Morgageddon tries to remember college...

*Well, it's worded awkwardly, but I have to assume you go from 3 m/s at the start of your 500m and then end at 16 m/s at the end of the 500m. From this, you can make a velocity profile, use the standard kinematic equation and integrate to find the total energy expended to have the sailboat go from 3 m/s to 16 m/s over 500 meters. Then, you can equate that to an equal force applied at a single point at the start, with a magnitude and a direction, something that'll be like 1500N @ 73 degrees north of east (since you said nothing about currents or other forces acting on the sail boat). *

tl;dr

Draw out the problem to start. Find your governing equations. Solve said equations.