In order to gauge the effect of increasing LWL (or extending a transom) I've made the following graph. Along the left side is time, the right feet. Each step is a half an inch of WL and each half inch adds about 2.1 seconds per hour of racing. That is to say: the extra waterline requires that boat to give 2.1 seconds per half inch to the shortest boat. PHRF at 6 seconds per mile is somewhere between 45 and 60 seconds per hour of racing (average boatspeed of 7 to 10 knots).
The question posed is how much of the increased waterline to include. How much is realistic. We plan to measure a representative sampling in the water at our next race.
