What is Velocity Ratio (VR)

What is Velocity Ratio (VR)?
The Velocity Ratio is attempt to estimate the velocity of a given sail boat.
The VR for a good relatively fast boat will be about 1.0. A full-blown race boat will be in the range 1.5 to 1.8.

How to calculate the Velocity Ratio (VR)?
Velocity Ratio = 1.88*lwl^.5*sail area^.33/disp^.25 / (1.34*lwl^.5)
Sail Velocity Ratio formula
Velocity Ratio formula

lwlftLength of the boat in the waterline
SAft2Sail Area
DisplacementlbsDisplacement of the boat in pounds

Problems with the formula?
The main problem with the formula is that "sail area" and "displacement" are not clearly defined. This means that the SA/D calculation may result in different values for the same boat.
Sail area:
Which sails is the calculation based on?
- mainsail and fok?
- mailsail and genoa? And if 'yes', which genoa?
- Is it the displacement for an empty boat?
- Is the motor included and what about the fuel?
- Are the weight of the crew included?
- What about water, food and the like?

In our reviews - when comparing boat types - we have decided to use the nominal sail area as defined in the ISO 8666 [1] standard, where the sail area is defined as (P*E + I*J)/2. where: