It all depends on so many variables. Are you on a wide open lake or on a river, cut-up by islands that restrict your sighting distance ? Compare boating during a full moon on a flat surface with little background lights to no moon, lots of lights and lots of traffic, perhaps some of it commercial boats, and toss in some unlit buoys and lobster pots. A speed limit that's set for the latter will be too slow for the former, and consequently ignored just like the SLs on our highways. Certainly you can go too fast for even the best conditions but "minimum planing speed" is too slow (at least where I boat). Just like we supposedly do on our roadways, you set a SL for the optimal conditions with the understanding that when conditions aren't optimal the SL is lower than what's posted. To that end I wouldn't fight a SL of 35 - 45 mph because when I run some calculations that's what I get (being fairly conservative about it too). The problem is I wouldn't expect a SL to fix much. People who know what they're doing run at reasonable speeds for the water and prevailing conditions. People who don't know what they're doing, due to inexperience, inattention, drugs or alcohol, aren't going to be deterred. Moreover they aren't safe even at reasonable speeds. Should we all slow to unreasonable speeds so the drunks can boat safely ? Personally I think you'd get more mileage from a change to the lighting COLREGs or, dare I say it, liscensing with an additional requirement for night boating (kinda like IFR vs VFR ratings for pilots). I'm getting a bit tired of letting a few unforetunate accidents combined with lots of bottom feeder activity dictate what the rest of us reasonable people can do.