Oops. That's supposed to say, "The WAVES THE bow makes..." as
corrected below.


--

Roger Long



"Roger Long" wrote in message
...
Question: what could be the cause of the "slowness" of the boat ?

Expectations.

Hull speed is the theoretical limit for any practical amount of
power unless the hull shape is such that planing lift can start to
reduce the displacement. You have far from that amount of power.

The 1.34 figure would also be for a fairly slender (in flow terms,
not necessarily length to beam) hull. The number goes down as the
hull gets fatter. 1.25 is a more typical number for vessels as
heavy as cruising sailboats and heavy power vessels but they will
take a lot of power to get up to it.

If the hull is making the waves and trimming as you describe,
cleaning the bottom and fiddling with the prop probably won't make
much of a difference.

A lot has to do with the flow angles in the run. rebound up and
push the stern ahead, recovering some of the energy expended in
making them and helping keep the stern up. Once the angle between
the run and the direction of motion exceeds 12 - 15 degrees, the
flow separates and the space between the smooth flow and the hull
fills with lazy eddies of water that largely move along with the
hull. Energy from the wave train can not be returned to the hull
through the zone. The effective waterline of your hull is actually
from the bow to the point where the flow lines (generally along the
diagonals) exceeds this critical angle.

--

Roger Long