sailquik said..
Yes. Who did that and where are the findings?
Oh hang on. This is not the British surfboard study is it?

Delft towing tank, 1983. Not done by me, but I was present as observer/assistant. 1/2 scale boards and fins due to size/speed limitations of the towing tank.

One interesting result was showing ventilation (or possibly cavitation) of the tip vortex, visible in the photo on the nearest fin in the photo I posted. Tip vortex cavitation can occur at high speeds, but you would need to use a cavitation tunnel to determine which it was.

There were a couple of other interesting results, but I'll try to contact the researcher and see if i can get a copy of the original report to back up my recollections.

32.5 lbs is the answer for drag.....according to Jim Drake and not the Hitchiker's Guide!

Drag is relative to speed and AoA... so any single number is completely meaningless. I think 42 is a better number.

That's it Ian, you found it. Jim's analysis of windsurfing, best one I've found to date. Sadly he never broke down the drag figures into individual components before he passed away. It's a good reference to establish a base point for calculations and testing. Have built the AFTTR to withstand 200 pounds of force when testing flex/twist of fins and foils.

Almost finished 3d printing the test components for the lift/drag experiments, just waiting for a weather window to start testing, still a bit chilly here!

Here's the little buggers, the first batch of 3D Roodents for testing. Had to develop a complex algorithm to shape and scale them for differing chord-lengths. Modeled in Solidworks before printing on a Prusa. If testing is encouraging will build some molds to make them from more flexible materials.

Pacey said..

sailquik said..
Yes. Who did that and where are the findings?
Oh hang on. This is not the British surfboard study is it?

Delft towing tank, 1983. Not done by me, but I was present as observer/assistant. 1/2 scale boards and fins due to size/speed limitations of the towing tank.

One interesting result was showing ventilation (or possibly cavitation) of the tip vortex, visible in the photo on the nearest fin in the photo I posted. Tip vortex cavitation can occur at high speeds, but you would need to use a cavitation tunnel to determine which it was.

There were a couple of other interesting results, but I'll try to contact the researcher and see if i can get a copy of the original report to back up my recollections.

I've got a copy of the original report now, but I see I can't post PDFs to this forum. Anyone who wants a copy, email me at optimar at me dot com and I'll send you the PDF files.

A bit of background, this research was done by Pjotr van Schothurst, a student at Delft University in Holland in 1983, I assume as his final year project for his Naval Architecture degree. So the good news is that the report is quite comprehensive, covering three different board designs and 4 different fin configurations, bad news is that it is in Dutch.

It was done in the Delft towing tank, and more than 200 runs were performed, so a lot of good data.


I was responsible for delivering the 3 test boards, 1/2 scale models shaped by Tris Cokes of Limited Edition in Cornwall, to Pjotr in Holland, as I was doing some speed sailing contests in the area at the time. I got to help out for a couple of days and observe all the testing so I know it was good quality work.