At the risk of perpetuating another freewheeling-v-fixed controversy I submit the following ( rather lengthy ) quotes as I only read 'em and repeat 'em
From Practical Sailor
The late Carl Alberg designed the 35 as a coastal cruiser. With LOA of 34’9" she has a short waterline of 24’0" and moderate beam of 9’8" good proportions for slipping along in light air.
The waterline lengthens when the hull heels, and the boat foots nicely in a breeze.
. . .
For this he drew a 37-foot yawl. It compares to the 35 as does a thoroughbred to a Shetland pony, both from a good stable. The Alberg 37 raced
under the CCA rule and the design has long overhangs and a short full keel ending with a raked rudder to reduce the wetted area. Showing the typical Alberg moderation of basic ratios, a slim, slippery hull
From Ted Brewer's Primer on Yacht Design
DISPLACEMENT/LENGTH RATIO: The D/L ratio is a non-dimensional figure derived from the displacement in tons (of 2240 lbs) divided by .01 LWL cubed, or, Dt/(.01 LWL)3. It allows us to compare the displacement of boats of widely different LWLs. Some examples of various D/L ratios follow, but are generalities only as there is often a wide range within each type.
BOAT TYPE D/L RATIO
Light racing multihull 40-50
Ultra light ocean racer 60-100
Very light ocean racer 100-150
Light cruiser/racer 150-200
Light cruising auxiliary 200-250
Average cruising auxiliary 250-300
Heavy cruising auxiliary 300-350
Very heavy cruising auxiliary 350-400
STORM, a wonderful 27' LWL sloop on which I raced with Bill Luders many years ago, had a D/L ratio of 386 so she would be considered very heavy by today's standards. However STORM was 39' LOA
and when she heeled to a breeze her long ends would increase her sailing LWL, thus reducing her D/L ratio to a more reasonable figure when we were beating to windward. If she picked up 3 feet of WL her D/L ratio dropped to about 281, a significant change, and one that made her a very competitive racer in the 1960s.
Rodney Johnstone of J Boats
Where does performance come from? Length is most important.
Average speed in knots for the typical sailboat is roughly equivalent to the square root of its waterline length. Hence a boat with a 36-foot waterline length should sail at about 6 knots under "cruising canvas"; a performance-cruiser should be able to exceed this pace in all but very light winds.
the Boatbuilding Community
HSPD = Hull Speed (top)
HSPD = SQRT(LWL)*1.34
This is the theoretical hull speed for a displacement hull (like most sail boats). It is a function of the length of the wave created by the boat as it moves through the water. Wave speed is a function of wavelength, longer wavelength is faster. Longer boats make longer waves. Since longer waves are faster boats that make longer waves are faster [Garrett]. The hull speed may not be as precise a figure as the formula leads you to believe (1.34 sounds pretty precise doesn't it?).
LWL is not static. As the boat heels it can increase. Older racing boats with long overhangs used this to get some extra un-measured LWL to beat the rating rules of the day. As the boat goes faster the bow and stern are immersed deeper in the wave made by the boat. This also increases waterline. In the 19th century sailing ship speeds were often expressed with a hull speed factor. A ship might have a speed factor of 1.17, meaning it can make a speed of 1.17 x sqrt(lwl) [Chapelle]. There are conditions where you can exceed the theoretical hull speed. Surfing down a wave for example. I have had my boat (LWL=21.6 feet, HSPD=6.25) surfing at 10 knots on waves.
When surfing or planing the hull is not in a displacement mode. So hull speed may be a bit of a moving target.
Let the thread freewheel to find a fixed answer !