Great find Choco!

Interesting read for sure.
My biggest observation about this is that almost all of my big crashes in speed windsurfing have been at speeds around 20-24 m/s,
(38-44 Knots). In every case I can remember, (yes, "remember" that is a big qualification!

) I landed more or less on my back and BOUNCED and skimmed/rolled over the water for a while. A cant say I have ever had a fall where my head pierced the surface, at least until I had slowed considerably. (I have worn a Helmet, either a canoeing or a Ski/Skate helmet for almost all my windsurfing 40+ years).
And yes, I can say after a few of those crashes I woke up the next morning with quite sore, front of neck muscles from the muscles resistance to my head being thrown back as I hit the water on my back, or possibly because my body was jerked by my attachment to the harness and boom as they inevitably broke!!.

But I would be very surprised of the helmet made any significant difference to that.
On the other hand, I have experienced quite a lot of times where my head has slammed hard into the mast or sail. I was very glad to have the impact protection in those cases.

Bounce/skim example where Mat crashed at 41 Knots! loving the excuse to share this again!