There's a helpful article in the Telegraph which describes its contents as a red inflatible (liferaft) and wooden boards (saloon sole).Yacht was at anchor yesterday in the bay today ashore at the east end of the bay (splash point) with two people rescued.
Got to disagree with your weather assessment. Wind picked up significantly late afternoon to 20 knots plus SW in Hove, I'm sure that stretch would have been a bad place to anchor at least early evening.That looks like a shockingly unforgiving place to have trouble.
Thursday was a pleasant sunny day with light breeze, maybe a delivery trip with the new owner gone wrong as the weather turned overnight.
There's a long list of sold boats that have left MYC and not made it past the Forts a couple of miles away, the most recent last Saturday. You don't hear about these as they only hit the mud and get off unscathed when the tide returns.