I have just forked out on a Vacanti Yacht Design Prolines hull design program.
It comes with a version of the Delft VPP.
I know that the Delft system is validated for full sizes yachts of moderate beam/length and displacement/length ratios.Howevr, its results are said by Vacanti) to be indicative of trends way outside these limits at dipacement speeds.
Does anyone have any data (anecdotal or otherwise) on what this means? Any practical experience of the VPP in long, thin, light models?
The delft series is used to calculate hull drag for a given fn number. Most VPP use delft to predict hull drag, but hull drag is only part of a VPP. If a salesman told you delft is VPP you need to have a conversation with his manager.
I think Dan is on the money here. Some years ago I took the “latest” Delft coefficients and used them in a spreadsheet to create a start on a rough IOM VPP. I abandoned the task very quickly because it gave nonsense when I fed it IOM dimensions and displacements, while reproducing perfectly plausible results for 30 foot keel boats… I have some connection with the Wolfson Unit at Southampton who provide a commercial VPP (used by the IOM rating office, I believe, and by Team NZL, amongst others), and they supply a “special” version to anyone who wants to use it on model yachts. They refuse to say what is “special” about their special version, but it gives different predictions from its “full size” equivalent when given data about boats 2 ft long (smile).