Note that in the Data window, there are three main columns. The first column contains explanations of the data in a particular row, the second column contains the data itself, while the third column contains the units for the data in that row. An extra column is added for each of the analysis methods used; data required for that method are copied into the new column.

Data may be typed into any column apart from the first and third columns. Changing any part of the data for a method will change that same piece of data for all methods, i.e. changing the length in any column will change the length in every column.

Note:

Input parameters: length; volume; prismatic coefficient and max sectional area are related by the formula below.
 
If data is measured from a design then this data will be consistent. However if the data are entered manually, Hullspeed will recalculate these values to maintain consistency. If either length (L), volume (Ñ) or Prismatic Coefficient (C_P) are entered, then Max Sectional area (A_X) will be recalculated. If A_m is entered then C_P will be recalculated.

The required data are as follows:

The length of the hull, measured on the waterline.

The maximum submerged width of the hull.

The maximum submerged depth of the hull.

The volume of seawater displaced by the hull.

The submerged surface area of the hull.

For the slender body method, the wetted area is used to calculate the Friction and Viscous resistance coefficients only (the wave resistance is calculated directly from the surface model).

The wetted area is also used to calculate the resistance coefficients displayed in the Graph window.

A measure of the extent to which the submerged volume of a hull fills a prism defined by the submerged length, multiplied by the area of the largest transverse section; i.e.

A measure of the extent to which the area of the water plane fills the rectangle defined by the length * beam; i.e.

The angle measured in the plane of the water plane, between the hull and the centreline.

The distance to the longitudinal centre of gravity, measured from amidships. Note that this distance is positive forward. I.e., an LCG 1.5m aft of midships will be entered as -1.5 .

Note that when Hullspeed measures a hull, it assumes that the vessel is in hydrostatic equilibrium at the DWL and the LCG is assumed to be at the LCB (longitudinal centre of buoyancy.

The submerged sectional area of the transom, measured when the vessel is at rest.

The largest submerged sectional area of the hull, measured when the vessel is at rest.

The transverse sectional area of the bulb (if any) measured on the waterline at the stem.

The distance from the keel line, to the transverse centre of area of the bulb section on the waterline at the stem.

The submerged surface area of the hull.

The draft at the fore perpendicular. This value can be left at zero, whereupon Hullspeed will assume it is the same as the value for the ‘draft’ item.

The deadrise, as measured at midships.

The area of the vessel above the waterline, when viewed from the front. Set to zero to ignore wind resistance.

The coefficient of drag for calculation of wind resistance. Expected values would be in the range of 0.8 - 1.2.

The air density, at the appropriate ambient temperature. 1.293 kg/m^3 at 15 deg. C.

The wetted area of appendages, used to calculate appendage drag. Set this to zero to ignore appendage resistance.

This is a nominal length for the appendages which is used to calculate the Reynolds Number at which the appendages are operating. This Reynolds Number is used to calculate the skin friction drag of the appendages using the ITTC’57 formulation. Typically this length would be representative of the rudder (and keel, if applicable) chord.

A factor for estimating the resistance due to the drag on appendages. Expected values range from 1.0 to 3.0.

A factor for accounting for variations between model tests and full-scale trials. This factor is included only for the analysis methods which used a correlation allowance in their original formulation: Savitsky pre-planing; Lahtiharju; Van Oortmerssen and Series 60. The Holtrop method includes an implicit correlation allowance which is included at all times. The correlation allowance, or DC_F, may be estimated from the ITTC recommended formula:

Where k_S is the hull roughness; typically 150x10^-6m and L is the waterline length of the hull in the same units.

The values for the density and kinematic viscosity of the water may be edited by the user. The ITTC’57 values for salt water (3.5% salinity) at 15°C., for density and kinematic viscosity are as follows: density 1025.9 kg/m^3 and kinematic viscosity 1.18831x10^-6 m^2/s.