I read this article on the most recent Practical Sailor where they
discussed wires slapping inside the mast. Strangely, this has never
bothered me although I bet it does now (cancel my subscription before
they make me aware of more things to be bothered by). So....Useless
idea #3436

Wireless mastop anemometer

A simple anemometer cup that turns a bar code like reflective wheel on
top of the mast. This wheel would be very lightweight (ounces) and
about 6" in diameter. it could also be arranged to show wind
direction and wind speed. On deck, next to one of the shrouds is a
little penlight diode laser/receiver shining up toward it. The laser
is of course modulated with a sin wave so the reciever can use a
lock-in amp to see the signal in any noise and it reads the bar code
like reflector. Sails dont block it cuz its inside the shrouds.