Rich,
I recently purchased the 587 Furuno and contacted Furuno on recommendations for a transducer. Furuno put me in contact with their Great LLakes region representative. He highly recommended the 525TID-TMD Transducer. It is a transom mount which I like because I can tilt it (if needed) to see my rigger weights. I bought it from BOE Marine.
http://www.boemarine.com/furuno-525tid-tmd-tm-transducer-w-temp-1kw-10-pin/
Brian