Interesting debate ....
I think there is more than one type/ style/ design of helmet to suit the differing needs - ie an F1 helmet is a very serious bit of design / engineering to withstand the sort of forces it may encounter - its heavy - hence the introduction of the HANS system some years back to avoid the whiplash situation when the driver is very securley strapped to his machine.
Bikes/watersports, climbing etc all have differant 'needs' and potential loads - ie you can't strap a HANS device to anything on a bike , or in a boat etc - so the solution is much like Steves pic or a much lighter helmet to reduce the whiplash situation.
Its a trade off between added weight swinging about and spreading the force of an impact, to giving the 'head' greater time to decelerate etc.
As for them on boats ? Racing yes by all means - Zapcats - yes why not ( I think there may be more whiplash type problems as a result ? )
Normal ' stuff' on a RIB - personal choice seems to work .