I bought a Humminbird PiranhaMax Portable fish finder for my kayak. It has a suction cup transducer. It can supposedly shoot through the bottom of the kayak, but I've only tried it attached to the outside so far and it seems to work pretty nicely. A lot of the reviews on it are that it doesn't find fish. I can vouch that it didn't pick up very many fish, but it showed me the contours of the bottom and any structure, which is what I bought it for. It comes with a rechargeable battery and a carrying case.