NavCad is the industry-standard software for boat and ship speed-and-power analysis. This tutorial provides a structured, step-by-step workflow to predict hull resistance and analyze propulsion performance. Introduction to NavCad Workflow
NavCad operates on a sequential data model. Accurate analysis requires completing four distinct stages in order: Vessel Definition: Entering hull dimensions and parameters.
Resistance Analysis: Selecting and running empirical prediction methods.
Propulsion Analysis: Defining the propeller geometry and mechanics.
System Matching: Aligning the engine, gear, and propeller operating curves. Step 1: Set Up the Project and Units
Before entering data, define your environment and alignment parameters. Open NavCad: Start a new project file (.ncd).
Configure Units: Navigate to Options > Units. Select your preferred system (typically Metric/SI for commercial ships or English/Imperial for US recreational vessels).
Define Fluid Properties: Enter the water temperature and salinity. NavCad automatically calculates density and kinematic viscosity, which directly impact frictional resistance calculations. Step 2: Input Vessel Dimensions (Hull Data)
The accuracy of your resistance prediction depends entirely on the geometric coefficients entered in the Hull tab. Primary Dimensions: Input Length on Waterline ( LWLcap L sub cap W cap L end-sub ), Beam on Waterline ( BWLcap B sub cap W cap L end-sub ), and Draft (
Displacement Parameters: Enter the total displacement mass or volume. Form Coefficients: Input the Block Coefficient ( CBcap C sub cap B ), Prismatic Coefficient ( CPcap C sub cap P ), and Midship Section Coefficient ( CMcap C sub cap M
). NavCad will cross-check these values for mathematical consistency. Wetted Surface Area ( WSAcap W cap S cap A ): Input the exact WSAcap W cap S cap A
from your 3D CAD/Hydrostatics software. If unavailable, use NavCad’s built-in regression formulas to estimate it. Step 3: Define Operating Modes and Speeds
Establish the parameters for how the vessel moves through the water.
Configuration: Select the hull type (e.g., Monohull, Catamaran) and mode (Displacement, Semi-Displacement, or Planing).
Speed Range: Define your speed array in the Operating Profile. Enter the minimum, maximum, and cruise speeds (typically in knots) using a consistent increment (e.g., 2-knot intervals) to generate a smooth curve. Step 4: Run the Resistance Prediction
NavCad utilizes standard empirical methods (such as Holtrop & Mennen, Oortmerssen, or Savitsky) to calculate total resistance ( RTcap R sub cap T
Select the Method: Go to the Resistance tab and open the method selection assistant. NavCad evaluates your hull coefficients against the validity ranges of its internal database. Choose the method with the highest compatibility score. Account for Margin Factors: Add a Correlation Allowance ( CAcap C sub cap A ) to account for real-world hull roughness.
Input Appendage Drag: Specify the surface area and drag coefficients for rudders, shafts, struts, or thruster tunnels.
Input Wind Drag: Enter the vessel’s frontal area and wind aerodynamic coefficient. Calculate: Click Compute. Review the Total Resistance ( RTcap R sub cap T
) versus Speed graph to ensure there are no abrupt numerical spikes. Step 5: Define the Propulsion System
Once you know how much force is required to push the ship, you must configure the system that generates that force.
Select Propeller Type: Choose your propulsors (e.g., Open Propeller, Ducted Propeller, Waterjet) and enter the number of shafts.
Input Propeller Geometry: Define the blade count, expanded area ratio ( EARcap E cap A cap R ), and initial Pitch-to-Diameter (
Determine Hull-Propeller Interaction: Input the Wake Fraction ( ), Thrust Deduction ( ), and Relative Rotative Efficiency ( ηReta sub cap R
). You can input these from Model Test/CFD data or use NavCad’s empirical estimation routines. Step 6: Perform System Matching and Engine Selection
The final stage matches the propeller’s power demand with an engine’s available power output.
Input Engine Data: Enter the Rated Power, Rated RPM, and the engine’s torque curve limits.
Input Gearbox Efficiency: Define the mechanical transmission efficiency loss (typically 2% to 5% for direct shafts). Run System Analysis: Execute the Propulsion calculation.
Evaluate Results: Check the Operating Equilibrium point. Ensure that the propeller absorbs the engine’s power without exceeding the engine’s maximum torque limit or causing critical propeller cavitation. Step 7: Export Reports and Graphs
NavCad generates comprehensive documentation for design verification or client review. Graphs: Plot Shaft Power ( PScap P sub cap S
) vs. Speed, Fuel Consumption vs. Speed, and Cavitation Inception limits.
Export: Save the data sheets as a PDF report, or export the raw curves to a spreadsheet (.csv) for further design optimization in external CAD environments.
To help tailor this workflow, could you share a bit more about the vessel type you are analyzing (e.g., commercial displacement ship, planing boat, catamaran)? If you have a specific empirical method in mind or want to focus on a particular propulsion setup, let me know so I can expand on those details.
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