Damage StabilityDamage Stability•Damage due to collisions, Damage due to collisions,

subdivided into 3 types;subdivided into 3 types;

•High energy-High energy- These are These are increasingly rare, but ships due increasingly rare, but ships due occasionally collide at right occasionally collide at right angles, going full ahead.angles, going full ahead.

•Moderate Energy-Moderate Energy- penetration penetration no more than 1/5 the beam no more than 1/5 the beam transversely or penetration of 10' transversely or penetration of 10' + 3% of LWL or a vertical + 3% of LWL or a vertical penetration of the vessels depth.penetration of the vessels depth.

•Low Energy-Low Energy- minor damageminor damage such as an allision with a dock or such as an allision with a dock or tugboat working between frames tugboat working between frames too hard.too hard.

Damage StabilityDamage Stability

• It is the moderate energy collision that It is the moderate energy collision that is of most concern to the ships officer.is of most concern to the ships officer.

(WHY?)(WHY?)

• In this situation the survivability of the In this situation the survivability of the ship is based in large part upon the sea ship is based in large part upon the sea state and the vessels stowed condition state and the vessels stowed condition in addition to the damage sustained.in addition to the damage sustained.

Damage StabilityDamage Stability• Effects of hull damage must include Effects of hull damage must include

an investigation of the following;an investigation of the following;

• Loss of Reserve Buoyancy Loss of Reserve Buoyancy

• Loss or Gain in Transverse Loss or Gain in Transverse BuoyancyBuoyancy

• Loss in Longitudinal Hull Loss in Longitudinal Hull StrengthStrength

• Is it possible for a flooded vessel to Is it possible for a flooded vessel to increase "Initial Stability?"increase "Initial Stability?"

Effects of flooding on Transverse Effects of flooding on Transverse StabilityStability

Two methods are used to Two methods are used to approach the problem of approach the problem of flooding on Transverse flooding on Transverse

Stability.Stability.

•Lost Buoyancy MethodLost Buoyancy Method

•Added Weight MethodAdded Weight Method

Damage StabilityDamage Stability• Lost Buoyancy Method-Lost Buoyancy Method- Water that Water that

enters the vessel is considered to be enters the vessel is considered to be still part of the sea, buoyancy of the still part of the sea, buoyancy of the flooded space is lost. This method is flooded space is lost. This method is used by ship designers and MARAD.used by ship designers and MARAD.

• Imagine that the flooded space was Imagine that the flooded space was never built. Only the intact portions of never built. Only the intact portions of the vessel adjacent to the flooded the vessel adjacent to the flooded compartment are contributing to the compartment are contributing to the vessels buoyancy. vessels buoyancy.

Lost Buoyancy MethodLost Buoyancy Method• Since buoyancy has been lost it must be Since buoyancy has been lost it must be

regained by an increase in draft, regained by an increase in draft, therefore the vessel will sink until it therefore the vessel will sink until it displaces the volume of the flooded displaces the volume of the flooded compartment.compartment.

• This will increase KB and decrease BM. This will increase KB and decrease BM. (WHY?)(WHY?)

• With the increase of Draft KB is With the increase of Draft KB is increased.increased.

• In the Equation BM=I/V, “V” remains In the Equation BM=I/V, “V” remains constant or may increase but “I" will constant or may increase but “I" will

decrease because the area of the decrease because the area of the waterplane is decreasedwaterplane is decreased

Damage StabilityDamage Stability

There are no hard and fast rules that There are no hard and fast rules that apply to the effects of flooding on apply to the effects of flooding on

Transverse Stability. However broad Transverse Stability. However broad conclusions can be made by conclusions can be made by

reviewing certain situations that can reviewing certain situations that can occur which affect the change in the occur which affect the change in the

value of BM and KB.value of BM and KB.

Such as the amount and location of Such as the amount and location of

““Intact Buoyancy”Intact Buoyancy”

““Intact Buoyancy”Intact Buoyancy”• Spaces within the flooded Spaces within the flooded

compartment which exclude water. compartment which exclude water. (See LaDage Page 200 Figure 85)(See LaDage Page 200 Figure 85)

• The location of the intact buoyancy is The location of the intact buoyancy is extremely important. For example if extremely important. For example if a hold is flooded, but the adjacent a hold is flooded, but the adjacent double bottoms remain intact and double bottoms remain intact and are empty the loss of reserve are empty the loss of reserve buoyancy would be less, therefore buoyancy would be less, therefore limiting both an increase in draft and limiting both an increase in draft and limiting the rise of “B”. limiting the rise of “B”.

Intact Buoyancy Intact Buoyancy

Intact Intact BuoyancyBuoyancy

• The decrease of BM will remain the The decrease of BM will remain the same as before because the loss of same as before because the loss of the AWP is the same. There is an the AWP is the same. There is an increase of KM when intact buoyancy increase of KM when intact buoyancy is below the surface of the flooded is below the surface of the flooded area, such as intact double bottoms.area, such as intact double bottoms.

• When the intact buoyancy is at the When the intact buoyancy is at the surface of the flooded area, the loss surface of the flooded area, the loss of the AWP is reduced, thus of the AWP is reduced, thus decreasing the loss of “I”,”BM”, decreasing the loss of “I”,”BM”, “KM”, and “GM” (“KM”, and “GM” (See LaDage Figure 85 See LaDage Figure 85 center diagram of 3 on page 200.)center diagram of 3 on page 200.)

Permeability of Flooded Permeability of Flooded SurfaceSurface

• Permeability of Flooded Surface- Permeability of Flooded Surface- percentage of the total surface area percentage of the total surface area of the flooded compartment which of the flooded compartment which can be occupied by water. For can be occupied by water. For example if a compartment were example if a compartment were externally framed so as to be free of externally framed so as to be free of frames, support beams, etc. and frames, support beams, etc. and contained no cargo the permeability contained no cargo the permeability of the area would be %100. of the area would be %100.

Permeability of Flooded Permeability of Flooded SurfaceSurface

•Any reduction in permeability Any reduction in permeability of the space will reduce the of the space will reduce the

loss of waterplane area, loss of waterplane area, resulting in a reduced loss of resulting in a reduced loss of “I”, “BM”, “KM”,“I”, “BM”, “KM”, and and “GM”.“GM”.

Damage Stability Lost Buoyancy MethodDamage Stability Lost Buoyancy Method

Damage ControlDamage Control

Whether or not a vessel will suffer lost Whether or not a vessel will suffer lost GM after flooding depends uponGM after flooding depends upon;;

1.1. Extent of lost waterplane area.Extent of lost waterplane area.

2.2. Location of intact buoyancy.Location of intact buoyancy.

3.3. Permeability of flooding surface.Permeability of flooding surface.

Damage ControlDamage Control

• The ships officer may be able to The ships officer may be able to mitigate the loss of GM by;mitigate the loss of GM by;

1.1. Reducing the area of the flooded Reducing the area of the flooded surface.surface.

2.2. Flooding intact spaces below the Flooding intact spaces below the surface.surface.

3.3. Reducing the permeability of the Reducing the permeability of the flooded surface. flooded surface.

Damage ControlDamage Control

It must be emphasized It must be emphasized that any change in the that any change in the value of GM depends value of GM depends upon the individual upon the individual situation and the situation and the individual vessel !individual vessel !

Added Weight MethodAdded Weight Method• The added weight method assumes The added weight method assumes

the water entering the vessel to be the water entering the vessel to be added weight thus affecting the added weight thus affecting the position of position of “G”“G”..

• If the compartment does not have If the compartment does not have free communication with the sea, for free communication with the sea, for instance a rupture which DC crews instance a rupture which DC crews have repaired, or flooding from have repaired, or flooding from firefighting, the only possible method firefighting, the only possible method of approaching the problem is of approaching the problem is through the added weight method.through the added weight method.

Free Communication with the Free Communication with the SeaSea

• If the compartment does have free If the compartment does have free communication with the sea either communication with the sea either method may be used to make method may be used to make damage stability calculations.damage stability calculations.

Added Weight Method General Added Weight Method General AssumptionsAssumptions

1.1. G will almost always move down. The only G will almost always move down. The only exception being when there is exception being when there is considerable intact buoyancy in the lower considerable intact buoyancy in the lower part of the vessel.part of the vessel.

2.2. There will be a virtual rise in “G” from free There will be a virtual rise in “G” from free surface that is increased with permeability surface that is increased with permeability and beam.and beam.

3.3. There will be an increase in draft with a There will be an increase in draft with a corresponding rapid decrease in KM for corresponding rapid decrease in KM for merchant vessels at lighter drafts and merchant vessels at lighter drafts and slight increases of KM at or near load slight increases of KM at or near load draft. (See hydrostatic Tables)draft. (See hydrostatic Tables)

Added Weight MethodAdded Weight Method