• What is NavCad?
• What is the "minimum hull drag" analysis?
• What is the Method Expert?
• What propulsor types are supported by NavCad?
• Can NavCad evaluate cupped propellers?
• How do I use my Kt/Kq model test data?
• Tell me about waterjets in NavCad.
• Can I create my own programs with the NavCad Personal Developer Library?

NavCad™ is a software tool for the prediction and analysis of vessel speed and power performance. It also provides for the selection of suitable propulsion system components - engines, gears and propellers.

NavCad is based on a "document-centered" architecture, correctly known as a Multiple Document Interface. In other words, the main NavCad window contains and processes graphs, as well as controls the operation of the data entry and calculations. Most Windows business applications (e.g., word-processors, spreadsheets) are arranged in much the same way.

At the top of the window is the Main Menu (File, Edit, etc.) containing the many menu commands which bring up data entry forms and launch calculations. Immediately underneath is the Toolbar with buttons for frequently-used commands. To the left of the screen are the Resistance Build View and Propulsion Build View. To the center/right is the Graph Window. On top of the graph is the Performance Summary spreadsheet.

 
Once hull data has been entered and a resistance prediction built, you can analyze and optimize your hull with the Minimum hull drag analysis. You define search ranges and intervals for significant data items (e.g., length, beam, LCB), and NavCad predicts the drag for the configurations and then ranks it. The configuration with the minimum drag is displayed at the top of the list, with the difference from minimum displayed in percent of drag. The calculation also has the ability to review a compromise analysis, using a weighted average of two speeds.

 
NavCad contains HydroComp's Method Expert prediction method ranking system. This feature takes your vessel data and ranks all monohull prediction methods based on speed regime, ranges of hull parameters and the availability of hull details (e.g., if waterplane coefficient or trim, for example, has been entered and is used in the method). It also takes into account HydroComp's extensive knowledge about prediction method behavior and reliability. Warnings are raised if a method has shown poor results for the given vessel information.

 
NavCad greatly extends your propulsor options. In addition to the popular B-series, Gawn and Kaplan propellers, NavCad includes surface-piercing and cycloidal propellers, cupped propeller prediction, use of custom Kt/Kq data and waterjets.

 
NavCad's prediction of cupped propeller performance is based on novel developments from HydroComp's technical staff. The results of this study were presented at SNAME Propellers '97 [MacPherson, D.M., Small Propeller Cup: A Proposed Geometry Standard and a New Performance Model]. A version of this prediction technique has been used in HydroComp PropExpert™ since 1997 with great success.

 
You can enter and save Kt and Kq versus J data from your propeller model tests or wake-adapted calculations. These simple ASCII files are then used as the source of propeller performance for Propulsion calculations. NavCad even properly applies scale correction during the calculations.

New to NavCad in 2005 is the propeller Aligned series prediction, which correlates a series prediction to a user-defined Kt/Kq file. This allows the user to alter the series' prediction based on the performance of the model. The resulting Kt/Kq figures reflect the qualitative "shape" of the underlying series, with a quantitative correction derived from the propeller model.

 
After a number of years of looking at the problem of waterjets, we concluded that a suitable first-principals solution was not possible. Part of our review included the development of two new coefficients - coefficients which would allow waterjet performance to be defined in a manner suitable for NavCad's ASCII file formats. Through the use of these new coefficients, the waterjet calculation algorithm determines the proper thrust and power for a given speed and equilibrium RPM.

 
Included with NavCad is the NavCad Personal Developer Library (PDL). The NavCad PDL is a DLL "wrapper" around NavCad to provide external access to NavCad's internal data items and functions. As an ActiveX DLL, it can be attached to almost any programming environment that supports these components. Visual Basic, however, is the most popular platform for programming the NavCad PDL, especially from within Microsoft Excel.

Please contact HydroComp for more information about the Personal Developer Library.