Weed proof, doppler units are now available for a lot of ca$h. I just pull and clean mine before important races. It ties into the ST60 system for VMG calcs.
Do not use petrolium grease on the Oings,,, use silicone grease to prevent from attacking the nitrile Orings..
Interesting experience is that the older DMI paddle wheel is wider than the Raymarine version and works longer between cleanings and works to a slower boat speed.