Very underpowered bayfield sailboat

These engines came with two different gear ratios: 2,21:1 and 2,62:1. Power rating at the shaft (!!) is 7,5 hp @ 3600 rpm, 1 hr, or 6,5 hp @ 3400 rm continous. The 2,62 ratio is the most common in Europe, I think, as it allows a bigger dia prop, but I don't know about Canada. In your shoes, I would:

A/ clean the propeller thoroughly and tell us what dia and pitch you have.
B/ check what gear ratio there is.
C/ check wide open throttle rpm's with a calibrated tacho in flat water, no wind. Note speed achieved.
D/ While the engine is warm, check the no-load maximum rpm's (ie gear in neutral, full throttle for about five seconds).
E/ give us a few pic's of the prop and its aperture.

With a lack of power it pays to check details that normally would not matter, they may make the difference in a bad day.

Edit: added no-load check tip.