An insight into various Damage Stability Standards

Scope• Damage Stability an Introduction

• Evolution of Damage stability rules

• Comparison of damage lengths

• Comparison of other damage criteria

• Probabilistic analysis of damage Stability

• Damages Post WW II – Change of threat

• Latest developments

Introduction• Terms associated with Damage stability –

– Susceptibility• Signature management• Countermeasure

– Vulnerability• Impairment after damage• Ability to recover

– Survivability• Positioning of bulkheads• Location of damage control deck• Openings in WT bulkheads• System Designs

History of Damage stability rules• 1947- Study by BuShips

– 24 ships with torpedo hits during World War II analysed– Length Criteria developed ( 15 % LBP)

• Adoption of Wind Criteria from Sarchin and Goldberg, 1962– Pacific Typhoon 1944 , US lost 790 men and 3

destroyers .

Comparison of Damage Stability Criteria –

Deterministic Approach

Basic considerations for stability after damage

• Length of damage.

• Residual Reserve of buoyancy (only Considered till WT bulkhead deck)

• Angle of list

• Ability to resist wind and roll

After effects of Damage

• Parallel sinkage.

• List

• Trim

• Reduced ability to resist wind and roll

30% loss of ROB

Length of damage criteria

• 12.5% for other ships

Hospital ships/ Troop carriers

• UK/US – Bkhd to be WT upto deck above apex of V – line

• Japan – No Bkhd penetration below damage control deck

• Canada – No WT door/hatch below damage waterline on main WT bulkheads.

• Germany - Doors below Bulkhead deck may be given along ships center line

Provision of Openings

V Line – US Navy

V Line – UK Navy

Merchant Navy

• WT sliding doors – allowed below damage waterline– Electrically/ hydraulically operated– Remote operability

List/Loll after DamageCountry UK US JAPAN ITAL

YCANADA FRANCE GERMANY

Angle of List/ Loll

< 200 < 150 - < 150 < 150 < 200

<150 after cross flooding

< 250

Cargo Vessel

Passenger Vessel

25 0 - 300 7 0 - 150

SOLAS

Roll back angleCountry UK US JAPAN ITALY CANADA FRANCE GERMANY

Angle of List/ Loll

150 100

for a 5000 t ship

Calculates as per Sea State

- < 150

for a 5000 t ship

150 -

RUSSIA

Roll amplitude = kX1X 2Y

K – Appendage factorX1 – B/TX 2 - C B

Y – sqrt(GM)/B

Post Damage - Roll curve US Navy

Origin – Roll back angle

• Not clearly specified in any literature.

• 250 roll observed during WW II – intact ships

• Ships roll depends on –– Sea State– GM of the Ship– Geometry of the Hull

Japan & Russia – Considers Sea State for calculation of roll

Other Criteria

Damage stability philosophies

• Canada – – Heel after flooding kept min. expending least Reserve

buoyancy (Cross flooding)

• Germany – – Probability analysis for assessment of damage effects , if

Ship design not satisfying their criteria

• Italy - – Survivability - primary concern choosing dimensions, hull

form, subdivision and systems– Ability to continue mission. (Systems design)

• United Kingdom – – Placement of transverse bulkheads, adequate reserves

of buoyancy and stability – Preserve mobility and operational functions.

• Australia - – Adopted from US navy – changed loading cond.

Damage stability philosophies

Probabilistic Damage Stability – SOLAS (MSC 281(85))

Calculation Method

• Damage is assumed to have occurred • Probability of damage location and extent p • Probability that the vessel can survive s• Probability of vessel surviving this damage p . s • Attained Subdivision Index (A)

– Total probability of survival as sum of all probabilities A = Σ (pi . si)

• R is the required subdivision index – Formula based on length, No. of passengers R

• Requirement is that A > R A > R • Probabilities are based on actual statistics of casualties

Inputs for Pi• 3 loading cases considered.

– Deep– Partial– Light

• Max. adjacent zones to damage• Longitudinal zone location & Subdivision• Transverse subdivision

Inputs for Si• Equilibrium heel angle

• Down flooding angle

• GZmax before down flooding.

• Range – From equilibrium angle to downflooding angle

• Flooding stage – Before reaching equilibrium

Damages Post World War II – changes in threat

Post world War II

• Underwater mines , Korean war – 4 minesweepers lost, larger ships survived damage

but left nonoperational

• Above water combat damage – Exocet missiles , Aerial Bombs– Ships sunk by firefighting water

• Collision - Routine operation

Summary - Major damages post WW II

Warship Damage Stability – Latest developments

Latest Trends in ship design• Increased payload to displacement ratio

• Enhanced Weapon and sensor capability, Reduced RCS

• Reduction in structural weight

• Design for Enhanced Survivability

• Capability to continue mission

Probabilistic approach• Susceptibility ( PH ) – Inability to intercept and

being detected (Signature management/ Countermeasures)

• Vulnerability ( PV ) - Impairment during a damage

• Killability, PK = PH x PV

• Probability of Survival = 1 - PK

Probabilistic approach

• Point of hit– Depends on Weapon

• Exocet hits at Waterline level• Harpoon hits at Superstructure level.• Heat seeking missiles on funnel and engine

area

• Length of damage – Warhead used.

Survivability Index for naval Ships

One of the proposed model of survivability index

Conclusion

• Ship design for – Vulnerability & Survivability

• Optimal watertight compartmentation• Variety of damage scenarios and

operational/environmental conditions.• Location of Damage control deck

– Restrictions • Space requirements for accommodation,

weapon, vital systems• Minimization of structural weight

Very difficult without an

optimisation algorithm.

Way Ahead

• Database of previous damages – effects/causes

• Understand and define our priority-– Survivability ( Bhkd positioning, form)– Fight Hurt ( System design)

THANK YOU

Type 21 Frigate- HMS Ardent - hit by 1,000 lb aerialbombs- Sank

Type 42 Air Defence Destroyer - HMS Sheffield - AM39 Exocet. - Warhead failed to explode but Caused Uncontrollable Fire/Sunk

• Ships designed for critical damage of 15 % LBP survived

Extent of damage• Longitudinal-

- 15% LBP along the length • Transverse-

- Only one side of the double bottom tank

• Vertical-- Till the bulkhead deck

15% LBP Damage Simulation

15% LBP Damage Simulation

Wind Criteria

Dynamic Stability Simulation

Costa Concordia- Italian Cruise ship sinking

NAPA Simulation-Costa Serena

NAPA Simulation-Costa Serena

NAPA Simulation-Costa Serena