Just bought hds7 for the bow, along with a TMB-S bracket for the trolling motor. I am wondering how well this bracket works, as there is no star, or grooved washer to hold the skimmer in place, as there is on the transom bracket and kit that Lowrance provides...

You are just installing a breakage waiting to happen.

If you want to use a transom transducer on a trolling motor you should use some type of protective mount like the Transducer Shield and Saver.

Otherwise you should use a transducer that is designed for trolling motor mounting (the puck style).

It's just $40 for the proper transducer bracket.