Transducer
I have a Lowrance X85 and before I bought it I contacted them on the web. Their reply was to go with the 20 degree transducer in water up to 200 ft.
Contact them and see if the reply is the same-it was 2yrs. ago. Hope this helps.
P.S. You must remember, in shallower waters, you will be seeing very little with an 8 degree transducer!