Ship ResistanceSavitsky

Ship ResistanceSavitsky
Menu location
Resistance → Resistance Savitsky prediction
Workbenches
Ship
Default shortcut
None
Introduced in version
-
See also
None

Description

Calculates ship resistance by the Savitsky method. This method was formulated by Daniel Savitsky in 1964 [1], with application to fast vessels in a planing regime.

Plots the resistance curve, the equilibrium trim, the power prediction and the resistance coefficients. It also exports the results to a spreadsheet.

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  Resistance graph obtained by Savitsky method.

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  Equilibrium trim graph obtained by Savitsky method.

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  Power graph obtained by Savitsky method.

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  Resistance coefficients graph obtained by Savitsky method.

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  Spreadsheet generated by Savitsky method.

Resistance graph

The resistance is represented in kN, as a function of speed in knots. It includes the total resistance, the total resistance and the pressure resistance.

Trim graph

The equilibrium trim is represented in degrees, as a function of speed in knots.

Power graph

The power is represented in kW, as a function of speed in knots. It includes the effective power and the break power.

Coefficients graph

The resistance coefficients are adimensional, they are represented as a function of speed in knots. It includes the effective power and the break power.

Exported Spreadsheet Data

The spreadsheet contains the values of different variables for each evaluated speed, separated by columns.

Variable	Unit
Speed	kn
Trim	°
Total resistance	kN
Friction resistance	kN
Pressure resistance	kN
CF ×10³	-
CP ×10³	-
CT ×10³	-
EKW (Effective Power)	kW
BKW (Brake Power)	kW

Application limits

It must be taken into account that the obtained results represented in the graphs must be inside the application limits of the method.

The application limits of the Savitsky method are:

${\displaystyle 1.0\leq C_{V}\leq 13.0}$

${\displaystyle 2.0^{\circ }\leq \tau \leq 15.0^{\circ }}$

${\displaystyle \lambda \leq 4.0}$

Where:

• ${\displaystyle C_{V}}$ is the velocity coefficient, defined by the following expression:
  ${\displaystyle C_{V}={\frac {V}{\sqrt {gB}}}}$
• ${\displaystyle \tau }$ is the trim angle of the vessel.
• ${\displaystyle \lambda }$ is the dynamic length-to-beam ratio, defined by the following expression:
  ${\displaystyle \displaystyle \lambda ={\frac {L_{K}+L_{C}}{2B}}}$

Usage

This tool does not have a strict dependency on a Ship instance(see Ship CreateShip), which means that it is possible to use it introducing the necessary ship data values in the dialogue.

Using ship geometry

In order to execute the method, select a Ship instance and invoke Resistance → Resistance Savitsky prediction.

The ship data will be obtain from the ship and the user only needs to enter the boundary conditions. Data obtained from the vessel can be edited.

Using ship data

In order to introduced the ship data manually, invoke Resistance → Resistance Savitsky prediction and fill the dialogue fields.

Tutorials

• FreeCAD-Ship s60 tutorial
• FreeCAD-Ship s60 tutorial (II)

References

[1] D. Savitsky, “Hydrodynamic design of planing hulls,” Marine Technology, Octubre 1964.