Hydrostatics#

TankOptions#

class TankOptions(include_mass=False, include_fsm=True)#

Options for tank handling in hydrostatic calculations.

Parameters:

  • include_mass – Include tank fluid mass in displacement (default: False)

  • include_fsm – Apply Free Surface Moment correction to GM (default: True)

static none()#

Create options with no tank effects (mass=False, fsm=False).

static all()#

Create options with all tank effects (mass=True, fsm=True).

static mass_only()#

Create options with only mass included (mass=True, fsm=False).

static fsm_only()#

Create options with only FSM correction (mass=False, fsm=True).

include_mass: bool#

Whether tank mass is included.

include_fsm: bool#

Whether FSM correction is applied.

HydrostaticsCalculator#

class HydrostaticsCalculator(vessel, water_density=1025.0)#

Calculator for hydrostatic properties.

Parameters:

  • vessel – The vessel to calculate hydrostatics for

  • water_density – Water density in kg/m³ (default: 1025.0 for seawater)

from_draft(draft, trim=0.0, heel=0.0, vcg=None, num_stations=None, tank_options=None)#

Calculates hydrostatics at a given draft, trim, and heel.

Parameters:

  • draft – Draft at reference point (m)

  • trim – Trim angle (degrees)

  • heel – Heel angle (degrees)

  • vcg (float or None) – Vertical center of gravity for GM calculation (optional)

  • num_stations – Number of stations (optional)

  • tank_options – TankOptions object (optional)

Returns:

HydrostaticState with all properties

from_drafts(draft_ap, draft_fp, heel=0.0, vcg=None, tank_options=None)#

Calculates hydrostatics from drafts at Aft and Forward Perpendiculars.

Parameters:

  • draft_ap – Draft at Aft Perpendicular (m)

  • draft_fp – Draft at Forward Perpendicular (m)

  • heel – Heel angle (degrees)

  • vcg (float or None) – Vertical center of gravity for GM calculation (optional)

  • tank_options – TankOptions object (optional)

Returns:

HydrostaticState with all properties

from_displacement(displacement_mass, vcg=None, cog=None, trim=None, heel=None, tank_options=None)#

Calculates hydrostatics for a given displacement, finding the required draft.

Parameters:

  • displacement_mass – Target displacement in kg

  • vcg – Vertical center of gravity (m) for GM calculation (optional)

  • cog – Full center of gravity (LCG, TCG, VCG) tuple (optional, overrides vcg)

  • trim – Fixed trim angle in degrees (optional, default 0.0)

  • heel – Fixed heel angle in degrees (optional, default 0.0)

  • tank_options – TankOptions object (optional)

Returns:

HydrostaticState with all properties

Note

When tank_options is provided with include_mass=True, displacement_mass is interpreted as the mass of the vessel excluding the fluid in the tanks. The total displacement used for calculation will be displacement_mass + tank_fluid_mass.

HydrostaticState#

class HydrostaticState#

Result of hydrostatic calculations.

Basic Properties

draft: float#

Draft at Midship Section (MP) in meters.

draft_ap: float#

Draft at Aft Perpendicular (AP) in meters.

draft_fp: float#

Draft at Forward Perpendicular (FP) in meters.

draft_mp: float#

Draft at Midship Perpendicular (MP) in meters (alias for draft).

volume: float#

Submerged volume (m³).

displacement: float#

Total displacement mass in kg (Volume * Water Density). Represents the total weight of the floating system (Vessel + Tanks).

vessel_displacement: float#

Vessel displacement mass in kg (Total - Tank Mass). Represents the input displacement (Lightship + Deadweight excluding tanks).

tank_displacement: float#

Tank fluid mass in kg (sum of all tank fluid masses). 0.0 if include_mass is False.

Centers

cob: tuple[float, float, float]#

Center of Buoyancy (LCB, TCB, VCB) vector.

cog: tuple[float, float, float] or None#

Center of Gravity (LCG, TCG, VCG) vector, if provided. Matches displacement.

vessel_cog: tuple[float, float, float] or None#

Vessel Center of Gravity (LCG, TCG, VCG) vector (Ship-only). Matches vessel_displacement.

Waterplane Properties

waterplane_area: float#

Waterplane area (m²).

lcf: float#

Longitudinal Center of Flotation (m).

Metacentric Radii

bmt: float#

Transverse metacentric radius (m).

bml: float#

Longitudinal metacentric radius (m).

Metacentric Heights (Corrected for Free Surface)

gmt: float or None#

Transverse metacentric height (Wet/Corrected) (m).

gml: float or None#

Longitudinal metacentric height (Wet/Corrected) (m).

Metacentric Heights (Uncorrected)

gmt_dry: float or None#

Transverse metacentric height (Dry/Uncorrected) (m).

gml_dry: float or None#

Longitudinal metacentric height (Dry/Uncorrected) (m).

Dimensions

lwl: float#

Length at Waterline (m).

bwl: float#

Beam at Waterline (m).

los: float#

Length Overall Submerged (m).

wetted_surface_area: float#

Wetted Surface Area (m²).

thickness_volume: float#

Volume added by the hull plate thickness (m³).

contact_surface_area: float#

Shared area between hulls excluded from wetted surface (m²).

midship_area: float#

Midship Section Area (m²).

Form Coefficients

cb: float#

Block Coefficient.

\[C_b = \frac{\nabla}{L_{wl} \cdot B_{wl} \cdot T}\]
cm: float#

Midship Section Coefficient.

\[C_m = \frac{A_m}{B_{wl} \cdot T}\]
cp: float#

Prismatic Coefficient.

\[C_p = \frac{\nabla}{A_m \cdot L_{wl}}\]

Free Surface Corrections

free_surface_correction_t: float#

Transverse Free Surface Correction (m).

free_surface_correction_l: float#

Longitudinal Free Surface Correction (m).

Stiffness Matrix

stiffness_matrix: list[float]#

6x6 Hydrostatic Stiffness Matrix (flattened row-major).

Advanced Properties

sectional_areas: list[tuple[float, float]]#

Sectional Area Curve as list of (x, area) pairs.

freeboard: float or None#

Minimum freeboard in meters, or None if no deck edges defined.