Flying Fifteen Sailboat CFD

At the recent RYA Dinghy Show I was reminded that last year I had discussed trying out Simerics’ new Marine-CFD template on a Flying Fifteen hull.  The idea of this was more to see whether it could illustrate the importance of keeping the boat flat, etc. rather than to try improve the design within the limits of strict one design rules.

At the show Keith Jamieson found some old measurement diagrams on his laptop which he e-mailed on to me.  I have tried to make these into a 3D geometry, but currently this probably doesn’t pass the “batten test”.  Anyway I tried running a free surface CFD simulation on this last night and here are some initial results.  These are equivalent to a tow tank test on flat water with a speed of 10 knots.

ff15_10knt_upper2

ff15_10knts_side

This second image is probably indicating that the model is currently sailing in a very bow down attitude.  This is because I set the Centre of Gravity as being 3.75 m in front of the transom which in hindsight is probably far too far forward.  Has anyone ever calculated where it would be in a Flying Fifteen with two people on board?

ff15_10knts_underside

This image shows the poor quality of my geometry and how it is  inducing additional drag.  Back to the drawing board!

So the next steps are to tidy up this hull geometry and then find some decent drawings of the keel and rudder so I can add those to the model.  Of course, this shape is based on the 1993 measurement diagrams so they will not illustrate any differences between the Mark 9 and 10 designs.  To do this I would need to obtain some scanned geometry from somewhere.

By the way, if anyone ever wondered what it would be like being towed in a Flying Fifteen at 15 m/sec (30 knots) I did run the simulation at that speed by mistake …

ff15_15ms

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