Billy, from recollection it is a DST200.  I have not experienced any problems with that transducer (Bill, this is the depth, not the speed transducer).  But the man who would know is Stephane Geniteau, the Amel guy at Pochon.  Pochon installed all electronics on Amel 55s and Stephane did the owner training.   I've found him very responsive.   stephane@....  Good luck.   

Joerg Esdorn
A55 #53, Kincsem
On the hard in Vigo