Its only a Seawind 24'
Planing is generally when the hull has generated enough lift and is mostly out of the water
Thats a fuzzy definition! So what is it when you are going faster than displacement hull speed but not mostly out of the water?
My Seawind 24 can pull upto 20 knots on a hard reach... there is no way that you can claim that is a "displacement speed" for a 24' boat of any sort. It simply must be generating lift at that speed and therefore riding up on the water to some degree (the amount of spray supports that! oih! she is wet!) That in my book is planing as is surfing, the only difference is the source of the power i.e. Sail vs Sail and Gravity (wave action).
In my book when the boat is displacing less water than its gross weight it is starting to ride up onto the surface of the water. The rest is semantics about degree, which relies on hull form, weight etc etc. Therefore surfing is planing, big heavy monohulls don't do it very well or for very long I grant that and they often need the force of gravity to make it happen (a v big wave) but happen it can. We have had our old Brolga 33 (heavy) planing at 14 knots (well 10 to 14 and back very quickly). You can see the mass of green water she shoves aside as she rides up on it....but alas it scares the poor old girl and she will only do it for 10 seconds at a time and then she wants to turn around and go right back home. You ended up with tiller up round the ears as she falls off her bow wave and the following wave starts to catch her. If you didn't anticipate it, it was ugly, wet, flappy, noisy and the water got very close to the helmsman.... fortunately she was built like a ...... , well nothing I have seen since.
I'm gunna go with Chris White on this one, multihulls plane, very efficiently with minimal fuss but they do it. Thats why I keep talking about sports boats, they plane so easily that it makes the fuss that goes on getting say a J24 up look like a circus. That however does not mean they are not doing it
Have you seen Mr Whites "Hammerhead 54'
" .... now thats a cruising tri ! 20 knots in that