I have the HDI skimmer that's going on my TM. It's noticeably larger than your smaller skimmers. Maybe an inch and a half of clearance at each end between the blade cap and the skeg. No room to put anything in front of the transducer for added protection. Is this ducer too big for a TM? It has clearance on all sides...

Not at all, it will work fine on the trolling motor. Lowrance sells a cheap trolling motor mounting adapter for $20 that can be found at basspro or Cabelas. It is made of plastic so it is not the most rugged but can get the job done.

http://www.cabelas.com/product/Lowrance-reg-HDI-Transducer-Trolling-Motor-Mount/1605411.uts

Transducer shield and saver makes a better more rugged bracket for it also.

https://www.transducershieldandsaver.com...-000-10976-001/