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TMC (Marine Consultants) Ltd. Stability & Global Strength
Telephone: +44 (0)20 7237 2617, email: [email protected]
www.tmcmarine.co.uk
Ship Stability & Global Strength
SEAMASTER (Program Suite)
SEAMASTER was originally written in 1979 by the founding partners of TMC, and after
continuous upgrading over the years this hydrostatic program remains one of the core in-house
programs. The program is used for retrospective investigations on opinion work and also as a pro-
active tool during salvage consultancy. The program is also sold to clients as an onboard loading
instrument and has been installed on many vessels over the last 20 years.
TMC carry out intact and damaged stability and longitudinal strength analyses using their in-house,
hydrostatic program SEAMASTER, which has been class approved as a loading instrument on a
case by case basis for specific ships. The program performs stability and strength analyses,
calculated using trimmed hydrostatics.
Figure 1: SEAMASTER Program screen view showing vessel profile with stability and
longitudinal strength results. Stability criteria may be presented in terms of actual values (shown)
or conventional criteria requirements.
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TMC (Marine Consultants) Ltd. Stability & Global Strength
Telephone: +44 (0)20 7237 2617, email: [email protected]
www.tmcmarine.co.uk
Program Modules
TMCs own additional modules are integrated seamlessly within SEAMASTER depending on
vessel type and options required to be considered. The modules are listed below:
SEACOC cargo operation control which simulates any proposed loading/ballast sequenceand reports automatically on the stability and strength at all intermediate stages;
SEAFLOOD immediate access to the effect of flooding any combination of compartments; SEADAM investigates stresses in the hull, damaged or intact, including wave loading effects
and also the consequences of grounding;
C-PLAN a stowage planning tool which stores container details in database, automaticallystows containers, and allows the rapid assessment of loading options;
T-PLAN for planning the loading of tankers to be partially discharged at a number of portsand also generates Tanker Forms in accordance with commercial practice;
COMLASH analyses all container and lashing forces. This is an autonomous module, butmay be used in conjunction with C-PLAN, above (see separate download for COMLASH).
Data Required
The amount of plans (as-built and approved) and supporting documentation required depends on
the level of modelling complexity required, and also how comprehensive various sources of dataare. Accordingly, some or all of the following data will normally be required:
- Lines plan / body plan / offsets / other approximate source (e.g. docking plan);- General arrangement;- Capacity plan;- Profile and Decks plan;- Midship Section;- Shell expansion;- Stability book and longitudinal strength information (including comprehensive tabulated
hydrostatics, lightship weight distribution, standard loading conditions);
- Actual scantlings (e.g. thickness gauging report);- Loading condition;- Draught surveys;- Damage status report;- Sea wave data (for specific wave loads);
In cases where there is no data available, it is often possible to construct a model using an existing
model from our extensive library, as TMC has a database of some 400 models of various ship types
created using SEAMASTER, from which a geometrically similar, or even sister, ship may be
derived.
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TMC (Marine Consultants) Ltd. Stability & Global Strength
Telephone: +44 (0)20 7237 2617, email: [email protected]
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Modelling
Hull Form the SEAMASTER program initially requires a hull form to be generated which is
defined using transverse sections. Input data is required in the form of hull offset data obtained
from either lines plan, body plan or tabulated values (other sources such as docking plan are alsouseful). Plans can also be inputted manually, imported via spreadsheet or via digitiser. Shell plate
thickness can be attributed at the end in order to distinguish moulded and extreme dimensions.
Hull Appendages external appendages such as skeg, rudder, bar keel, etc and hull cut-outs (e.g.
tunnel thrusters) that influence buoyancy or which may be required for graphical or geometric
purposes can also be defined. The program has been proven by validation of hydrostatics with
published design data over the years, together with class approval procedures on a case-by-case
basis. Usage onboard as a loading instrument, as well as for salvage cases and for retrospective
analysis has confirmed the high degree of accuracy of the program in cases where the hull form and
internal compartment geometries are known.
Internal compartments - in most cases, internal spaces are required to be defined, either for
geometrical reasons alone or because of complex filling of bulk cargo/liquid and associated
permeability levels. Internal tanks and spaces are defined by boundaries comprising flat or
horizontal plane surfaces, or more complex polygons where boundaries are irregular, and in any
orientation.
Loading either by geometrical compartment loading (see above) or by non-geometrical point
loads which can, if required, be assigned a distributed length to simulate a uniformly distributed
load over the boundary defined. Also, a free surface moment of a non-geometrical point load can
be assigned. Calculated volumetric capacities and free surface moments may be validated against
vessel data, where available.
Figure 2: SEAMASTER Program water ballast and break bulk cargo summaries.
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TMC (Marine Consultants) Ltd. Stability & Global Strength
Telephone: +44 (0)20 7237 2617, email: [email protected]
www.tmcmarine.co.uk
SEAMASTER enables access of principal loading conditions, entry of deadweight items and
analysis of other intact/damage loading with vessel draught, trim, heel, stability and longitudinal
strength continuously updated and shown. The program provides detailed stability and strength
results giving a comparison between the calculated condition and the required or observed (draught
survey) condition.
Figure 3: SEAMASTER Program stowage plans.
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TMC (Marine Consultants) Ltd. Stability & Global Strength
Telephone: +44 (0)20 7237 2617, email: [email protected]
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Figure 4: SEAMASTER Program screen view showing stability and longitudinal strength results.
In summary, SEAMASTER has the following functionalities and calculates:
Draughts (at end perpendiculars, amidships, LCF, draught marks or at user defined locationson the hull sides/centreline);
Trim and list (dimension/angle); Displacements and hydrostatics, with sounding tables; Lightship weight breakdown; Deadweight items and groups breakdown; Intact/Damage compartments breakdown; Geometric loads (% compartment filling, or by weight); Non-geometric loads (varying length and specified centre of gravity); Free surface effects; Grain stability; Density variations; Suspended (crane) loads; Longitudinal strength (shear force, bending moment, torsion moment); Deflection amount (hog/sag).
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TMC (Marine Consultants) Ltd. Stability & Global Strength
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www.tmcmarine.co.uk
SEACOC (Cargo and Ballast Control)
Cargo operation control is a feature only available with the SEACOC module. This checks all the
intermediate stages of any complex loading/ballast operation. Entries for various compartments or
tanks are independent. To simulate loading (or discharge), start and finish times are required for
every hold. Ballasting and de-ballasting operations may be run simultaneously. Minimum steptimes are in 0.1hour intervals (6 minute intervals).
Other instances where SEACOC may also be used include transient voyage conditions, after
allowing for consumables, and also as part of a salvage tool in SEADAM after incorporating
aspects such as flooding rates and grounding.
Figure 5: SEACOC Module cargo operations control.
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TMC (Marine Consultants) Ltd. Stability & Global Strength
Telephone: +44 (0)20 7237 2617, email: [email protected]
www.tmcmarine.co.uk
SEAFLOOD (Flooding)
The flooding module in SEAMASTER allows for the ships waterline to move well above, or sink
well below, the assigned draught limit with excessive trim and list. Free-flooding of any space is
computed including the flooding of normally dry spaces such as the engine room, cargo spaces,
cofferdams and void spaces. A time simulation of the effect of water ingress can be chosen as analternative to the free-flooding option, which gives the state of the ship at any given time after the
size and position of the damage is input. Time-simulated flooding can be interrupted at any point in
time, which is useful for retrospective investigation, and can be combined with features such as air
pressurisation or applied pump rates for salvage.
Figure 6: SEAFLOOD Module damaged tanks and flooding.
In summary, the SEAFLOOD module has the following functionalities and calculates:
Flooding of compartments (partially filled, filled, stage flooding by step/time) andassociated draught, trim and list;
Observed draughts option; Damage hole size (within external or internal boundaries);
Flooding modes (down-flooding, up-flooding, cross-flooding; Hole size definition (exterior boundary / interior boundary); Floodwater ingress rate (time domain, cargo miscibility); Liquid cargo outflow rate; Permeability (volumetric); Pump rate option; Air pressurisation option; Geometric loads (% compartment filling); Non-geometric loads (unit/point loads); Grounding support type (single/two point, line); Tidal effects; Damage longitudinal strength (shear force, bending moment, torsion moment); Deflection amount (hog/sag).
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TMC (Marine Consultants) Ltd. Stability & Global Strength
Telephone: +44 (0)20 7237 2617, email: [email protected]
www.tmcmarine.co.uk
SEADAM (Wave Induced Loading)
Although the permissible hull bending moment and shear force for sea-going conditions take into
account the effect of waves, these values are assigned by Class in accordance with their rules (i.e.
maximum wave amidships). Wave loading for this purpose are arbitrarily determined for design
purposes. However, it is sometimes necessary to know what the actual loads are for a given waveheight, and heading. This may be particularly important following grounding, or if hull damage has
been sustained resulting in flooding resulting in reduced bending strength and stiffness (and/or
reduced shear and torsion strength).
Figure 7: SEADAM Module wave induced loading.
In order to determine wave-induced applied loading, SEADAM requires two of the main parameters
to be inputted: i.e. wave height, wave length and wave period. Accordingly, the wave shape
including slope is obtained. The crest location along the hull and incident angle may also be defined
and the influence on longitudinal vertical bending determined.
The ship is poised on a 2nd
order Stokes wave which is similar to a trochoidal wave. The wave
parameters can be altered as described above, and the related parameters are adjusted automatically.
Vessel draught and trim are automatically updated to obtain static equilibrium, and although this
ignores dynamic effects, any error involved is generally not considered large in the context of
uncertainties surrounding wave definition. Limitations of linear motion theory apply concerning
very high waves and the varying shape and size of hull.
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TMC (Marine Consultants) Ltd. Stability & Global Strength
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SEADAM (Grounding)
The seabed is defined either as Rock (i.e. force concentrated at the two specified points) or Sand
(force distributed over the whole length specified). If the water depths specified are less than
calculated free floating draughts, then the vessel is grounded.
All draught, stability and strength parameters are calculated based upon the location and value of
the ground reaction. If the water depths are less than the draught at one end or at a specific location
along the hull, then the vessel will trim (heel) about this location as a function of the longitudinal
(transverse) centres of buoyancy and ground reaction, calculated by the program using combined
moments of the displacement and the ground reaction.
If the water depths specified at the draught marks are all greaterthan the calculated free floating
draughts, then the vessel will automatically float free and the ground reaction is displayed as zero.
The calculated draughts in this case will simply be those obtained by hydrostatics in the normal
way. Tide may be incremented by gradual amounts (+/- 1 cm) and the stability and strength is
updated automatically.
Figure 8: SEADAM Module - screen view showing vessel during grounding analysis, with stability
and longitudinal strength results.
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TMC (Marine Consultants) Ltd. Stability & Global Strength
Telephone: +44 (0)20 7237 2617, email: [email protected]
www.tmcmarine.co.uk
SEADAM (Scantlings and Stresses)
SEADAM calculates the bending stress in still water or waves (any incident heading and wave).
Regarding structural response, stresses are calculated for each of the longitudinally continuous
structural members based on classic beam theory.
For an upright and intact hull, or in cases of symmetrical port/starboard damage and/or symmetrical
flooding, the resultant stresses calculated are about the horizontal axis with an accompanied vertical
shift of the neutral axis.
Damaged or wasted structure is represented in SEADAM by changing the efficiency (% loss) of
individual plates and stiffeners. For asymmetrical damage or flooding, the hull girder bending
characteristics change, with the neutral axis shifting vertically and to one side (i.e. vertically moved,
offset to the centreline and angled to the horizontal). In this case, the resultant stresses calculated
allow for combined bending about both the horizontal and vertical axes.
In summary, SEADAM calculates the residual strength capability of the vessel and this is used inthe context ofapplied loading by taking into account the loading condition and free surface effects,
and any flooding or grounding as determined in the SEAFLOOD module.
Figure 9: SEADAM Module intact/damage structure and calculated bending stress.
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TMC (Marine Consultants) Ltd. Stability & Global Strength
Telephone: +44 (0)20 7237 2617, email: [email protected]
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Figure 10: SEADAM Module damaged midship section and revised neutral axis.
In summary, the SEADAM module incorporates the following functionalities and calculates:
Geometrical definition of transverse section scantlings (continuous structural members); Reduction of scantlings due to wastage; Missing/deformed structure due to damage; Wave induced loading; Residual bending strength and stiffness calculated (i.e. applied stresses in the individual
structural members resulting from the longitudinal, vertical bending of the intact/damaged
hull girder);
Damage longitudinal strength (shear force, bending moment, torsion moment); Deflection amount (hog/sag).
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TMC (Marine Consultants) Ltd. Stability & Global Strength
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Figure 11: SEADAM Module damaged section and calculated residual strength.
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