You can not replace the paddle wheel, you need a whole transducer. You can get them at Pyacht.com or visit ComNav.com to find a different dealer.
I would consider upgrading from Nexus to NX2. You would need to replace depth and speed transducers, the server and add/replace on NX2 multi display. You will get more functionality, more NEMA ports and a USB port and can use the FX2 software on your computer for beetter calibration and to compute polars and analyse your race data.
The NX2 systems use the same transducers as virtually all other instruments sets out there instead of the proprietary ones used in Nexus. The Nexus transducers are more expensive and less reliable.
