Some small local lakes and ponds have only cartop launches and no gas motors allowed. I have a canoe, 10' V bottom and flat bottom and wondered how I could attach and detach a sonar transducer easily without drilling holes. Finally it came to me when I saw a door wreath hanger at a dollar store: (note: click photos to enlarge)
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I cut it to a size that I could bend over the transom or side of my canoe and attached it to a strip of wood:
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At the bottom of the wood strip I screwed in a cross piece for the transducer's wide bracket:
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Zip ties were used to secure the transducer wire and a ratchet lock used to secure the metal bracket at the top:

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If I don't want to use a trolling motor and heavy battery but rather just use oars or a paddle, I use a small 12v tractor or motorcycle battery to power the unit. The location on the boat's transom (pictured) doesn't pick up weeds and the angle of the transducer so it's parallel to the bottom is easily adjusted given the transom angle.