I agree now "slicing through it's own bow wave" is an incorrect
impression I got from reading TF Jones. He has built plywood mulithulls
and may have got the impression from watching the point of separation
between the hull and the laminar flow move aft as speed increases.
Michael is right about the left hand and the right hand even when the
left hand does not know what the right hand is doing as may sometimes
be the case.



Michael Daly wrote:


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Vessels do not climb their bow wave - you cannot climb a wave that you create.
That would be like holding a rope up with your left hand and claiming you can
climb it with your right. You cannot push through the bow wave for the same
reason. What happens is that the vessels changes apparent trim angle to match
the wave and you continue pushing the water out of the way. This starts with
_any_ motion of the vessel - it does not start at hull speed. The faster you
go, the more energy it takes.


Yes, now I see it's another mistaken impression from observing the
stern depressed by it's own wave. One shouldn't believe everything one
reads. How many fat-assed boats have been built to increase bouyancy
aft to compensate!

I think I see the correct interpretation now. It's elementary physics.
The force required to push each molecule of water out of the way,
starting at rest and accelerating to some terminal velocity, is

F = MA = MD/T**2 , where M = mass of water molecule, D = distance
pushed

As the boat changes speed neither the mass of the water molecule nor
the distance it gets pushed changes so the force is proportional to he
inverse square of the time in which the water molecule has to get out
of the way of the boat. As the boat slows the time increases and the
required force diminishes, as the boat speeds up the time decreases and
the required force increases.

The total required force is the sum over all the water molecules moved
out of the way which depends on where each is in relation to the hull.
The sum over all the water molecules is the volume of water pushed out
of the way but that also increases and decreases with the boat speed so
the sum includes another time factor. That seems to imply the force
required to push all the water out of the way is a function of the cube
of the boat's speed instead of the square. I just thought of that time
factor on the way over to the public library to type this into the
computer so have not thought it through.

Two long held impressions changed in one afternoon is an interesting
event for which I am grateful to Michael.