Remember you're a womble
Currents? The Ray is giving you speed from a paddle wheel (SoW) whereas the Lowrance is GPS speed (SoG). 2-3 kts or more difference between the two is quite common round here. Or if no currents, likely the transducer needs a bit of a service, pop it out (bung in the hole), clean it up, lube it and pop it back in.