The depthfinder on our older Four Winns has been giving us eronious reading and I'm thinking of replacing it with an inexpensive fish finder rather than a new depth finder. Our boating is all on lakes which all seem to have a number of shallow rocks. How well does a fishfinder work as a depth finder?

A fish finder can function as a depth finder. What fish finder are you looking at?

I'm really happy with my Hummingbird 610 depth-meter. Works great, and actually DOES keep reading untill at least 60MPH. This year will be year 3.

Seems very accurate every time I have checked it (in shallows).

Epoxied mine inside the lowest part of my hull, right next to the jet pump intake, R/H side, looking thru the 'glass.

I highly recommend the Navman 4380 fishfinder. About $225 online, and for $140 more you can add a fuel flow meter to it that give you all kinds of info, including mpg, gph, range and gallons remaining.

It also has an integrated speedometer, water temp sensor, voltmeter, sonar and mileage log, and with the connection accessory can interface with SmartCraft Merc sensors.

I was thinking of something pretty basic like the Hummingbird Piranha Max series.

Keep in mind that NO depth finder or fish finder will show you a shallow rock. They will show what's directly below the boat so just about the time your lower unit finds the shallow rock your depth finder will show you it's there.

I chose a $100 depth/fishfinder over a $100 dial depthfinder.
The options and window were nice on the fishfinder vs. just numbers on the death gauge.

My Humminbird Piranha Max 15 install two years ago: Link

Yup, the lower unit is much more accurate at locating submerged objects than the depth finder is. Gets your attention much quicker as well.

You would know!!

I love my Humminbird 717. It was less then $200 and uses NMEA 0183 for communicating with my GPS and other devices.

Humminbird 717

I had a Cuda 240 on the Monty. It was nice as it had GPS, water temp and depth all in one.

Since you are replacing, go with a fishfinder.