

The ST2 is the basis for a robust trenching machine. It is believed that the basic chassis
track structure is of sound design and construction.

The hydraulic and water system motors and pumps are of excellent quality and appear to
be in good condition and have done very little work.

The conceptual design of the tool deployment pivot and tool attachment appears sound
but the practicality and maintainability of the system is unproven until all the tooling has
been trial fitted and functionality verified.

The installation and location of the equipment on the vehicle structure is frankly abysmal.
It is inaccessible and un-maintainable.

The ancillary hydraulic system and valve packs should be scrapped and redesigned once
it has been established what functionality is required of the vehicle. They can be replaced
with much smaller and compact valve pack assemblies. This will provide better
flexibility for installation and provide better accessibility and maintainability. Although
this sounds extravagant it should be possible to design manufacture a single multi-station
valve pack for circa £6k.

The electrical and control systems are a poorly executed adaptation of the SeaJet 2000
system with in many areas no documentation and others potentially unsafe. The simplest
solution would be to rework the complete system as recommended in the appropriate
sections of this report.

In order to fully understand the status and function of the system it is recommended that
the system should be dismantled back to the basic chassis and track frames to enable a
full assessment of the work to be done.

Page 28 of 28