Ted 33,

Welcome to the confusing world of modern sonar and navigation electronics. Since your Garmin units appear to be at least 15-20 years old, compared to contemporary units (say within the last 5 years) they are near "dinosaurs". If you want to upgrade, you need to consider things such as the cable connecting type (number of pins and design), thru hull hole size and type (some newer models of sonar have different thru hull mounting designs), and whether a newer unit requires a separate "black box".

Also, when you say looking for fish at speed, what speed? Some transducers are better at returning clearer marks at higher speed than others. In Lake Erie, especially in the Western Basin, having the ability to see out to the side of the boat is important, because in the shallower water fish tend to scatter away from a boat, especially at higher speeds. As for an in hull or transom mount transducer, it depends on your boat. You have an outboard motor, so a transom mount should would work as well as a thru hull (which you already have). Check with the boat manufacturer as to which type transducer they recommend for your boat.

Sonar and navigation units have come a long way in 15 years. Yes, the "target separation" (being able to pick out / separate fish from other sonar returns) is much better in the modern units. However, you need to truly understand how to use any fish finder in order to get the most out of it.

Another option you have is to get a unit and use a pole mount transducer for perch fishing. Once you anchor, you can deploy the pole transducer to scan for perch schools.

I would give more advice, but I'm not familiar with your particular units. I am in the process of replacing an old Lowrance Eagle unit that is at least 20 years old. Finding information on it so far has been mostly unsuccessful. I would contact Garmin and ask them, but be prepared for this to take several communications and a few weeks to get all the info they may have. It took me a long time to research and get all the information I needed from Garmin for my new Garmin Livescope unit, including the mobile system I am building.

Good luck, and stay on them. Eventually you should be able to find a Garmin tech that can answer your questions.

You might also try contacting a Garmin rep, or an outfit such as Boat Things in Columbus that specializes in installing sonar and navigation equipment on boats. There is a lack of both of these around the Port Clinton / Sandusky area.

Boat Things (click it) - Boat Things