Displacement & Design Waterline Displacement should be* the same.
Displacement is the weight of water
equivalent to the immersed volume of the hull
Design Waterline should be* calculated to include the total amount of weight the boat was designed to carry, hence Displacement at the Design Waterline should* include the combined weight of the boat, occupants, and the cargo & gear
* Design Waterline (Displacement) can be a some what arbitrary number, manipulated by some manufacturers to only include half-full tankage, and other light ship conditions.
Ted Brewer Presents A Primer on Yacht Design (The Numbers)
Ted Brewer Yacht Design
Sailboat Design Ratios ~ by Dan Pfeiffer
Essential Design Data ~ by Michael Kasten
Essential Design Data
Carl’s Sail Calculator ~ by Carl Adler
Sail Calculator Pro v2.72