Delft VPP

Hey you incredibly knowlegeable people. Help.

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?

Thanks in advance.



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.

How well the Delft drag prediction will work for you, depends on a few things.
[li]What version of delft Prolines is using, delft has 3 versions. The last one was published in 96.[/li][li]If your design is right in the middle of the delft parameter space, it will most likely give you decent drag estimations. If one of your hulls parameters is outside of the range, the drag estimation will most likely be off.[/ul]This paper talks about all 3 versions of delft, and gives you the coefficients used in series 3.[/li]

this is the type of design discussion i can really sink my teeth into.

That is exremely helpful. Thank you


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).