Buques En Calla Dos y Volcados

832019 Buques En Calla Dos y Volcados

httpslidepdfcomreaderfullbuques-en-calla-dos-y-volcados 113

S0300-A8-HBK-010

CHAPTERCHAPTER 66

SUNKENSUNKEN ANDAND CAPSIZEDCAPSIZED SHIPSSHIPS

6-1 INTRODUCTION

Ships sink or capsize because they lose their buoyancy or stability through battle and weather damage collision intentional flooding and othemeans The damage makes their salvage more difficult than it would be for an intact ship in the same location Beyond this and the fact thathe ships are supported largely or totally by the ground common circumstances of stranded ships do not apply to sunken ships

Usually ships are salvaged only if sunk in relatively shallow water While it is technically possible to recover ships and other large objectfrom great depths the cost is usually prohibitive The difficulties and cost increase rapidly with depth ships sunk with more than 100 feet ofwater over their decks usually are considered beyond economic salvage although high-value or sensitive cargo may justify their recoverySubmarines because of their construction can be recovered from somewhat greater depths high replacement cost and strategic value may justifsalvage

Salvage of sunken vessels is not usually as time-critical as salvage of strandings A vessel sunk in protected waters or in water deep enougto protect it from surface conditions is unlikely to deteriorate unless severe storms develop More time can be taken to plan and marshal forcefor the salvage effort A ship partially sunk on an exposed coast however is in a situation similar to that of a strandingmdashthe casualtyrsquocondition deteriorates over time Wreck removal and harbor clearance operations involving sunken ships are often urgent because of thnecessity to open obstructed waterways and port facilities

All marine salvage work is a combination of seamanship and engineering In stranding salvage seamanship predominates salvage or clearancof sunken ships requires a greater proportion of engineering The salvage engineer has four principal tasks

bull Predict the behavior of sunken and capsized ships by applying the principles of buoyancy and stability discussed in Chapter 1

bull Determine required lifting andor righting forces

bull Determine effects of environmental forces on the casualty and salvage systems

bull Devise methods of applying forces to right or lift the casualty in a controlled manner

The US Navy Ship Salvage Manual Volume 2 (S0300-A6-MAN-020) discusses righting and raising sunken ships in detail This chapte

provides amplifying information on factors influencing methods of salvaging sunken ships such as sinking conditions and the environment

6-2 SINKING CONDITION

A sunken shiprsquos attitude relative to both the seafloor and water surface is a principal indicator of the complexity of her salvage The magnitudand distribution of ground reaction are the most important elements of a shiprsquos stranding condition Analogous elements for sunken ships are threquired lifting and parbuckling forces The relative degree of submergence is equally important because of its effect on stability during raising

Degree of submergence and distribution of the shiprsquos weight between ground reaction and buoyancy profoundly influence a sunken shiprsquobehavior The position attitude and orientation of a sunken ship can either mitigate or intensify environmental effects Important factors othe sinking condition include

bull Whether the ship is capsized

bull How deeply the ship has penetrated or settled into the bottom

bull Depth of water around and above the ship

bull Damage suffered before during and after sinking

bull Vessel attitude ie list trim contact with the bottom etc

bull Distance to protected shallow waters

bull Degree of submergence

6-



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Sinking often results from flooding following hull damage additional damage may result when the ship strikes or settles on the bottom A diving

survey can provide an accurate picture of the shiprsquos condition but indications of some conditions may be visible from the surface If the

casualtyrsquos masts either converge or diverge the ship may have broken in sinking If one end of a ship sank rapidly while the other end remained

afloat for several hours it is likely that little or no damage occurred to the slowly sinking end and that the vessel lost buoyancy through slow

seepage Differences between water levels inside and outside of a partially sunken ship and between compartments within the ship (as the tide

rises or falls) may indicate the extent of damage to shell and bulkheads

6-3 ENVIRONMENTAL EFFECTS

Environmental effects on sunken ships include responses of the seafloor to loading by the casualty and fluid forces of the surrounding water

In a sinking much of the casualty is exposed to hydrostatic pressure current forces and current-induced scour or silting Work on the casualty

must be accomplished through the water column Wind and weather affect salvors and salvage vessels alike

6-31 Seafloor Effects Effects of the seafloor on a sunken casualty include

bull Gradual sinkage into the seafloor

bull Suction on cohesive seafloors

bull Hull girder stresses caused by uneven support

bull Obstructions presented by the bottom topography

bull Scour

bull Silting

Composition and consistency of the seafloor under the ship and slope of the seafloor near the casualty are the two most important characteristics

influencing seafloor effects The US Navy Ship Salvage Manual Volume 2 (S0300-A6-MAN-020) discusses the general effects of the seafloor

on sunken vessels and lifting operations Paragraph3-73 describes calculation of bottom breakout forces required to break seafloor suction

Silt and mud that settle in the ship constitute weight that must be either removed or overcome during the refloating Removing silt and mud

lightens the ship and makes her behavior more predictable Chapter 5 discusses the use of air lifts and other underwater excavation methods suit-

able for removing accumulated silt from sunken ships The weight of mud varies with the type of soil Table 3-3 lists some typical values for

underwater weightmdashthe weight of the soil less the weight of the displaced water Because of internal voids one cubic foot of soil displaces less

than one cubic foot of water The actual volume of water displaced by a volume of soil depends on the compactness or porosity (ratio of volume

of voids to volume of soil particles) of the soil Porosity ranges from 03 for dense settled sand to 06 for recently deposited loose silt

Mud removed from a casualty is sometimes deposited on a barge or ashore The weight of spoil can be estimated from the change in barge

draft This weight is greater than the weight removed from the casualty because it includes weight of water trapped in the soil The weight

removed can be estimated by multiplying spoil weight by the solidrsquos proportion (1 minus porosity) Wet weight can be determined simply by

weighing a bucket of mud brought up from the wreck if time permits the weight of solids for a given volume of mud can be determined by

drying the mud before weighing A microwave oven is convenient for drying soil samples

6-32 Fluid Forces Fluid forces on a sunken ship derive from the depth of water in which the ship lies and the effects of tide waves swell

and current

6-321 Water Depth Because hydrostatic pressure increases with depth water depth determines the hydrostatic pressures on the casualty bothas it sits and as it is raised The fact that pressure complicates the salvage of sunken ships is a major reason why deeply sunken ships are seldom

salvaged Pressure varies with depth according to the following relationship

ph = γ wd

where

ph = hydrostatic pressure

γ = weight density of water = ρggc (seeParagraphD-41)

d = water depth

6-2



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If depth is measured in feet density in pounds perTable 6-1 Shipboard Manhole Cover Specifications

(ASTM Standards F1142 F1143 and F1144)

Bolted Semi-flush Oiltight and Watertight Manhole Cover Assembly

Type GradePlate

Thicknessin

Deck CutOverall

Size in

CoverOverall

Size in

Numberof Bolts

or Studs

DesignPressure

psi

I 1 1 frasl 4 15 times 23 21 times 29 22 120I 2 3 frasl 8 15 times 23 21 times 29 22 270

I 3 1 frasl 2 15 times 23 21 times 29 22 479

II 1 1 frasl 4 18 times 24 24 times 30 24 89



Rectangular Raised Oiltight and Watertight Manhole Cover Assembly

Type Grade PlateThickness

in

Deck CutOverall Size

in

Cover OverallSize in

Number ofBolts or

Studs

DesignPressure

psi

I 1 1 frasl 4 15 times 23 213 frasl 4 times 293 frasl 4 30 75



II 1 1 frasl 4 18 times 24 243 frasl 4 times 303 frasl 4 34 67



Raised Oiltight and Watertight Manhole Cover Assembly

Type GradePlate

Thicknessin

Deck CutOverall

Size in

CoverOverall

Size in

Numberof Boltsor Studs

DesignPressure

psi







cubic foot and pressure is desired in pounds persquare inch the relationship can be simplified

where

ph

=

γ 144

d

= 0445d (seawater)

= 0433d (fresh water)

ph = hydrostatic pressure lbin2

γ = water density lbft3

d = water depth feet

Pressure acts equally on all surfaces of a sunkenship filled with water Pressure differentials acrossstructures resulting from dewatering of spaces canbe sufficient to cause failureShip decks and bulkheads are designed to withstand

a pressure differential of four to six feet of waterhead greater than the depth of the bulkhead If theship is old has been sunk for a long time isdamaged or the bulkhead is otherwise in poorcondition this pressure differential may beexcessive If the pressure differential is greaterthan six feet of seawater or the strength isquestionable bulkheads should be reinforced byshoring or by building false bulkheads adjacent tothem and placing concrete between the real andfalse bulkheads If concrete is not available densebulk material such as loose stone sand coal oreetc can be placed between the bulkheads toprovide shoring weight

Strength of stiffened and cross-stiffened bulkheads can be estimated by the methods described in Paragraphs 2-22 and 2-23 Unstiffenebulkhead strength is given by the flat plate formulae described in Paragraph 2-5 The following guidelines can be used to estimate strength omiscellaneous structures and fittings under distributed loads

bull A rule of thumb for commercial vessels is that a main deck submerged more than 6 feet must be shored

bull Steel and aluminum watertight doors built to US commercial standards are designed for a uniform pressure of 9 psig glass

reinforced plastic (GRP) watertight doors are designed for a uniform pressure of 5 psig

bull Design pressures and dimensions for watertight and oiltight manhole covers built to ASTM standards are given in Table 6-1

For ships built to US Navy specifications (GENSPECs)

bull Shell and weather deck plating is designed for a hydrostatic load of 500 pounds per square foot (approximately 35 psi or 78 fee

of seawater)

bull Vertical stiffeners on structural bulkheads are designed as pin-ended columns

bull Watertight bulkheads are designed to withstand flooding to the damage control deck Due to their load-bearing requirements

structural watertight bulkheads may be able to carry a higher hydrostatic head

bull An air test schedule indicates test pressure for certain watertight compartments Although they are usually stronger compartmen

boundaries can carry at least the specified pressure The air test schedule for the casualty or for sister ships may be obtained fromthe planning yard squadron maintenance officer or a sister ship

6-



S0300-A8-HBK-010

6-322 Tide Tide is important when salvaging sunken ships for five reasons

bull Depth of water over the deck varies with tide

bull In partially exposed ships downflooding through hatches doors and other openings can occur as the tide rises As the tide falls

larger portions of the ship are exposed permitting work to be performed without diving

bull The buoyancy in partially exposed watertight spaces increases as tide rises

bull The amount of tidal lift is directly related to the height of the tide

bull Water level in partially exposed holds or compartments relative to that outside the ship can give important clues about hull damage

An appreciable time lag between the rise or fall of the water level inside a compartment and that outside the ship indicates slowleakage and relatively small openings in the hull or piping Little or no lag indicates one or more large openings or many smallopenings

Patches cofferdams and other structures affected by either hydrostatic pressure or water depth should be designed for the highest tide likelyto occur during the salvage operation A generous margin should be allowed but not so generous that the freeboard of a full cofferdam inhibitshandling materials from boats into the cofferdam

6-323 Waves and Swells Waves entering a casualty through large openings can be channeled into narrow passages the wave energy is

concentrated and the waves strike obstructing bulkheads or patches with great force There may be a strong and violent surge inside a vesselwhile only a moderate swell is running outside High internal pressures can occur if waves enter the hull or the water inside the casualty isexcited by the waves The rapidly varying water level alternately compresses and expands the air in the space subjecting space boundaries andpatches to high cyclic loading Even small swells when confined can dislodge sturdy patches especially those fitted externally Patches ondeck openings may be struck and damaged by the rising water surface

A partially sunken ship on an exposed coast can be severely battered A sunken ship may retain sufficient buoyancy for one end to float whilethe other end rests on the bottom In this condition the casualty is moved about easily by wind and seas loss of buoyancy because of progressive flooding or venting of trapped air may allow the floating end to sink endangering nearby personnel and craft

6-324 Current Current forces push and rotate sunken ships The effective center of pressure of current force may be high enough to causea heeling moment Paragraph 3-451 describes the calculation of the force exerted by a current against a sunken shiprsquos hull To find the depthcorrection factor (K) from Figure 3-13 total height of the immersed ship should be substituted for draft in the water depth to draft ratio (d T )

If water depths and degree of immersion vary along the length of the casualty total current force can be calculated with a value for K based

on average d T ratio or by numerical integration If there is a significant vertical current gradient it is necessary to integrate vertically as wellas horizontally to determine the center of pressure for heeling moment calculations

Varying currents coupled with other effects may cause instability as the casualty is raised Current drag on the casualty tends to move bothit and any attached lifting vessels laterally Current intensity and direction may vary with depth When current direction varies with depthcurrent force vectors on the suspended vessel and the lift craft may come from different directions resulting in increased lift force When liftinga sunken vessel clear of the bottom enough tugs and moorings must be available to control the ship in the maximum current expected duringthe lift When the vessel is moved to a new site moors must be ready to receive her and be capable of holding her securely in the conditionsprevalent at that site

Current is a major factor limiting diver work Divers should be given priority use of slack water periods

6-4



S0300-A8-HBK-010

6-4 STABILITY OF SUNKEN SHIPS

Sunken ships are grouped into four categories by stability characteristics

bull Completely submerged

bull Partially submerged with a substantial portion of the watertight envelope above the surface

bull Partially supported by their buoyancy

bull Dewatered with cofferdams

Sunken ships refloat before all of the buoyancy lost in sinking has been recovered Water remaining on board can cause dangerous free surfac

and problems with stability list and local and overall hull strength Salvage of a sunken ship requires not only recovering enough buoyanc

to refloat the ship but also distributing buoyancy to obtain suitable conditions of stability trim and strength

Capsized ships are sometimes refloated upside down This technique is particularly suitable when the

bull Ship is capsized to more than 90 degrees

bull Shiprsquos bottom is relatively intact or can easily be made airtight

bull The ship is sunk in deep water or top hamper superstructure and other objects that increase the navigational draft of the inverte

ship can be removed easily

bull Channel to the ultimate destination is sufficiently deep to accommodate the inverted ship

bull Ship is to be sunk in deep water or scrapped

Capsized ships have been refloated successfully on their sides or upside down Experience has shown that ships floated upside down are usuall

quite stable when raised to a freeboard roughly equivalent to or only slightly greater than the height of the double bottom Similarly ful

bodied ships refloated at heel angles of 130 to 150 degrees with the turn of the bilge a few feet out of the water are generally quite stable

6-41 Completely Submerged Vessels Completely submerged vessels have no metacentric radius because there is no waterplane I WP an

consequently BM is zero Both transverse and longitudinal stability depend solely on the relative positions of the centers of buoyancy and grav

ity A submerged vessel free of external

Figure 6-1 Stability of Completely Sunken Ship

SHIP UPRIGHT CLEAR OF BOTTOMB IS ABOVE G - SHIP IS STABLE

G IS ABOVE B SHIP IS UNSTABLE

G

B

W WL L

UPSETTING MOMENT

G

B

restraints assumes trim and list that bring

the centers of buoyancy and gravity into

vertical line Stability of a completely sub-

merged ship is not a concern while the ship

is restrained from capsizing by the seafloor

However it is of major concern between

the time the ship leaves the bottom and

when it establishes positive stability on the

surface

The vertical separation of the centers of gravity and buoyancy ( BG) after

accounting for the effects of free surfaceis the measure of stability for a sunkenship As shown in Figure 6-1 if

bull B is above G the ship isstable

bull B and G coincide the ship has neutral stability

bull G is above B the ship is unstable

6-



S0300-A8-HBK-010

6-411 Free Surface in Submerged Vessels Free surface reduces righting arm in submerged vessels in the same manner as in surface vesselsThe opposing shifts of liquid and air can be considered to cause a shift in the center of gravity (added weight method) or center of buoyancy(lost buoyancy method)

In the added weight method of calculations reduction in righting arms is calculated by determining an equivalent rise of the center of gravity

GG1

=i

nabla

BGeff

= BG GG1

where

BGeff = effective (virtual) separation of the centers of buoyancy and gravity after accounting for free surface effecti = moment of inertia of the liquid surface in the compartmentnabla = volume of displacement of the vesselGG1 = vertical distance from the old center of gravity G to the new center of gravity G1

When a large free surface is in

Figure 6-2 Submerged Ship With Large Free Surface

W WL L

F

H1F1

H

FF2

B0

F1 E

H

S

H1

M1

D1D

O

OrsquoRN

NK K

(a) WITHOUT LONGITUDINAL SUBDIVISION (b) WITH LONGITUDINAL SUBDIVISION

G θ

B0

O

B1

M0

communication with the sea as whencapsized ships are raised with compressedair the lost buoyancy method of calculationsometimes gives a more enlighteningpicture of submerged vessel stability Thefree surface is the lower boundary of theshiprsquos intact buoyancy For cargo shipsfloated upside down without hatch coversor ships with large hull openings the freesurface can be viewed as an internalwaterline For a ship either upright orcapsized to 180 degrees the internalwaterline is perpendicular to thecenterplane If the ship is heeled as shownin Figure 6-2(a) the internal waterline (freesurface) is no longer perpendicular to the centerplane A wedge of buoyancy ( HOH 1) is transferred from one side of the ship to the other (FOF 1)causing an attendant shift of the center of buoyancy from B0 to B1 For the ship shown the centers of buoyancy and gravity are located so thatthe opposing forces of weight and buoyancy form an upsetting couplemdashthe ship is initially unstable A submerged metacenter (M 0) can bedefined in terms of the initial waterline FH and center of buoyancy B0

where I 0 is the moment of inertia of the internal waterplane FH (free surface) and nabla is the volume of displacement (buoyancy) If the center

B0 M

0=

I 0

nabla

of gravity lies below the metacenter the line of action of the downward force of buoyancy will be outboard the line of action of the upwardforce of buoyancy for small angles of heel creating a righting couple

A longitudinal bulkhead NN as shown in Figure 6-2(b) prevents the formation of the buoyancy wedges HOH 1 and FOF 1 Instead wedges of buoyancy are transferred within the compartments formed by the bulkhead ( DED1 to FEF 2 SOprime H to DOprime R) Metacentric radius is no longerbased on I 0 the moment of inertia of the waterplane FH but on the sum of the moments of inertia of the component surfaces FD and DH If the surface FD is small compared to FH then O and Oprime can be assumed to correspond and the combined moment of inertia can be approximatedby

where A is the area of the surface FD and d is the distance from the center of area FD to the shiprsquos centerplane ( EO) If longitudinal subdivision

I = I 0

Ad 2

is symmetric about the centerline O and Oprime correspond and the sum of the moment of inertia of the component surfaces can be closelyapproximated by deducting Ad 2 for all the component surfaces except the center surface from I 0

If the internal waterline FH corresponds to a watertight deck or bulkhead ie the compartment is completely dewatered and there is no freesurface there is no transfer of buoyancy from one side of the ship to the other with heel the center of buoyancy does not move The ship isstable so long as the center of gravity lies below the center of buoyancy

6-6



S0300-A8-HBK-010

6-412 Transition from Submerged to

Figure 6-3 Refloated Ship With Low Freeboard and Extensive Free Surface

HW L

F

L

L1

S1

B2

O

B3B1 B0

F1

M1

M0

M2

S

H1

Surfaced Stability As the ship begins tosurface and develop a waterplane ametacentric radius is formed and surface(form) stability becomes applicable Themetacentric radius is quite small at first themetacentric height often is negative and theship unstablemdashespecially if there is

appreciable free surface

A partially submerged ship with a largefree surface has both external and internalwaterlines as shown in Figure 6-3 Thevolume between the external and internalwaterlines represented in the figure byFF 1 LL1 is approximately equal to thevolume of displacement (nabla) As the shipinclines the external waterline becomes

HH 1 and the internal waterline becomesSS1 Since both the external and internalwaterplanes change as the ship inclines

Figure 6-4 Development of Stability in Raising a Completely Sunken Ship

SHIP COMPLETELYSUBMERGED

SHIP HAS NO WATERPLANEOR METACENTRICRADIUS B IS BELOW GSHIP IS UNSTABLE

PART OF SHIP EMERGESAND FORMS WATERPLANE

SUBMERGED VOLUME ISSTILL VERY LARGEMETACENTRIC RADIUSIS SMALL METACENTRICHEIGHT IS NEGATIVE

SHIP RAISED FURTHERSUBMERGED VOLUMEDECREASES

METACENTRIC RADIUSINCREASES METACENTRICHEIGHT BECOMES POSITIVESHIP BECOMES STABLE

G

B

(a) (b) (c)

MG

B

W L

M

G

B

both a surface stability metacenter (M 1) anda submerged metacenter (M 0) can be

defined M 1 is defined in the usual mannerby the waterplane FF 1

M 0 is similarly defined by the internal

B0 M

1=

I FF

1

nabla

waterplane LL1

It can be seen from Figure 6-3 that the

B0 M

0=

I LL

1

nabla

wedge of buoyancy at the external water-line is transferred from the high side to thelow side shifting B0 to B1 while at theinternal waterline the wedge is transferredfrom the low side to the high side shifting B0 to B2 The effects of the transference of buoyancy at the two waterlines tend to cancel leavinthe center of buoyancy at B3 The effective metacenter (M 2) is determined by the final position of the center of buoyancy (B3) The governinmetacentric radius can be defined in terms of the initial center of buoyancy (B0)

To be stable the shiprsquos center of gravity must lie below M 2

B0 M

2= B

0 M

0B

0 M

1

As the ship is raised further out of the water the external waterplane area increases with an attendant increase in moment of inertia while thvolume of displacement decreases simultaneously increasing B0 M 1 If the free surface (internal waterline) is eliminated B0 M 0 becomes zeroand B0 M 2 = - B0 M 1 ie M 1 and M 2 coincide and surface (form) stability considerations apply The period between the time the ship begins t

develop a waterplane and the time it attains positive form stability is critical During this period the ship must be stabilized to prevent capsizingFigure 6-4 illustrates the stability of a ship being raised from a completely submerged condition Sunken ships are seldom if ever raised withourestraint

Ships floated keel up should not be raised high out of the water especially when a large free surface exists As can be seen from Figure 6-3a waterline slightly below the double bottom will maximize the area and moment of inertia of the external waterplane On the other hand littlreduction in the area of the internal waterline will occur until the compartment(s) are virtually emptied Increasing freeboard will lower thcenter of buoyancy relative to the center of gravity without reducing free surface and very likely lead to an unstable condition

6-



S0300-A8-HBK-010

6-413 Attitude When Freely Floating A sunken shiprsquos center of buoyancy cannot be assumed to lie directly above the center of gravityThere is nearly always some longitudinal separation The salvage engineer must determine how much vertical lift force must be applied andhow it should be distributed to bring the

Figure 6-5 Submerged Equilibrium Attitude

α

B

αBGV

BGL

G

B G

B

G

centers of buoyancy and gravity into avertical line

Buoyancy of a sunken and flooded hullconsists of pockets of buoyancy distributed

throughout the ship The center of buoyancy is not simply the center of theenclosed volume of the ship but is derivedby dividing the sum of individual buoyancymoments by the total buoyancy in the sameway that the center of gravity is calculatedExternal lifting forces are treated as verticalforces applied where lift wires or slings areattached With the centers of buoyancy andgravity located the attitude of the vesselwhen clear of the bottom can be calculatedby simple geometry as shown in Figure 6-5

where

α = tan 1BG

L

BGV

θ = tan 1BG

T

BGV

α = angle of trimθ = angle ofheel

BG L = longitudinal separation of centers of buoyancy andgravity

BGV = vertical separation of centers of buoyancy and gravity

BGT = transverse separation of centers of buoyancy and gravity

To determine a submerged vesselrsquos response to external forces a righting arm (GZ ) curve can be constructed with the relationship

GZ = BGV tan θ

The same relationship is used to construct longitudinal and transverse stability curves If there is free surface effective or virtual BG is usedto develop the stability curves

In wholly submerged ships (no waterplane) effective longitudinal BG is nearly always less than effective transverse BG because tanks andcompartments in most ships are longer than they are wide and have greater moments of inertia about a transverse rather than longitudinal axisFree surface is more detrimental to longitudinal stability than to transverse stability

Sunken ships are normally raised from depths less than their length Longitudinal inclinations are therefore limited by the low end of the shipstriking bottom the high end reaching the surface or both The ship is supported partially by its buoyancy and partially by the ground asdescribed in Paragraph 6-43

The maximum longitudinal inclination a rising ship can attain is limited by the ratio of water depth to length

sinα asymp D

L

where

L = shiprsquos length D = water depthα = angle of inclination

Longitudinal inclination (trim angle) should be kept to less than 15 degrees

6-8



S0300-A8-HBK-010

6-42 Partially Submerged Vessels If

Figure 6-6 Sunken Ship Stability Main Deck Above Water

b

l

l

MBG

b

ONLY THE PORTION OF THE WATERPLANE ABOVE THE WATER-THE SHADED SECTION- CONTRIBUTES TO THE METACENTRIC RADIUS

W

W

L

L

the ship lies with part of her watertightvolume above the surface a metacentricradius can be calculated from the momentof inertia of the partial waterplaneBecause of the relatively small moment of inertia of the waterplane and the largeunderwater volume the metacentric radius

may be quite small Depending on thelocation of the center of gravity and extentof free surface the metacentric height maybe positive negative ormdashrarelymdashzero

As buoyancy is restored the externalwaterplane area increases causing themoment of inertia to increase The under-water volume decreases simultaneouslyThe overall result is that the metacentricradius increases and the ship becomespotentially more stable The overallstability of the ship depends upon theposition of the center of gravity and thefree surface in partially flooded spaces

Figure 6-6 illustrates the stability of a shipbeing raised with the main deck initiallypartially above water

If the bulk of the main deck is above thesurface there is a substantial waterplaneand the metacentric radius ( BM ) andmetacentric height (GM ) can be calculatedor estimated Normally G lies above Band ordinary stability considerationspertain

If B lies above G the ship is stable asshown in Figure 6-7 If the ship isrefloated by restoring buoyancy the centerof buoyancy moves down in the hull

crosses the position of the center of gravity


AS BUOYANCY IS RESTORED

B MOVES DOWN

G REMAINS AT THE SAME POSITION

I REMAINS THE SAME

V DECREASES

BM = ( I _ V

) INCREASES

G

K

B 1

M

G

K

B

M

W L W L

and eventually reaches a position B1 Asthe ship refloats BM increases because themoment of inertia of the waterplane ( I T )remains approximately constant as draftdecreases while the displacement volume(nabla) decreases Until B moves below Gstability is a function of the distance BGthe metacenter has no significance If apositive metacentric height is developed bythe time the center of buoyancy crosses theposition of the center of gravity the shipremains positively stable throughout therefloating However if there is zero ornegative metacentric height at the time B

reaches G the ship loses her stability anddevelops a list If there is a small positiveGM the effective GM may be negativewhen corrected for the free surface thatalways exists as the ship is dewatered If the ship was unstable in her afloatcondition she will be unstable as she isrefloated unless the conditions causing herinstability have been corrected Addition of high weight or removal of low weight during the salvage operation can cause an unstable afloacondition Far more common is a loss of stability caused by free surface It is possible that the free surface effect will be so great that the shicannot be stabilized by shifting internal weights When this occurs the ship must be stabilized by use of external forces The US Navy Shi

Salvage Manual Volume 2 (S0300-A6-MAN-020) discusses methods for stabilizing sunken ships during refloating

6-



S0300-A8-HBK-010

6-43 Ships Partially Supported by Their

FLOODED SPACES F PEAK

A PEAK

W L

ER4 DTK5

123

Figure 6-8 Sunken Ship Partially Supported by Buoyancy

Buoyancy A ship can sink so that one end

lies in contact with the ground and the

other end remains afloat as shown in

Figure 6-8 Although unlikely it is also

possible for a ship to be completely sub-

merged with one end off the ground sup-

ported by buoyancy as shown in Figure 6-

9 As in the case of a stranded ship the

sum of ground reaction and buoyancy must

equal the total weight of the ship By the

added weight method a shiprsquos total

buoyancy is the volume of its immersed

portion plus the volume of all topside ap-

pendages multiplied by water density The

total weight is the presinking displacement

plus the weight of floodwater By the lost

Figure 6-9 Ground Reaction for Partially Buoyant (Submerged) Ship

B

RWRGHBGH

B

G

W L

buoyancy method weight remains equal to

the presinking displacement while

buoyancy is proportional to the volume of

immersed structure cargo stores etc The

amount of buoyancy lost is therefore equal

to the weight of floodwater If permeability of the flooded spaces is known

or can be estimated weight of floodwater

can be calculated as described in Chapter 1

The volume of immersed topside ap-

pendages adds some buoyancy By sum-

ming moments about the center of gravity

as shown in Figure 6-9 ground reaction at

the equilibrium inclination can be

determined

B BG H

= R RG H

R = B BG

H

RG H

where

B = total buoyancy

BG H = horizontal separation between B and G

= ( LCG - LCB)sinα R = ground reaction

RG H = horizontal separation between R and G

asymp LCGsinα (aground at the bow)

asymp ( L - LCG)sinα (aground at the stern)

α = angle of inclination

The relationship is simple but centers of gravity and buoyancy may be difficult to determine accurately

A ship supported partially by its buoyancy is in a precarious situation Loss of additional buoyancy by progressive flooding or damage can cause

the ship to sink completely sometimes rapidly and with little warning Intact spaces must be examined thoroughly and secured against

progressive flooding early in the salvage operation A ship partially afloat is affected by current wind and waves Lateral forces tend to cause

both translation and rotation around the grounded end Because current strength and direction both may vary with depth the resultant current

force is the vector sum of current forces at different levels

Trapped air can hold a completely submerged casualty at an angle of list If the air vents the casualty may settle into either an upright or

capsized position A sunken ship protruding over the edge of a reef or ridge may be partially supported by her buoyancy Loss of buoyancy

may cause the casualty to drop over the edge into deeper water A sunken ship in a potentially unstable position can be stabilized by taking

an upward strain on the vessel with pontoons lift craft or sheer legs capable of holding the vessel in position The floating end of a partially

sunken vessel might be held up with pontoons or lift craft made up alongside In some cases it may be necessary to vent trapped air from the

casualty to allow it to settle to a stable position at the expense of incurring extra work to raise it from that position

6-10



S0300-A8-HBK-010

6-44 Ships Dewatered with Cofferdams A ship with main deck submerged that is raised by dewatering with a complete cofferdam exhibitstability characteristics similar to those of a ship with main deck initially above the water The waterplane area and moment of inertia of thcofferdam are nearly as large as those of the hull although the displacement volume is much larger from the time the ship leaves the bottomuntil it is floating at a normal draft The cofferdam is a large high weight that raises the center of gravity and reduces metacentric heighConstruction and application of salvage cofferdams are discussed in the US Navy Salvage Manual Volume 2 (S0300-A6-MAN-020)

A ship raised by dewatering through partial cofferdams is similar to a ship with a partial waterplane As the ship begins to float metacentriradius is determined initially by the relatively small waterplane of the cofferdams The plan area of partial cofferdams is usually smaller tha

that of the spaces over which they are placed When the internal water level has been pumped down past the main deck the free surface areis larger than the waterplane area The free surface is almost always at least as wide as the cofferdam and usually is wider Thus the momenof inertia of the free surface (i) is greater than that of the waterplane ( I ) and metacentric height is negative

BM =I

nabla

BM eff

=I

nablaFS =

I

nablai

nabla=

I i

nabla

since i is greater than I BM eff is negative and unless KG is greater than KB GM eff is also negative

If there is free communication within the hull so that the water level falls simultaneously in several compartments free surface effect may bemuch larger than metacentric height

As the main deck breaks the water surface waterplane area increases and depending on the relative sizes of the waterplane and free surfacmoments of inertia GM may either become positive or remain negative until free surface is suppressed by dewatering

6-45 Buoyancy and Free Surface Sunken ships are raised by one of three methods

bull Internal (buoyant) lift

bull External lift

bull Combined internal and external lift

How and where the buoyant and lift forces are applied affect stability of the casualty Buoyant forces can be grouped into four types baseon their effects on stability

bull Fixed buoyancy without free surface

bull Fixed buoyancy with free surface

bull Variable buoyancy with free surface

bull Variable buoyancy without free surface

Each type of buoyancy behaves differently as the ship ascends

6-451 Fixed Buoyancy without Free Surface Fixed buoyancy without free surface can be provided by

bull Compartments vented at the bottom and blown dry by compressed air

bull Completely dry tanks or spaces capable of withstanding ambient pressure such as submarine hard tanks

bull Blocks of buoyant solid such as cast-in-place foam or buoyant cargo held firmly in place

bull Lifting forces from submerged lift bags pontoons etc

Buoyancy remains constant and stationary relative to the ship Center of buoyancy and total buoyancy remain unchanged as the ship ascendsPontoons rigged above a casualty on lifting pendants provide constant buoyancy until they reach the surface where the volume of the emergeportions of the pontoon no longer provides buoyancy Pontoons are often rigged this way to arrest the ascent of the ship or object being raiseat a specified depth

6-452 Fixed Buoyancy with Free Surface Fixed buoyancy with free surface exists in partially dewatered compartments not exposed toambient pressure eg submarine internal compartments The buoyancy of loose masses of objects that can be considered incompressible sucas rigid buoys floats and some types of cargo remains constant as the ship ascends Unless the objects completely fill the space a free surfacexists and the center of buoyancy can shift as the objects move to one side or to the end of the space

6-1



S0300-A8-HBK-010

As soon as the ship leaves the bottom the buoyancy in each compartment shifts causing the center of buoyancy to move This is the equivalentof the free surface effect in surface stability The effect of free surface on stability of a sunken ship is discussed in Paragraph 6-41

6-453 Variable Buoyancy with Free Surface Compressed air in a shiprsquos hull expands while hydrostatic pressure decreases as the ship risesAir in partially dewatered compartments exposed to ambient pressure partially filled lift bags or any other space where the water level is abovethe vent opening expands as the ship rises In addition to the free surface effects discussed above buoyancy increases rapidly as the ship risescausing rapid and probably uncontrolled ascent A ship raised from a shallow depth will be on the surface before it can assume an extreme trimA ship raised from a significant depth may develop extreme trim which can cause air to spill from vent holes low in air-filled compartments

If this happens buoyancy is lost as the compartments flood and the ship may sink again The casualty may be damaged in its second sinkingTopside rigging can be overstressed and parted by the sudden weight increase as the casualty floods or by the uneven loads caused by extremetrim In addition subsurface rigging can become hopelessly tangled

6-454 Variable Buoyancy without Free Surface Lift craft and surface pontoons can be rigged to provide a submerged vessel a form of reserve buoyancy and waterplane If slings are made up to solid attachment points on opposite sides (or ends) of the sunken vessel inclinationincreases tension on slings on one side If the slings are made up to pontoons or lift craft on the surface the lift craft sinks to gain buoyancyequivalent to the increased tension and restore equilibrium

6-46 Longitudinal Stability Because of the effect of length on a waterplanersquos moment of inertia ships with any significant length of waterplane are inherently longitudinally stable In ships with limited or no internal transverse subdivision free surface may overcomelongitudinal stability while the ship is being raised It is impractical to keep a ship perfectly horizontal while it is raised free water shifts tothe low end causing trimming moments Because the ship trims as the water shifts large trim angles can be reached before the mass of waterreaches the low end The mass of water rushing to the low end of compartments can have enough momentum to cause significant impact loadson patches and internal structures Impact loads and extreme trim can have several detrimental effects

bull Downflooding can occur through topside openings or over the tops of cofferdams with subsequent loss of buoyancy and plunging

bull The casualty may rise out of lifting slings on one end and overload and part slings at the other end

bull Impact loads can damage patches internal structure or shell plating

bull Impact forces may be transmitted to lifting slings overloading them

bull Impact forces on bulkheads and shell plating can cause longitudinal surging while downward components momentarily increase

trimming moment causing pitching Uncontrolled motions can allow the casualty to slip out of lifting slings or to overload them

A ship with no waterplane has only the longitudinal righting moment provided by the relative positions of the centers of gravity and buoyancyThe ship must be raised without trim or must be kept in contact with the bottom as she is moved into water shallow enough for a waterplaneand adequate longitudinal metacentric radius to develop

6-47 Keeping the Ship Upright As the ship is raised various methods can prevent capsizing while it passes through unstable phases

bull Refloating one end of the vessel while keeping the other end firmly in contact with the bottom Compartments in the raised end

can be dried out completely topside weight removed or double-bottom tanks flooded to improve stability before raising the otherend

bull Keeping the vessel in contact with the bottom by pulling it into shallower water as it is raised

bull Keeping full-bodied vessels in water shallow enough that the bilge strikes bottom and prevents the ship from capsizing

bull Dewatering holds or major subdivisions one at a time to limit free surface

bull Breaking up large free surfaces by repairing damaged bulkheads and building temporary bulkheads in the flooded spaces

bull Applying external forces to produce righting moments that counter upsetting moments

(1) Lifting on the deck edges with sheer legs or cranes to prevent excessive list

(2) Holding the vessel upright by tensioning a line led from a mast or kingpost to a deadman

bull Rigging barges pontoons or lift craft tightly alongside to provide added buoyancy and waterplane

It is not always advisable to bring a sunken ship directly to the surface particularly from great depths A single long lift involves greaterpressure changes of air in the casualty and pontoons with greater possibility of losing control Hydrodynamic drag or currents can causeinstability as the casualty rises through the water column While a casualty is submerged work on it must be performed by divers whose ef-fectiveness is reduced with depth These factors may dictate raising the casualty in a series of short lifts and moving it to shallower water aftereach lift to re-rig for the next one With the casualty resting in shallower water divers can make preparations for raising it to the surface withgreater efficiency and safety It may be advisable to keep some cargoes or munitions submerged until specialized facilities for handling andreceiving them are available The US Navy Ship Salvage Manual Volume 2 (S0300-A6-MAN-020) discusses these methods in greater detail

6-12



S0300-A8-HBK-010

6-5 STRENGTH OF SUNKEN SHIPS

Local longitudinal bending and shear strength of sunken ships are often impaired by the damage that led to their sinking The strength of thsunken ship can have a major influence on the salvage methods selected

Bending and shear stresses in sunken ships are determined by the same methods used for intact ships These methods are described in Paragrap1-11 If an evaluation of the longitudinal and shear strength reveals adequate strength the salvage may proceed There must be an adequat

margin of strength at each stage of the salvage to allow for unknown conditions

If the survey or initial strength evaluation shows that the hull girder has failed or that failure is probable during the salvage the hull must bereinforced or extraordinary measures must be adopted to prevent catastrophic failure and to allow completion of the operation Even in shipdestined for disposal structural failure must be prevented as it may occur at the worst possible time and may create a situation worse than thinitial sinking

When the hull girder has failed or can be expected to fail during salvage the hull may be reinforced by providing additional material in wayof incipient failure to restore the section modulus or increase the shear area Structural reinforcement and repair are addressed in Paragrap2-11

In cases where there is massive failure of the hull and it is impractical to restore any hull strength zero-shearzero-stress methods arappropriate These methods load the hull so that zero shear or zero bending moment occurs at the point where the hull has failed and plastihinges have formed They require the parts of the ship between hinges or badly damaged sections to be treated as independent hulls couplewith rigorous and accurate weight and buoyancy analysis to determine proper loading

6-6 RIGHTING CAPSIZED SHIPS

When ships are capsized their salvage or removal usually requires a detailed engineering analysis and plan Most capsized ships are rightefirst and then raised In this approach the work is done in two distinct phases The first phase brings the ship upright then the second raiseher like any other upright sunken ship When righting and refloating are done by stages refloating work may start as soon as the ship isufficiently upright that men can work aboard her

Ships are righted by creating a moment with buoyancy or externally applied force that acts around a pivot point to overcome the moment ofweight acting through the center of gravity holding the ship in a capsized position

When a ship is being righted the ground under the pivot point must have enough bearing strength to support the ship during the rightingoperation If the ground is too soft the ship may either sink into or slide along the bottom inhibiting the righting process

During rotation if only the pivoting axis (usually the bilge) is in contact with the ground bearing pressure ( P B) equals the bearing force (F Bdivided by the minimum contact area ( A)

P B

=F

B

A

If the casualty is being righted by internal buoyancy moments the bearing force is the ground reaction and is equal to the total weight less thtotal buoyancy of the casualty

F B = W - B

If externally applied forces generate righting moments the bearing force is the total weight of the casualty less the buoyancy plus the downwardcomponent of the righting forces (F Rz)

F B = W - B + F Rz

Bearing force must be calculated using the minimum buoyancy that exists as the vessel is rotated

Soil bearing strength is determined by the methods described in Paragraph 3-7 Table 3-6 gives approximate bearing strengths for different typeof soil If the ground under the ship is not sufficiently firm it may be stabilized by laying in gravel crushed rock or coral or shell

6-13 (6-14 blank



S0300-A8-HBK-010

Sinking often results from flooding following hull damage additional damage may result when the ship strikes or settles on the bottom A diving

survey can provide an accurate picture of the shiprsquos condition but indications of some conditions may be visible from the surface If the

casualtyrsquos masts either converge or diverge the ship may have broken in sinking If one end of a ship sank rapidly while the other end remained

afloat for several hours it is likely that little or no damage occurred to the slowly sinking end and that the vessel lost buoyancy through slow

seepage Differences between water levels inside and outside of a partially sunken ship and between compartments within the ship (as the tide

rises or falls) may indicate the extent of damage to shell and bulkheads

6-3 ENVIRONMENTAL EFFECTS

Environmental effects on sunken ships include responses of the seafloor to loading by the casualty and fluid forces of the surrounding water

In a sinking much of the casualty is exposed to hydrostatic pressure current forces and current-induced scour or silting Work on the casualty

must be accomplished through the water column Wind and weather affect salvors and salvage vessels alike

6-31 Seafloor Effects Effects of the seafloor on a sunken casualty include

bull Gradual sinkage into the seafloor

bull Suction on cohesive seafloors

bull Hull girder stresses caused by uneven support

bull Obstructions presented by the bottom topography

bull Scour

bull Silting

Composition and consistency of the seafloor under the ship and slope of the seafloor near the casualty are the two most important characteristics

influencing seafloor effects The US Navy Ship Salvage Manual Volume 2 (S0300-A6-MAN-020) discusses the general effects of the seafloor

on sunken vessels and lifting operations Paragraph3-73 describes calculation of bottom breakout forces required to break seafloor suction

Silt and mud that settle in the ship constitute weight that must be either removed or overcome during the refloating Removing silt and mud

lightens the ship and makes her behavior more predictable Chapter 5 discusses the use of air lifts and other underwater excavation methods suit-

able for removing accumulated silt from sunken ships The weight of mud varies with the type of soil Table 3-3 lists some typical values for

underwater weightmdashthe weight of the soil less the weight of the displaced water Because of internal voids one cubic foot of soil displaces less

than one cubic foot of water The actual volume of water displaced by a volume of soil depends on the compactness or porosity (ratio of volume

of voids to volume of soil particles) of the soil Porosity ranges from 03 for dense settled sand to 06 for recently deposited loose silt

Mud removed from a casualty is sometimes deposited on a barge or ashore The weight of spoil can be estimated from the change in barge

draft This weight is greater than the weight removed from the casualty because it includes weight of water trapped in the soil The weight

removed can be estimated by multiplying spoil weight by the solidrsquos proportion (1 minus porosity) Wet weight can be determined simply by

weighing a bucket of mud brought up from the wreck if time permits the weight of solids for a given volume of mud can be determined by

drying the mud before weighing A microwave oven is convenient for drying soil samples

6-32 Fluid Forces Fluid forces on a sunken ship derive from the depth of water in which the ship lies and the effects of tide waves swell

and current

6-321 Water Depth Because hydrostatic pressure increases with depth water depth determines the hydrostatic pressures on the casualty bothas it sits and as it is raised The fact that pressure complicates the salvage of sunken ships is a major reason why deeply sunken ships are seldom

salvaged Pressure varies with depth according to the following relationship

ph = γ wd

where

ph = hydrostatic pressure

γ = weight density of water = ρggc (seeParagraphD-41)

d = water depth

6-2



S0300-A8-HBK-010




Type GradePlate

Thicknessin

Deck CutOverall

Size in

CoverOverall

Size in

Numberof Bolts

or Studs

DesignPressure

psi








in


in


Number ofBolts or

Studs

DesignPressure

psi








Type GradePlate

Thicknessin

Deck CutOverall

Size in

CoverOverall

Size in


DesignPressure

psi








where

ph

=

γ 144

d

= 0445d (seawater)














of seawater)






6-



S0300-A8-HBK-010


















6-4



S0300-A8-HBK-010


























G

B

W WL L

UPSETTING MOMENT

G

B









surface






6-



S0300-A8-HBK-010



GG1

=i

nabla

BGeff

= BG GG1

where




W WL L

F

H1F1

H

FF2

B0

F1 E

H

S

H1

M1

D1D

O

OrsquoRN

NK K


G θ

B0

O

B1

M0



B0 M

0=

I 0

nabla




I = I 0

Ad 2



6-6



S0300-A8-HBK-010



HW L

F

L

L1

S1

B2

O

B3B1 B0

F1

M1

M0

M2

S

H1












G

B

(a) (b) (c)

MG

B

W L

M

G

B




B0 M

1=

I FF

1

nabla

waterplane LL1


B0 M

0=

I LL

1

nabla



B0 M

2= B

0 M

0B

0 M

1




6-



S0300-A8-HBK-010



α

B

αBGV

BGL

G

B G

B

G




where

α = tan 1BG

L

BGV

θ = tan 1BG

T

BGV






GZ = BGV tan θ





sinα asymp D

L

where



6-8



S0300-A8-HBK-010



b

l

l

MBG

b


W

W

L

L










B MOVES DOWN


I REMAINS THE SAME

V DECREASES

BM = ( I _ V

) INCREASES

G

K

B 1

M

G

K

B

M

W L W L




6-



S0300-A8-HBK-010



A PEAK

W L

ER4 DTK5

123



















B

RWRGHBGH

B

G

W L














determined

B BG H

= R RG H

R = B BG

H

RG H

where

B = total buoyancy



















6-10



S0300-A8-HBK-010




BM =I

nabla

BM eff

=I

nablaFS =

I

nablai

nabla=

I i

nabla






bull External lift















6-1



S0300-A8-HBK-010

























6-12



S0300-A8-HBK-010













P B

=F

B

A


F B = W - B


F B = W - B + F Rz



6-13 (6-14 blank



S0300-A8-HBK-010




Type GradePlate

Thicknessin

Deck CutOverall

Size in

CoverOverall

Size in

Numberof Bolts

or Studs

DesignPressure

psi








in


in


Number ofBolts or

Studs

DesignPressure

psi








Type GradePlate

Thicknessin

Deck CutOverall

Size in

CoverOverall

Size in


DesignPressure

psi








where

ph

=

γ 144

d

= 0445d (seawater)














of seawater)






6-



S0300-A8-HBK-010


















6-4



S0300-A8-HBK-010


























G

B

W WL L

UPSETTING MOMENT

G

B









surface






6-



S0300-A8-HBK-010



GG1

=i

nabla

BGeff

= BG GG1

where




W WL L

F

H1F1

H

FF2

B0

F1 E

H

S

H1

M1

D1D

O

OrsquoRN

NK K


G θ

B0

O

B1

M0



B0 M

0=

I 0

nabla




I = I 0

Ad 2



6-6



S0300-A8-HBK-010



HW L

F

L

L1

S1

B2

O

B3B1 B0

F1

M1

M0

M2

S

H1












G

B

(a) (b) (c)

MG

B

W L

M

G

B




B0 M

1=

I FF

1

nabla

waterplane LL1


B0 M

0=

I LL

1

nabla



B0 M

2= B

0 M

0B

0 M

1




6-



S0300-A8-HBK-010



α

B

αBGV

BGL

G

B G

B

G




where

α = tan 1BG

L

BGV

θ = tan 1BG

T

BGV






GZ = BGV tan θ





sinα asymp D

L

where



6-8



S0300-A8-HBK-010



b

l

l

MBG

b


W

W

L

L










B MOVES DOWN


I REMAINS THE SAME

V DECREASES

BM = ( I _ V

) INCREASES

G

K

B 1

M

G

K

B

M

W L W L




6-



S0300-A8-HBK-010



A PEAK

W L

ER4 DTK5

123



















B

RWRGHBGH

B

G

W L














determined

B BG H

= R RG H

R = B BG

H

RG H

where

B = total buoyancy



















6-10



S0300-A8-HBK-010




BM =I

nabla

BM eff

=I

nablaFS =

I

nablai

nabla=

I i

nabla






bull External lift















6-1



S0300-A8-HBK-010

























6-12



S0300-A8-HBK-010













P B

=F

B

A


F B = W - B


F B = W - B + F Rz



6-13 (6-14 blank



S0300-A8-HBK-010


















6-4



S0300-A8-HBK-010


























G

B

W WL L

UPSETTING MOMENT

G

B









surface






6-



S0300-A8-HBK-010



GG1

=i

nabla

BGeff

= BG GG1

where




W WL L

F

H1F1

H

FF2

B0

F1 E

H

S

H1

M1

D1D

O

OrsquoRN

NK K


G θ

B0

O

B1

M0



B0 M

0=

I 0

nabla




I = I 0

Ad 2



6-6



S0300-A8-HBK-010



HW L

F

L

L1

S1

B2

O

B3B1 B0

F1

M1

M0

M2

S

H1












G

B

(a) (b) (c)

MG

B

W L

M

G

B




B0 M

1=

I FF

1

nabla

waterplane LL1


B0 M

0=

I LL

1

nabla



B0 M

2= B

0 M

0B

0 M

1




6-



S0300-A8-HBK-010



α

B

αBGV

BGL

G

B G

B

G




where

α = tan 1BG

L

BGV

θ = tan 1BG

T

BGV






GZ = BGV tan θ





sinα asymp D

L

where



6-8



S0300-A8-HBK-010



b

l

l

MBG

b


W

W

L

L










B MOVES DOWN


I REMAINS THE SAME

V DECREASES

BM = ( I _ V

) INCREASES

G

K

B 1

M

G

K

B

M

W L W L




6-



S0300-A8-HBK-010



A PEAK

W L

ER4 DTK5

123



















B

RWRGHBGH

B

G

W L














determined

B BG H

= R RG H

R = B BG

H

RG H

where

B = total buoyancy



















6-10



S0300-A8-HBK-010




BM =I

nabla

BM eff

=I

nablaFS =

I

nablai

nabla=

I i

nabla






bull External lift















6-1



S0300-A8-HBK-010

























6-12



S0300-A8-HBK-010













P B

=F

B

A


F B = W - B


F B = W - B + F Rz



6-13 (6-14 blank



S0300-A8-HBK-010


























G

B

W WL L

UPSETTING MOMENT

G

B









surface






6-



S0300-A8-HBK-010



GG1

=i

nabla

BGeff

= BG GG1

where




W WL L

F

H1F1

H

FF2

B0

F1 E

H

S

H1

M1

D1D

O

OrsquoRN

NK K


G θ

B0

O

B1

M0



B0 M

0=

I 0

nabla




I = I 0

Ad 2



6-6



S0300-A8-HBK-010



HW L

F

L

L1

S1

B2

O

B3B1 B0

F1

M1

M0

M2

S

H1












G

B

(a) (b) (c)

MG

B

W L

M

G

B




B0 M

1=

I FF

1

nabla

waterplane LL1


B0 M

0=

I LL

1

nabla



B0 M

2= B

0 M

0B

0 M

1




6-



S0300-A8-HBK-010



α

B

αBGV

BGL

G

B G

B

G




where

α = tan 1BG

L

BGV

θ = tan 1BG

T

BGV






GZ = BGV tan θ





sinα asymp D

L

where



6-8



S0300-A8-HBK-010



b

l

l

MBG

b


W

W

L

L










B MOVES DOWN


I REMAINS THE SAME

V DECREASES

BM = ( I _ V

) INCREASES

G

K

B 1

M

G

K

B

M

W L W L




6-



S0300-A8-HBK-010



A PEAK

W L

ER4 DTK5

123



















B

RWRGHBGH

B

G

W L














determined

B BG H

= R RG H

R = B BG

H

RG H

where

B = total buoyancy



















6-10



S0300-A8-HBK-010




BM =I

nabla

BM eff

=I

nablaFS =

I

nablai

nabla=

I i

nabla






bull External lift















6-1



S0300-A8-HBK-010

























6-12



S0300-A8-HBK-010













P B

=F

B

A


F B = W - B


F B = W - B + F Rz



6-13 (6-14 blank



S0300-A8-HBK-010



GG1

=i

nabla

BGeff

= BG GG1

where




W WL L

F

H1F1

H

FF2

B0

F1 E

H

S

H1

M1

D1D

O

OrsquoRN

NK K


G θ

B0

O

B1

M0



B0 M

0=

I 0

nabla




I = I 0

Ad 2



6-6



S0300-A8-HBK-010



HW L

F

L

L1

S1

B2

O

B3B1 B0

F1

M1

M0

M2

S

H1












G

B

(a) (b) (c)

MG

B

W L

M

G

B




B0 M

1=

I FF

1

nabla

waterplane LL1


B0 M

0=

I LL

1

nabla



B0 M

2= B

0 M

0B

0 M

1




6-



S0300-A8-HBK-010



α

B

αBGV

BGL

G

B G

B

G




where

α = tan 1BG

L

BGV

θ = tan 1BG

T

BGV






GZ = BGV tan θ





sinα asymp D

L

where



6-8



S0300-A8-HBK-010



b

l

l

MBG

b


W

W

L

L










B MOVES DOWN


I REMAINS THE SAME

V DECREASES

BM = ( I _ V

) INCREASES

G

K

B 1

M

G

K

B

M

W L W L




6-



S0300-A8-HBK-010



A PEAK

W L

ER4 DTK5

123



















B

RWRGHBGH

B

G

W L














determined

B BG H

= R RG H

R = B BG

H

RG H

where

B = total buoyancy



















6-10



S0300-A8-HBK-010




BM =I

nabla

BM eff

=I

nablaFS =

I

nablai

nabla=

I i

nabla






bull External lift















6-1



S0300-A8-HBK-010

























6-12



S0300-A8-HBK-010













P B

=F

B

A


F B = W - B


F B = W - B + F Rz



6-13 (6-14 blank



S0300-A8-HBK-010



HW L

F

L

L1

S1

B2

O

B3B1 B0

F1

M1

M0

M2

S

H1












G

B

(a) (b) (c)

MG

B

W L

M

G

B




B0 M

1=

I FF

1

nabla

waterplane LL1


B0 M

0=

I LL

1

nabla



B0 M

2= B

0 M

0B

0 M

1




6-



S0300-A8-HBK-010



α

B

αBGV

BGL

G

B G

B

G




where

α = tan 1BG

L

BGV

θ = tan 1BG

T

BGV






GZ = BGV tan θ





sinα asymp D

L

where



6-8



S0300-A8-HBK-010



b

l

l

MBG

b


W

W

L

L










B MOVES DOWN


I REMAINS THE SAME

V DECREASES

BM = ( I _ V

) INCREASES

G

K

B 1

M

G

K

B

M

W L W L




6-



S0300-A8-HBK-010



A PEAK

W L

ER4 DTK5

123



















B

RWRGHBGH

B

G

W L














determined

B BG H

= R RG H

R = B BG

H

RG H

where

B = total buoyancy



















6-10



S0300-A8-HBK-010




BM =I

nabla

BM eff

=I

nablaFS =

I

nablai

nabla=

I i

nabla






bull External lift















6-1



S0300-A8-HBK-010

























6-12



S0300-A8-HBK-010













P B

=F

B

A


F B = W - B


F B = W - B + F Rz



6-13 (6-14 blank



S0300-A8-HBK-010



α

B

αBGV

BGL

G

B G

B

G




where

α = tan 1BG

L

BGV

θ = tan 1BG

T

BGV






GZ = BGV tan θ





sinα asymp D

L

where



6-8



S0300-A8-HBK-010



b

l

l

MBG

b


W

W

L

L










B MOVES DOWN


I REMAINS THE SAME

V DECREASES

BM = ( I _ V

) INCREASES

G

K

B 1

M

G

K

B

M

W L W L




6-



S0300-A8-HBK-010



A PEAK

W L

ER4 DTK5

123



















B

RWRGHBGH

B

G

W L














determined

B BG H

= R RG H

R = B BG

H

RG H

where

B = total buoyancy



















6-10



S0300-A8-HBK-010




BM =I

nabla

BM eff

=I

nablaFS =

I

nablai

nabla=

I i

nabla






bull External lift















6-1



S0300-A8-HBK-010

























6-12



S0300-A8-HBK-010













P B

=F

B

A


F B = W - B


F B = W - B + F Rz



6-13 (6-14 blank



S0300-A8-HBK-010



b

l

l

MBG

b


W

W

L

L










B MOVES DOWN


I REMAINS THE SAME

V DECREASES

BM = ( I _ V

) INCREASES

G

K

B 1

M

G

K

B

M

W L W L




6-



S0300-A8-HBK-010



A PEAK

W L

ER4 DTK5

123



















B

RWRGHBGH

B

G

W L














determined

B BG H

= R RG H

R = B BG

H

RG H

where

B = total buoyancy



















6-10



S0300-A8-HBK-010




BM =I

nabla

BM eff

=I

nablaFS =

I

nablai

nabla=

I i

nabla






bull External lift















6-1



S0300-A8-HBK-010

























6-12



S0300-A8-HBK-010













P B

=F

B

A


F B = W - B


F B = W - B + F Rz



6-13 (6-14 blank



S0300-A8-HBK-010



A PEAK

W L

ER4 DTK5

123



















B

RWRGHBGH

B

G

W L














determined

B BG H

= R RG H

R = B BG

H

RG H

where

B = total buoyancy



















6-10



S0300-A8-HBK-010




BM =I

nabla

BM eff

=I

nablaFS =

I

nablai

nabla=

I i

nabla






bull External lift















6-1



S0300-A8-HBK-010

























6-12



S0300-A8-HBK-010













P B

=F

B

A


F B = W - B


F B = W - B + F Rz



6-13 (6-14 blank



S0300-A8-HBK-010




BM =I

nabla

BM eff

=I

nablaFS =

I

nablai

nabla=

I i

nabla






bull External lift















6-1



S0300-A8-HBK-010

























6-12



S0300-A8-HBK-010













P B

=F

B

A


F B = W - B


F B = W - B + F Rz



6-13 (6-14 blank



S0300-A8-HBK-010

























6-12



S0300-A8-HBK-010













P B

=F

B

A


F B = W - B


F B = W - B + F Rz



6-13 (6-14 blank



S0300-A8-HBK-010













P B

=F

B

A


F B = W - B


F B = W - B + F Rz



6-13 (6-14 blank

Documents

Buques En Calla Dos y Volcados