The results and the chart plot are based on an
SL Ratio of 1.34 this “magical” 1.34 is just a guide as to the
usual theoretical hull speed, beyond which the increasing amount of power required
to push a hull past a certain speed becomes impractical. 1.34 is typical but lighter
displacement boats may be allowed a higher number. Note that this number only applies
to displacement hulls. Hull speed, as
calculated here, is important as it is a building block to attaining figures like,
what power is required and ultimately calculating what propeller may be optimum
for a particular boat.
The chart displays speed at different percentages of theoretical hull speed. Typically
you will not try to push a displacement the vessel past 100% of hull speed but I
have shown the it at 125% so that in the next step it can be used to illustrate
how much power is required to push the hull past this speed.