You're sailing a dinghy with a smaller mast that sees a very small difference between the angles and strenght of winds aloft and
winds at the water level. In fact with that mast height, they are almost negligenciable.
Just rig your boat, as you normally do, stand up near the shroud, raise your arm and install on each side, at the height of your finger tips, a silk strip
of cloth as shown bellow on both shrouds. You can even get a green and a red one for port and starbord.
That is the best option for your boat, and believe me I have had my good share of dinghies!! Sailed a few, ehehehehe
Even today, sailing on larger boats, that is what I use, I use them more often than ST60's, windexes and mast indicators (in fact my windex disapeared mysteriously lately) and all the other fancy crap...the silk strips are inexpensive, they are also at my eye level forward of the helm, thus the efort made to look at the wind indication is minimal, and I get not distracted.
With time, you will learn to look at them, and evaluate the wind strenght by the way they are flaping and moving.
On some boats, the leeward one can actually tell you how the Genoa/main wind slot is behaving...a good thing.
West Marine sells a pair of wind indicators mounted on a wire that coils around the shroud.. (see here)
I like them, but they get damaged with use. SILK IS THE TICKET, cheap and just tape it to the shroud or use a clamp, like I do. Also bought this one at Westmarine, but clothes pegs will also do the trick, as you can remove them upon removing mast. I used clothes pegs for over 20 years.
As far as weatherhem and leehelm, in your case and for the wind speeds you mention, its just a question of main trim. Dont worry with rake and the rest...you are simply either undertrimming or overtriming your sail. Outhaul, boomjack, main sheet are your tools, learn how to increase bag and curvature in your sail, how to twist the raoch, etc.... Move them, pull here and there and learn on your own...that is the fun part of it. Your not triming right, that is all.
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