Catching garfish from boat is not a problem, since you can fish for them in exactly the same manner as you do from the shore, using float, fly or spinning tackle (set up as per a flying collar rig but with a sliver of mackerel strip instead of a lure.) However if you want to concentrate on other species, catching garfish almost by accident, as it were, then you might like to experiment with a home-made boom that incorporates a flounder float.
This can be fished directly over the top of standard leger tackle and enables you to carry on targeting other species such as bass or plaice.
To make the boom you have to twist the wire into the shape shown on the diagram. Then, to fish it, you simply attach a short trace and slip it onto the main line, behind a bead, before you tie on the leger underneath.
Once this is complete, then you will need to tie on a sliding stop knot and then set this to the depth off the bottom that you want the tackle to fish.
When you get a bite it will feel really peculiar. The line will be bouncing around so that you can feel the fish, but there will be no weight on the rod until the weight has caught up with the boom. Then you will feel it!
Close up of the 'boom'.