Portable fish finder

[Jonathan]

I am considering buying a portable fish finder to use whilst trolling. The reason why I would prefer a portable one is because I am usually out on different boats. Has anyone tried portable fish-finders whilst trolling - are they any good & do they give good readings or does the moving water disturb them?  Does anyone have any recommendations to make or things to look out for?

[skip]

I don't think you can use a portable finder for trolling in the manner in which you are describing with great effect. Perhaps for very slow trolling but I can't see how it would stay down over 4 knots?

Your only option is a transom mounted transducer as opposed to through-hull, that's as portable as you're going to get. I believe Gottie uses/used one.

[Jonathan]

Some manufacturers are offering what are known as suction cup transducers where basically the transducer can be temporarily stuck to the transom of the boat (as long as its fibreglass I was told) using a very simple rubber sucker perhaps 5 inches diameter.

However I am not sure about how reliable the effect of the suction cup would be or whether it would get undone at speed or become hard and useless with age. And I am also a bit unsure about the effect of the turbulence at the stern of the boat.