Laser (ILCA) S-turn technique when sailing downwind

This simulation was inspired by Riley Schutt's doctoral dissertation "UNSTEADY AERODYNAMICS OF SAILING MANEUVERS AND KINETIC TECHNIQUES" at Cornell University. Shutt and his team equipped a Laser with an array of camera's & sensors to record all the motions and sail shape changes of the boat while sailing. In addition to the S-turn downwind sailing technique, he looked at leech flicking upwind and roll tacking.

In our first simulation, we look at the S-turns. Quite complex, with simultaneous heading changes (S-turns), rolling of the boat (heel), sheeting & twisting of the sail and the sailor's motions. We also added a Windex to the mast top to record the apparent wind changes (inset). The variation of the apparent wind angle during one S-turn cycle is up to 90 degrees.

The rock&roll increases the driving force of the sail quite dramatically, up to 75%. The increase appears to be sensitive to the timing of the mainsheet adjustments, and of course, the amount of roll.

(c) WB-Sails 2022

[ajohncant]

Awesome simulation and really interesting results!

Really interesting to know that you can get so much extra power out of these S-turns. They definitely gain you a few places near the back of the UK ILCA nationals.

Got to add this dissertation to the reading list. My understanding was that these turns helped you surf the waves, and keep your speed up, while not ploughing forward into the next wave until you see a gap. However, it never made sense why it was faster than surfing diagonally down the waves for several boat lengths in alternate directions (which wasn't faster than someone sailing in a straight line when I tried it)

[PeterLaFontaine-hb]

These are awesome, cam you do more simply fascinating

[timstorey]

It would be interesting to see the results of this study at different wind speeds. I imagine that the differences in downwind angles to sail an asymmetric spinnaker boat downwind in light vs heavy wind would be relevant to how to sail a laser downwind in various wind speeds also.

[casatv]

Awesome! You should make one on snipes sailing downwind, with the pole and the flying jib and no spinnaker...

[mjuliofranco]

Awesome!! Brilliant model! Thanks for sharing,

[d_sparrow]

This is amazing! Thanks a lot for sharing!!

[ross.venner]

Interesting, I shall attempt to apply this in my lowrider Hawkmoth. The scows have us beat in the lightest of light airs because they can reduce their wetted surface so dramatically by healing.

[sankdom]

Should I pull up my center board for the s turn? I'd assume so right but wouldn't that make it a little harder to turn accurately

[Alexandra-qwhp]

Super interesting. What do you think is the impact of the frequency? Does it also help to do the S turn, trimming and rolling more slowly? (That way you don't risk to get a penalty.)

[大阪北港ディンギークラブ-lk]

Awesome!
Thank you a lot, we learned a lot from it!

[JamesFosterSailing]

What is the equivalent underwater part of the problem; the increase in driving force isn't the full story as you are generating more drag from turning, but there are also rolling benefits to the underwater side too.

[vincenthontarrede]

Do you have implemented transition models for the intralaminar characteristics of the viscous sublayer? And what is your Reynolds Number please ? Y+ value would also be intersting to know

[mikemalloy]

how does that square with Rule 42, for ILCA Lasers?

[captainsirjackchucklebutty]

Ask Sir Ben ! He would never tell you all this. Top secret !

[isaacislaughter]

International laser class association, " formerly known as laser" ?🤨
Super interesting at any rate..cheers

[trackie]

Great information, though I would have preferred actual human voices narrating. I muted and used captions instead.

[viesturssimsons]

You will probably get a penalty for this, at least with bad judges definitely

[ILCALaserSailor]

This is great thank you for sharing! #ilcalasersailor @ilcalasersailor