I paddle on a stretch of river where ther is a racing club. They have
the ribver bouyed for racign in lanes. I don't know how they calcuate
the width but I suspect it's wide enough to keep boats from interfering
with each other. Also, the two hulls on a sailing catamaran have to
have open water between them at least 1/3 of the waterline length of
the hulls. If racing without lanes I'd try putting about 1/3 of the
boat length between the boats abeam before making a move to overtake.
Might work.


Over short courses (Olympic ICF class boats) the race is at speeds well in
excess of hull speed - over twice hull speed is routine. That only demonstrates
that hull speed is entirely arbitrary and is nothing resembling a speed limit.

In longer races, that level of power output can't be maintained by mere humans,
so the speeds drop to lower levels.

Mike

Mike is right on. Froude's formula was developed, I believe, for the
British navy (taxes at work) in the days of sail. They were fat heavy
boats with low power. Sailboats need to be fat so the wind doesn't roll
them over. Canoes and kayaks are long, narrow light boats with
proportionally more power. They slice though their own bow wave and
don't sit in their transverse wave. Kayaks are only half as wide as
canoes so they are faster although they are more prone to roll over.
Even more extreme are catamaran hulls and two are needed to keep from
rolling over. I don't know the actual limits to Froude's formula or if
there is an adjusment factor incorporating light displacement and
extreme length-to-beam ratio. When more power was available from
internal combustion engines the British navy did get Nathaniel
Herreshoff to design long narrow light displacemet boats with little
armour or munitions for racing into harbours and dropping torpedoes or
spies and racing out again. Nothing but aircraft could catch them. The
Brits called them Fairmile, the yanks PT (patrol torpedo).

TF Jones in his two books discusses long narrow hulls. He likes to
write about light boats that go fast with low power. All such boats are
notable for their small wakes. They disturb little water as they pass.