Parallax wrote:

.....I would really like a
knotmeter that will help me really tell when my sail trimming is
helping (I admit, I really can't tell most of the time) ....

Any better ideas?

Yes. Hop into a high performance racing type dinghy like a 505 or a
Johnson 18. After you learn to *really* sail, you won't need a knotmeter
to tell when your sail trim is good.

Fresh Breezes- Doug King