This is the rule.
For every record attempt on a WSSRC approved course, there must be a minimum depth of water, which is defined as follows.
At the time of the run in question, the shallowest part of the course must be covered by water with a depth of at least half the static immersed beam of the craft involved, or 10cm, whichever is the greater. (Guidance note To define the depth requirement, the craft or board involved should be afloat and the widest part of the hull or hulls touching the water should be measured. In the case of a multihull, the widest hull is measured or hydrofoil if fitted). In the case of an event involving a number of competing craft, the WSSRC Commissioner can announce at the commencement of the event what the minimum depth requirement will be.
I think these runs didn't count because they were outside the days listed for attendance by the officials who time the records. The yachts have an advantage with their onboard data being accepted.
http://www.sailspeedrecords.com/the-cou ... 500-m.html
Interesting in the video, that although the course has very tiny wavelets, they show up clearly in the wake.