Originally Posted by robineff
I have never been sure if these limits are 'through the water' or 'over the ground'. I would welcome some guidance.
I'm pretty sure they will be 'through the water' limits. Although I wonder how lenient a harbour master would be, if say you were doing the speed limit (didn't have a gps, so couldn't tell what over the ground you were doing) but with 3 knots of tide were in effect breaking it. I guess they'd certainly not bother with you, unless you were umoungst a school of kids in sailing dinghies in a harbour like christchurch.
I think this entire subject comes down to the situation when you get caught. As above, if you are exeeding a limit in a dangerous situation, or when you could endanger someone else on the water, then you do deserve to get booked - on the other hand I have heard that speeding fines being handed out in chichester harbour, for example, are avoided by the harbour master and generally they prefer to give you a good 'b*llocking' before letting you go. (this generally has a better effect on everyone anyway) - It also costs the harbour authority a fortune apparently everytime they have to take someone to court.
Most of the speed limits are set in these harbours to stop shore line erosion - which seems a bit mad, when I consider my RIB kicks out a ten times bigger wake when the whole hull is dragging through the water at 8 knots than it does at 15 or 20! But there we go!