Actually, the water does not move forward in a wave but you are right
that the surfing examples are irrelevant examples since the waves are
pushing the boat forward in other ways.

The speed length ratio of the Newport 33 at 7 knots would be 1.35,
just a hair above the generally accepted displacement hull maximum of
1.33. If the hull has an easy run, the counter becomes part of the
waterline length as the stern waves rise up under it. Adding a foot
brings the ratio down to 1.32, exactly what you would expect for an
easy hull like that one.

--

Roger Long



"Stephen Trapani" wrote in message
...
Rolf wrote:

I own a Newport 33 which has a waterline length of 27 ft.
According to
the formula, the theoretical speed for the boat is 6.96 knots.
I have a 16 HP diesel with a 2 bladed impeller, and a maximum
engine
RPM of 3300 RPM. Running the engine at 2700 RPM I can readily reach
6.5
knots.
In a good wind I can go to 7 knots. The maximum speed I have ever
done
was 11 knots on the GPS surfing down a wave with full sails up on a
very broad reach in about 30 knot wind. Many other boats of the
same
design ( relatively light displacemnt, fin keel and spade rudder)
report he same thing.
Racing boats in the around-the world alone race routinely exceeded
hull
speed for long periods surfing down waves. The hull speed for a 60
ft
boat is 10.4 knots andthey were achieving more than 20 knots I seem
to
remember. So that is the way to go faster than hull speed, find a
wave
and then surf down.
Catamarans also go faster than hull speed all the time. So if you
put
enough power into the boat in relation to the displacement and
wetted
surface, you can exceed the Hull speed.

I think that traditional full keel boat with a high displacement
would
have a lot of trouble getting close to Hull speed.
Rolf

Hull speed is the absolute maximum that boat can travel through
water. All your examples have the water moving forward also so the
boat is not exceeding hull speed through the water.

Stephen