NavCad FAQ

• 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 to use with NavCad?

What is NavCad ?

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 built around a multiple document interface for reports and graphs. This interface also holds a Project View and a Performance Summary.

The Project View contains a tree (much like Windows Explorer) that you can use to quickly open data entry forms and run calculations. It also contains a "snapshot" of the project's principal parameters - such as Displacement, L/B or engine power.

The Performance Summary is a spreadsheet of the current system performance. It is a complete look at the results of your project calculations, from resistance all the way through engine power, fuel rate and cavitation. The Performance Summary also underscores the fundamental nature of NavCad - where all performance items are related through a Hull-Propulsor-Engine equilibrium.

Sample NavCad main screen

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 time-weighted average of two speeds.

Sample NavCad minimum hull drag screen

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.

Sample NavCad Method Expert screen

NavCad greatly extends your propulsor options. In addition to the popular B-series, Gawn and Kaplan propellers, NavCad 3.6 includes surface-piercing and cycloidal propellers, cupped propeller prediction, use of custom Kt/Kq data and the much anticipated waterjets.

Propulsor screen

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.

New file types have been added to allow you to enter 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 Shaft Power and System Analysis calculations. NavCad even properly applies scale correction during the calculations. At the current time, these files cannot be used for Optimum Propeller calculations (since the propeller P/D ratio, number of blades and blade area ratio are already defined).

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.

Like all NavCad files, the format for the waterjet files is available from HydroComp. We also provide a Microsoft Excel template to help create waterjet files. Many files are already being made available to NavCad users who are up-to-date on their support and update subscription.

In much the same way as NavCad can be run from other programs, you can launch other programs from within NavCad. Standard ASCII-based NavCad job files are used as the data exchange format.

Sample NavCad user application screen