A Watt, Submarine Support Management Group (BMT Defence Services), UK
E Ofosu-Apeasah, Ministry of Defence Salvage & Marine Operations Project Team, UK SUMMARY
One of the requirements for a dived submarine is the ability to recover from a significant incident such as a fire or collision. In these circumstances, the recovery from the incident may require the submarine to surface and depending on the severity may lead to the submarine becoming disabled on the surface. In such instances, the submarines’ crew will need to stabilise the situation before additional external support is available.
The surfaced disabled submarine cannot be considered safe until it is successfully recovered to a safe haven which initially depends on the equipment onboard. However, a number of recovery methods such as, snagging the anchor or rudder, can provide additional options to support the recovery. The behaviour of the submarine under these alternative recovery methods is not fully understood and is being investigated via computer and tank modelling in parallel with full scale trials.
1. INTRODUCTION
1.1 SALVAGE & MARINE OPERATIONS PROJECT TEAM (S&MO)
The UK Ministry of Defence (MoD UK) S&MO is part of the Defence Equipment and Support organisation with a complement of about 60 civilians, led by the Chief Salvage & Mooring Officer.
The primary role of S&MO is to provide tri-service marine salvage, ocean and coastal towing, heavy lift and fleet operational mooring capability worldwide. S&MO is a first responder organisation, with the ability to provide personnel and equipment within defined readiness parameters to a maritime incident, with the first elements being ready to deploy within 6 hours of the initiating event.
S&MO operational personnel are sponsored reserves who are required to hold and maintain both their commercial industry qualifications and military training capabilities in various disciplines, such as marine engineering, seamanship, naval architecture, salvage, mooring and diving in readiness for their deployment.
This offers flexibility in the deployment of S&MO personnel in support of maritime incidents ranging from peacetime evolutions working with contractors’ right through to hostile military theatres working directly alongside military personnel.
1.2 SUBMARINE SUPPORT MANAGEMENT
GROUP (SSMG)
The SSMG is an industry team with Babcock as prime contractor, supported by the BMT Group and SEA, collectively providing design and engineering technical services to the in-service Royal Navy submarine flotilla.
The Submarine Engineering Support Contract (SESC), which the SSMG services, is a 10 year contract that runs
until April 2019 between the MoD UK In-Service Submarines Project Team and Babcock.
The SESC evolved out of the MoD’s Transforming Submarine Support Initiative to provide design and engineering technical services. The contract is designed to create an integrated joint team to produce the shared MoD UK In-Service Submarines Project Team and MoD UK Combat Systems Group outputs necessary to deliver submarine availability.
The SESC applies partnering principles to deliver a more sustainable support enterprise, flexible to adapt to changing priorities while able to provide surety of submarine availability and meet the increasing demands for safety assurance.
2. AIM AND SCOPE
Submarines are specifically designed and built with multi-redundancy systems to enable them to operate and navigate safely both on the surface and under water.
Consequently in the event of loss of all electrical and propulsive power when dived, the submarine will still be able to return to the surface by blowing water out of its main ballast tanks using high pressure air banks.
However, if a large quantity of sea water floods into the pressure hull after a catastrophic incident or failure of a sea water system that cannot be isolated, a point will be reached when no action taken by the submarine crew can compensate for the increased weight of flood water and the submarine will sink to the sea bed.
In this instance, provided the submarine is in rescue capable waters, the recovery of the submarine crew will be undertaken by a submarine rescue system. However, this scenario is outside the scope of this paper, which aims to discuss both existing and other innovative methods that may be employed to successfully recover a surfaced disabled submarine to a safe haven.
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© 2011: The Royal Institution of Naval Architects 2.1 SUBMARINE INCIDENTS
Although infrequent, some of the possible incidents that could lead to a submarine becoming disabled on the surface are:
x Fire;
x Collision and grounding;
x Fishing net entanglement;
x Mechanical or material defect;
x Sabotage;
x Radiological;
x Enemy action, etc.
2.2 SUBMARINE INCIDENT LOCATIONS The world’s oceans cover over 70% of the earth’s surface, with about 77% of this being in relatively deepwater, over 3000 metres. The likely location of a submarine incident will be dictated by the type of submarine and its operating area and therefore may occur in one of the following areas:
x Littoral and/or coastal waters with or without host nation support;
x Open oceans with easy access to offshore support vessels;
x Remote open oceans with poor access to offshore support vessels;
x Unfriendly hostile areas without host nation support; and
x Antarctic and Arctic regions.
The subsequent stabilising and recovery options for each of the above areas are discussed later.
2.3 CHALLENGES AND CONSIDERATIONS Some of the challenges and considerations that may have to be overcome in responding to a submarine incident in any of the above areas are:
x Weather and geography of the area;
x State of tide and daylight;
x Speed and timeliness of response;
x Personnel and vessel safety;
x Technical;
x Environmental, radiological and pollution;
x Political and diplomatic aspects;
x Availability of commercial resources;
x Logistical Support;
x Media management and communications; and x Force protection.
3. INITIAL STABILISING ACTIONS
The actions necessary to stabilise the initial situation will be dependant on a number of factors such as; the prevailing sea state, weather and environmental conditions, type and nature of the incident and the extent of disablement, for example, loss of propulsion and manoeuvring capability.
3.1 ACTIONS BY SUBMARINE CREW
The initial response to the incident by the submarine crew will be dictated by their training and experience, the submarine design and equipment onboard. Initial responses to an incident may include:
x Notification of the submarine Operating Authority of the incident;
x Damage control and fire fighting techniques;
x Communication with nearby naval or commercial vessels for support;
x Deployment of a parachute type sea anchor to orientate the bow of the submarine into head seas or wind to reduce roll and rate of drift;
x Anchoring the submarine;
x Beaching the submarine in sheltered waters.
3.2 FLOODING AND LOSS OF BUOYANCY If the submarine has lost or is losing buoyancy through flooding there could be a number ways to alleviate the situation. Submarine crew are trained and exercised in damage control techniques on their vessels and carry damage control equipment onboard such as wooden planks, wooden wedges and hammers which would be used to combat the ingress of sea water.
When the exact location of the damage is known and it is found to be just below the waterline, the submarine can be ballasted or heeled such that the damaged area remains above the surface to limit sea water ingress.
Eductors or pumps can then be used to remove the sea water from the damaged compartment. For minor damage to the main ballast tanks the low pressure blower can be used to maintain a positive differential air pressure and keep sea water out.
3.3 ASSISTANCE FROM NEARBY VESSELS If the submarine is accompanied by a support ship and other surface assets then it may be possible to provide immediate assistance to the submarine. The support ship and the other surface assets could, if required, provide:
x A berthing capability and tailored assistance;
x First aid salvage patching capability from outside the submarine;
x External electrical power supply;
x Communications;
x Fire fighting;
x Low and high pressure air through the high and low salvage valves.
3.4 ASSISTANCE FROM EXTERNAL AND
SPECIALIST TEAMS
In MoD UK it is common practice for specialist personnel, equipment and vessels to be mobilised to support a marine incident anywhere in the world, therefore a disabled surfaced submarine recovery would be responded to similarly.
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© 2011: The Royal Institution of Naval Architects
4. SURFACE STABILISING AND
RECOVERY OPTIONS
The first option available to the submarine crew is the provision of specialist advice and/or first aid assistance to enable repairs to be undertaken on site so that the submarine can transit to a safe haven under its own power.
The main other stabilising and recovery options under the likely incident locations are discussed below.
4.1 LITTORAL, COASTAL OR SHALLOW
WATER AREAS
4.1 (a) Allow The Submarine To Drift
The submarine could be allowed to drift off or along the coast provided that there was no risk of collision or grounding and danger to surface navigation such as fishing nets, wrecks, mined areas etc.
4.1 (b) Use Of A Parachute Sea Anchor
The natural tendency for most surface ships is to turn approximately beam on to the sea and/or wind when disabled or “not under command”. This orientation will often cause extremely uncomfortable roll motions even in lower sea states.
Sea anchors have been used over many years, principally by yachts, fishing and pleasure boats for holding their bow or head into the wind, or to improve their directional stability downwind in adverse conditions.
A commercial variant has been adapted by S&MO with assistance from Para Anchors Ltd, Australia for use with larger vessels and is designed to produce drag and hold the bow or stern of the vessel into the wind or sea, thereby reducing roll and pitch motions and improving crew comfort onboard.
The S&MO parachute sea anchor is designed to be secured to a strong point at the bow of the submarine, either via the mooring bollards, fin harness or rip out tow pendant and deployed over the side. The force generated by the parachute sea anchor during the modelling has been shown to be enough to deploy the rip out tow, thereby enabling responding tugs to recover both the parachute sea anchor and rip out tow line and commence the tow without the need to get too close to the submarine in potentially high sea states. The fin harness and rip-out tow recovery methods are explained in Section 5.
Figure 1 – Photograph of a parachute sea anchor on test with a submarine model
Towing tank and open water trials undertaken by S&MO and QinetiQ have shown that a parachute sea anchor which has been designed to suit the size and displacement of the submarine can change its heading, drift rate and reduce pitch and roll motions. The trials have also indicated that it is possible to change the behaviour and characteristics of the parachute sea anchor depending on the type of material used, shape, size and amount of load impacted on it. A full-scale test of the parachute sea anchor with an operational submarine is planned to be held later this year.
Sea Direction
Buoy Retrieval Line
Parachute Sea Anchor
Bridle & Strop Assembly
Steelite
Figure 2 – Schematic of the use of a parachute sea anchor 4.1 (c) Anchoring The Submarine
The submarine could anchor in suitable water-depths to hold her position and undertake repairs. However, it has been known for submarines to go to sea with their anchor secured in place with a Blake Slip to prevent noise generation from the rattling of the anchor or chain cable against the hawse pipe. However, the fitting of the Blake slip means that the anchor cannot be deployed without first having to put personnel on the casing to release it.
It is considered that for future submarines, the anchoring arrangements should be modified to prevent the potential noise issues and also allow the anchor to be released from inside the submarine.
In the interim period, it is necessary to ensure that submarines do not go to sea with their Blake Slip’s
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© 2011: The Royal Institution of Naval Architects engaged or that they can be released quickly if the anchor
is required.
4.1 (d) Mooring Alongside A Support Ship
The submarine could moor alongside a support ship for assistance. The support ship could then anchor, moor or maintain position by Dynamic Positioning if fitted. The motion monitoring capability of the support ship as well as the design of new intelligent fenders that are capable of transmitting motion data, audible warning alarms and lights indicating the stresses being experienced to the support ship to enable appropriate action to be taken, needs to be reviewed.
4.1 (e) Rigging The Fin Harness
The use of the fin harness is explained in Paragraph 5.6.
If carried, the submarine crew could rig it in readiness for a tow.
4.1 (f) Beaching The Submarine
Should the submarine continue to lose buoyancy and there is a risk that it could sink, then beaching it in shallow sheltered water on a soft sea bed could be considered. For a nuclear submarine the maintenance of the sea water supply for reactor cooling would need to be addressed.
4.1 (g) Towing To A Place Of Safety
The submarine could be towed to a place of safety. See Section 5 for a description of submarine towing methods.
4.2 DEEP WATER AREAS
For the purposes of this paper, deep water is taken as depths exceeding 100m as it is considered that beyond this depth, the submarine is unlikely to be able to use its designed and fitted anchor system. While some of the recovery options in littoral and shallow waters can also be utilised in deep water, only those that are specific to deep water away from the coast are listed below.
4.2 (a) Anchoring
The Deep Water Mooring System (DWMS) has been developed by S&MO for mooring a disabled or damaged submarine of up to 18000 tonnes displacement in depths of up to 3000m in all types of seabed in sea state 8 conditions for a maximum of 30 days.
4.2 (b) Heavy Lift / Floating Dry Dock
If the disabled submarine cannot be repaired in situ to allow it to transit to a safe haven under its own power, then an emergency tow or use of a heavy lift vessel or floating dry dock for recovery could be considered.
5. RECOVERY METHODS
When a submarine is disabled on the surface it is not considered safe until it has been recovered to a safe haven. If the submarine cannot be repaired in situ then the main recovery method is via emergency towing.
5.1 EMERGENCY TOW OF SUBMARINES All operational MoD UK Submarines have a built in emergency towing system referred to as the “Rip-Out Tow.” Other alternative emergency towing methods developed by S&MO are also available depending on the nature of the incident, prevailing sea state conditions and risk of exposure of personnel on the casing in adverse environmental conditions.
5.2 RIP OUT TOW
The MoD UK Rip-Out tow system comprises:
x Rip out pendant;
x Main tow line;
x Tow slip.
The rip-out pendant is a high modulus polyethylene (HMPE) rope which is stowed in a channel that runs from the bow along the casing and up to the top of the starboard side of the fin. The pendant allows the submarine crew to secure a messenger line, passed from a tug, to the pendant eye without leaving the relative safety of the navigation position at the top of the fin.
The tug pulls on the messenger and “Rip’s-Out” the pendant in order to deploy the main tow line. The main tow line is a 100 metre HMPE rope stored in a recess under the submarine casing near the bow.
The tow slip connects the main tow line to the submarine structure and allows the main tow line to be disconnected or slipped by the submarine in an emergency. It is operated via a mechanical linkage that is manually actuated from within the submarine.
5.3 ANCHOR SNAG
The anchor snag method has been developed to enable the submarine to be towed via the anchor chain cable.
The submarine will initially deploy its anchor to a predetermined depth beneath the keel. A weighted wire, which sinks to a predetermined safe depth beneath the submarine, is paid out between two tugs. The tugs approach the stern of the submarine from the port and starboard sides of the submarine. As the tugs move ahead of the submarine the weighted wire snags the deployed anchor chain.
At a safe distance ahead of the submarine, typically 100 metres, the 2 tugs meet and pass the ends of the weighted wire to one tug. The tug holding the 2 eyes of the
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© 2011: The Royal Institution of Naval Architects weighted wire then connects them to its main towing hawser using a suitable shackle. Figure 3 shows a schematic of the complete anchor snag towing arrangement.
For longer tows, a more robust arrangement may be required. Using a tug with an open stern in suitable sea conditions the submarine anchor can be recovered onto the deck of the tug. The main tow line of the tug can then be secured directly to the anchor chain to provide a more secure connection.
Figure 3 – Schematic of a tow using the Anchor Snag methodology
5.4 RUDDER SNAG
If the towing methods normally available to tow the submarine from the bow are inaccessible then other options need to be considered. The rudder snag towing method has been developed to provide an alternative stern towing method.
Two tugs (lead and support) manoeuvre such that one is to port and the other to starboard of the submarine, both aft of the bridge fin. The tug to leeward of the submarine fires a rocket line type device to pass a line to the windward tug over the aft casing between the upper rudder and the fin. The line is attached to a messenger line which in turn is attached to the Rudder Snag System, see Figure 4, with which the tow will be undertaken.
Figure 4 – Schematic of the Rudder Snag system
The windward tug hauls in the line and messenger line to recover and secure the Rudder Snag System such that the chain is approximately central on the casing.
The tugs then move aft towards the stern of the submarine and meet approximately 100m aft of the submarine to enable the ends of the wire to be joined on the lead tug. The lead tug then secures the ends of the wire to its main towing hawser to start the tow. A schematic of the rudder snag methodology can be seen in Figure 5.
Figure 5 – Schematic of a tow using the Rudder Snag methodology
A disadvantage of this method is that the tow is likely to cause damage to the upper rudder which would require rectification before the submarine could return to sea.
5.5 USE OF MOORING BOLLARDS / HINGED CLEATS
If the casing can be accessed then it may be possible to utilise the mooring bollards or hinged cleats by rigging either a wire or protected soft rope pendants into a bridle arrangement for towing. However the sea conditions would need to be benign to safely allow personnel on the casing to raise the mooring bollards/hinged cleats.
5.6 FIN HARNESS
The fin harness was originally intended to be used to hold and prevent a disabled submarine from running ashore in an emergency. However, as demonstrated during the HMCS CHICOUTIMI incident, it can be adapted for towing a disabled submarine. The fin harness system should only be used where the fin has been proved to be able to withstand the loads associated with its use.
Figure 6 – Schematic of a tow using the Fin Harness methodology without assistance from the submarine crew
The fin harness can be deployed either by the submarine crew or deployed by 2 tugs lassoing the fin without the assistance of the submarine crew.
Wire Chain (7m) Wire