Ahh, Thank you Duncan,
At least I wasn't just imagining it!
I would guess that if carefully sited, the risk of impact could be minimised. On one of our old RIBs the filters were tucked in-between the sloping, reinforcing stringers (not sure if that is the correct term?) that braced the transom. This meant that they were relatively protected.
Pete and Jono are obviously better at keeping random cr~p off of their boat and that is to be applauded. Sometime ago, before I knew any better, I'd come off of waves and whilst the boat had landed, half the gear was still on its way down
The MCA Guidance note is quite a good reference source though, and would apply if you wanted to use the RIB for commercial operations.