Out of curiousity, what is the project? I'm trying to think of what the data would be useful for and coming up blank.
Best guesses below. Days on the river are really variable year to year though. Figured you'd need some fuzzy data to try and squeeze into a neat formula.
Age: Born before 1990
playboat, ~15-20 days, orange
creekboat, ~5 days, green
12' NRS otter, ~2-3 days oar rigged, ~1-2 days R2, blue
IK NRS bandit, ~0-2 days (loan it out more though), orange
Laser sailboat, ~3-6 days, white
Favorite Class of water: IV