Survivability Features in New Design Ships
Commander Sanjay Varma, IN, (Retd) General Manager, Ship Building, Jindal ITF Limited,

This paper has attempted to provide an insight on vital issues related to the survivability features of the ship. With more emphasis being placed on survivability, ‘damage control’ will thus become a high priority in the overall design effort to build better ships for the users.

With the shrinking defence budget and corresponding reduction in manpower, novel system designs and automated decision aids would be required for future designs. The paper has addressed the ship, system and equipment design features to provide effective shipboard survivability features. The objective of survivability features in new design ships is to achieve incorporation of highest degree of survival features to ensure highest potential for maintaining operational readiness. Further, to preserve the war fighting capability of the ship both in hostile and peacetime environments while in commission. Considerable thoughts have gone in by the naval ship designers to provide the best possible survivability features during the design stage. A great deal of lessons have also been learnt after the Falkland and Gulf wars, which has resulted in thought provoking solutions to provide highest degree of survival features both for the vessel and men. Few of these are enumerated below:

Passive Defence Measures
The passive defence measures that can be achieved by reducing the detectability of the ship, by employing enhanced stealth features like:
  • Reduced radar cross sections
  • Reduced infra red signatures
  • Reduced noise signature
  • Employment of extreme low frequency emitter (ELFE)
  • Suppression methods
Effects of Damage
The damage to the ship can occur both during peacetime and battle conditions. The effects caused by the threats are categorised in a more structured manner as follows:

Primary weapon effects: The primary effects of the weapon are blast, fragmentation, shock, and envelopment by nuclear, chemical biological agents.

Secondary weapons effects: The secondary effect due to weapon could result in physical damage to structure and equipment, flooding, fire, heat, smoke, explosive gas, and toxic atmosphere.

Impact on ship and systems: The effect of these weapons could result in loss of buoyancy, stability, structural integrity, combat capability, mobility, protective systems, personal and equipment.

Design Measures to Contain Effects of Damage
The ship is designed to afford a certain degree of protection against the threats. The survivability philosophy is to provide barriers, containing the threat effects within a volume that can be managed by ship’s staff. Many survivability features tend to add complexity to the ships operation. Basic survivability principles are incorporated into the ship design and include:
  • Fire zones
  • Enhanced damaged stability
  • Improved structural integrity
  • Dispersal of propulsion machinery
  • Redundancy and dispersal of electric power generating machinery
  • Zoning of power distribution system
  • Splinter protection
  • Shock protection of equipment
  • Separation of major component of segmented systems like pumps, piping or cable path
  • Multiple connections
  • Adaptation of Total Atmospheric Control System (TACS)
  • Multiple citadels
  • Zoning of weapons
Effects of Fire & Smoke
The limitation and restriction posed due to fire and smoke are:
  • Smoke is lachrymatory, choking and dense
  • Personnel need to be evacuated from affected sections
  • Visibility in damaged section severely affected
  • Fire can spread rapidly
  • Toxic fumes from burning material
  • Structural strength could be affected resulting in impeding damage control operations
Smoke & Fire Containment
In order to save loss of lives and systems, it is important the careful assessment and serious thoughts need to be given at the design stage. A couple of these requirements are enumerated below:
  • Ship divided into discrete fire zones
  • Containment of air circuits within fire zones
  • Fire zone boundary and fire plans for ship
  • Smoke curtains for access openings on communication deck
  • Smoke clearing fans
  • Fire detection and suppression systems integrated to
  • IDSACS
  • Careful choice of FR materials
  • Photo luminescent markings on escape routes and isolating valves
Zoning Principles
To restrict the damage in the event of casualty, it is prudent that the ship as a whole and the systems be divided in such a fashion that there is always a redundancy. To achieve this, the concept of zoning needs to be incorporated at the design stage as listed below:
  • Hull and superstructure divided length wise into number of zones with a maximum length of 30 metres depending on the size of ship
  • The combined length of any two adjacent zones is not to be less than 30 per cent nor more than 50 per cent of the water line length of the ship
  • The zone end boundaries are to coincide with main water tight bulkheads and are to be continuous from keel to the highest superstructure deck where this is impracticable the bulkhead may be stepped
  • As far as possible each major system together with its support equipment and services is to be arranged as a compact stand alone unit
  • Each zone has to have its own air filtration and air distribution system
  • Each zone is to be self contained to provide emergency support for the crew
  • Zone boundaries should be fire resistant if emergency cross connections are to be provided between zones fire proof closing arrangements operable from both sides are to be provided at zone boundaries and are normally to be kept open
Fire Divisions in Fire Zones
The fire zones and compartments within can be divided into two divisions i.e. ‘A’ Class divisions and ‘B’ Class divisions. The high-risk compartments categorized in ‘A’ Class divisions are machinery compartments, galleys, operation room, inflammable stores, magazines etc. Secondary structures/compartments like bulkheads of main passageway fall in ‘B’ Class divisions.

Escape Routes
It has been experienced that casualties in ships are more due to secondary effect than primary effect. Access plan thus plays a vital role at the time of design. Due to want of ideal escape routes lot of loss of life have been reported in the past. To achieve a meaningful and optimal access plan, following parameters needs to be given a closer look:
  • Compartments with 40 or more men are to be provided with two widely separated standard access
  • Where sloping ladders are fitted to provide vertical access, landings are to be extended to at least one meter from both the root and head of ladder
  • Where vertical ladders are fitted adequate clear space is to be arranged for personnel to ascend and descend whilst wearing breathing apparatus /protective clothing
  • The means of escape should be as directed as possible, easy to find, of adequate width and provide a fire shelter
  • There are to be at least two accessible to the upper deck within each zone
  • Two widely separated means of escape are to be provided for each machinery space
Fire Fighting Arrangements
Fire as we know is the biggest enemy of mankind as also the greatest friend. To enable prevention and containment of the fire, an effective system needs to be installed onboard ships. Few features, which are considered essential, are:
  • Auto fire detection and alarm system
  • Auto initiation of fixed fire fighting arrangement in magazines
  • Remote stations for initiation of fire fighting arrangement in machinery compartments
  • Adequate equipment for manual fire fighting and personal safety
  • Thermal imaging camera
  • Breathing apparatus
  • Wire free communication
  • Elsa sets
  • Fire suits
Smoke Clearing Arrangements
During the Falkland war, one grave omission in design, which came to light, was smoke clearance consequent to fire. Several casualties were reported due to lack of adequate arrangement for smoke clearance. Therefore, it is the most essential from personnel safety that elaborate arrangements are made and requisite smoke clearing system is considered and catered for in the design. The features, which merit consideration, are:
  • Smoke clearing system to be provided on a zone basis. Two dedicated trunked smoke clearance system per zone
  • Systems are situated such that smoke in individual deck spaces can be evacuated without contaminating non-affected areas
  • Smoke clearing system may consist of an axial flow fan with necessary ducts, solenoid quick closing valves and weather terminals
  • Hot gas fans capable of withstanding 250
  • C temperature for one hour may be selected as per requisite specification
  • Provision to be provided to enable an operator to operate the fans in both individually and remotely from DCHQ
  • All dedicated smoke clearance exhaust trunkings are to be watertight and of galvanized steel construction
  • System discharges must be sited well clear of NBC filter intakes
  • Based on the number of sections portable fans with flexible ducts are also to be catered
Flooding Control & Dewatering Management
Serious damage to underwater hull due to explosion or collision can seriously impair the ship. To avoid such situations, it is important that the ship have commensurate mechanism for flood warning and draining out arrangement. Few points for rumination by designers are:
  • Flood warning and flooding status monitoring
  • Adequate pumping out arrangement (fixed and portable) for each water tight sections
  • Emergency diesel driven pumps
  • Spring loaded valves for draining of flooded water to lower decks
Shock Protection
The secondary damage due to shock can have a cascading effect on the ship as a whole. To avoid such damage, it is important that the basic design cater for shock strength of equipment as well as structures. The points to be pondered are:
  • Inherent shock strength of equipment
  • Shock mounting of equipment
  • Shock considerations for system design commensurate to shock standards specified for composite equipment
  • Shock analysis for important systems through Finite Element Analysis
  • Greater attention on structural details
Splinter Protection
To avoid the damaging effect that a splinter can have on the ship system and structures, following needs to be cogitated at the time of design:
  • Vital compartments to be well encased in hull
  • Cable and wave guides to be routed through inside
  • of mast
  • Exposed runs of cables, wave guides and mechanical parts of antennae to be protected
  • Zoning of ship with special bulkheads to limit damage to narrow sections of ship
Citadel and Gastight Integrity
For protection of men and material against the threat of NBC, it is of paramount importance that the ship be so designed that the gastight integrity needs to be maintained, which would provide adequate protection clubbed with water wash down arrangement and NBC suits. Following needs to be catered during design:
  • Simple user-friendly citadel
  • Easy to maintain
  • Improved gastight integrity by design
  • Multiple citadels
The above requirement of the users can be achieved by adopting Total Atmospheric Control System (TACS). The essential features of TACS are:
  • All fresh air induction in ship through AFU’s both in open and close down condition
  • Considerable reduction in number of openings for air inlets/exhausts
  • Enhanced gastight integrity due reduced number of openings
  • Citadel maintenance load considerably reduced
  • Citadel quick and easy to close down
  • Recirculation of air through odour filters
  • Separate ventilation for compartments of inflammable or volatile substance
  • Ship fully air conditioned except for machinery spaces
  • Bleed off part of air to machinery compartments
Integrated Damage Surveillance and Control System (IDSACS)
With the technology changing at a very fast rate, considerable gadgetries are available, which would help is assessing the damaged situation onboard ships. It is, therefore, essential that such equipment or gadgetry be considered for installation at the time of design for quick reaction and assessment of the damaged situation and surveillance. One such system available in international market is Integrated Damage Surveillance and Control System, which has following features:
  • Alarms
  • Fire and smoke
  • Citadel breach or pressure loss
  • Flooding
  • Magazine temperature
  • Incidental display
  • Fire
  • Flooding
  • Portable laptop for situation reporting
  • Status display
  • Doors and hatches
  • Prewetting systems
  • Fire pumps/system valve
  • Tank level system valve
  • AFUs and Vent fans
  • Dewatering system
  • Citadel pressure
  • Magazine display
  • Controls
  • Crash stopping of fans
  • Fluid transfer
  • Start/stop salvage pumps
  • Monitoring stations
  • Controls in DCHQ
  • Additional controls in section bases
  • Expert system for stability management
  • NBCD trainer
When a warship of future is hit with a weapon, the damage sustained by the ship should be bare minimum. The ships underwater structure should be strengthened to provide more protection against underwater shock. Internal arrangements must incorporate placement of double skin bulkheads around critical spaces. Equipment arrangements must provide more separation and more redundant paths for electrical and machinery systems.