Hi Talador,

The speed of 1.34 times root LWL is not the maximum speed for a displacement hull, it is the speed at which the wave produced is equal to waterline length. Beyond this speed the vessel tends to squat  (trims down by the stern) and the power curve rises steeply for hulls which are optimised for lower speeds – classic displacement hulls, very economical at lower speeds, very uneconomical at higher speeds. Nevertheless, by application of enough power, even  a hull very poorly suited to higher speeds can be forced to go faster than the so-called hull speed.  Hulls may be designed for better economy at higher speeds  in several ways. Slender hulls is one way, planing is another. Slender hulls moving at speeds considerably higher than 1.34 root LWL may do so without being lifted above the static elevation, and thus do this without any significant planing taking place, ie. They are travelling in displacement mode, at speeds at which a wider, shorter hull of suitable form would be planing. The speed of these slender displacement hulls is not ‘limited’ by 1.34 root LWL.

You may find a more technically precise definition of planning in a text on naval architecture, but the gist is close enough for the layperson. Over the top being the relevant part. This happens when the hull is lifted above the static level. More lifted => more planing.

Regarding the actual power required for a round bottomed proa travelling at speeds considerably above 1.34 root LWL, I suggest you accept Rick’s calculations, he has quite a lot of experience with easily driven hulls of this type.

Cheers,

Peter