Like most recent 34's, our boat came equipped with the Raymarine package which included a DSM 300 depth sounder. We seldom use the full fish-finder screen, instead we've set our E-80 displays to show the depth read-out in small windows along the edge of the screens. This works OK as long as the depth sounder is producing a good reading, but we've had a lot of trouble getting our unit to work properly - particualrly in shallow water.
Discussions with RayMarine Technical Support revealed that the DSM 300 was actually designed as a "fish-finder" - with a range up to 500-feet - it is not really a shallow-water fathometer. After some fussing, we've finally been able to obtain reasonably reliable readings down to about 5 feet, but that's about it.
This spring, we installed a second depth sounder which gives us excellent readings right down to 3 feet. We put the transducer in the starboard hull, so now we actually have readings from each side of the boat. Going down the ICW, this is very cool as we can easily see shoaling as we approach the side of the channel - and of course, this tells us immediately which way to steer for deeper water.
In order to make this work, you need a transducer which works on a different frequency from the Raymarine. We purchased a Furuno RD-30 unit which we mounted on the fly bridge to starboard of the E-80 display. (The new unit operates on 235 kHz and so does not interfere with the 200 kHz operation of the Raymarine). We installed a (retractable) transducer in the starboard hull (under the floorboard in the head ) and we now have simultaneous port and starboard depth readings! Another plus is that we also have water temperature AND speed-through-the-water readings. Although not really necessary, it's fun to know immediately what the current is doing.
Here's a photo of the RD-30 unit in action on Sno' Dog's flying bridge:
The RD-30 unit costs a mere $359 - plus another $220 for the transducer (an Airmar 235DST-PSE). The biggest job was routing the wire from the head up to the flybridge. PDQ does provide built-in wireways, but it's quite a challenge to snake a wire some 20 feet through them.
We are very happy with our latest gadget. Certainly a big catamaran advantage is the ability to have dual depth sounders - it's something I've always wanted!
Henry - Sno' Dog