Lighter boats that are able to plane will definitely be able to more easily and more frequently exceed their hull speed, but that doesn't make the hull speed calculation any less true as a good "rule of thumb" calculation.
I have a good friend with a Catalina 25, which on paper is almost the same boat as my Hunter 27 (waterline is almost identical, displacement is almost identical, sail area @ 110% genoa is almost identical, he draws 6" more than me, but I think his keel is roughly the same length as mine below the hull) and I can sail circles around him most of the time (one night sail when we were both out in really light air, I actually did sail in a circle around him
, he wasn't impressed...)
Why is my boat so much faster than his? Sure some of it is probably the skipper :dance:, but the shape of my hull is different. My hull is very flat on the bottom, where his more round.
I have also had his boat up above 7kts many times, even close hauled, but it's usually because of unusual circumstances such as when double reefed in 25kt winds... In most average circumstances, he still never exceeds 6.1/6.2kts...
So Yes, given the right conditions our club cruiser / racers (like most Catalinas, Hunters, and Beneteau's, what the majority of people on this board have), will be limited to the hull speed when sailing in average conditions. Those with race hulls specifically designed to exceed thee average hull speed are clearly except from this discussion.