I just installed a Humminbird Helix 5 GPS CHIRP SI G2. Like you, I don't fish and don't need all of the extra bells and whistles, but I came across a killer deal on this and jumped on it.
My boat is an 06 Sea Ray 185 Sport and it also came with a Humminbird 600 series depth gauge in the cluster. It has a factory installed THROUGH hull ransducer and was extremely unreliable and useless. I assume something has failed, either the transducer, or the gauge, itself. This is what led me to look for an alternative and I landed on the Helix 5.
The Helix came with a transom transducer and, again, like you, I am not a fan of drilling holes anywhere on my boat. What I did to mount it was to get a piece of 3/4" PVC trim board from my local Lowe's. Cut it to size and used 3M VHB double sided tape to mount the PVC block to the transom. I then screwed the transducer to the PVC block. I did this to test locations and heights before I commit to a permanent mount. I made sure to thouroughly clean both the PVC block and the transon with alcohol and acetone, covered the entire PVC block with the VHB tape, and then let the block sit out in the sun, tape side up, before peeling away the protective film and sticking it onto the transom. Thus us holding on strong. The wire I temporarily secured using zip tie hold downs and double sided tape and routed it through existing path ways, for now.
The Helix, along with its Base Map, is fantastic. Being able to see depth charts live on the screen before I get to them, and verifying them with the actual depth read out from the transducer, is unbelievably useful. I have mine setup to show 3 different depth ranges in various shades of color - Less than 5', 10-20' and over 20'. The screen let's me see any random shallow spots in my path before I actually get to them and it's too late, and the lake I boat on has a ton of those in areas you'd never expect to get shallow. It also has a feature where you can set a depth offset based on the reported lake level in reference to full pool. I'm in TN, and the TVA posts daily what the actual lake level is. For instance, on my lake, normal winter pool is 483.00 feet above mean sea level, and normal summer pool is 490.00 feet above mean sea level. Today it's at 490.42'. Any time the pool is at 490', or above, I leave the Helix offset at zero, unless I know I'm going to try and get somewhere I previously couldn't. If it drops below 490', then I set the offset by the difference and that adjusts all of the Base Map depth chart readouts on the screen accordingly. Very cool. When I first installed the Helix, I went out several times before I installed the transducer, and just the depth chart was enough to keep me out of trouble. Having the transducer now mounted, and seeing the depth readout from it change as I see the boat cross a depth range as I have it setup on the screen match is very reassuring.
Anyway, this is getting really long. My Helix transducer and old 600 series transducer have the same size/shape connector. The difference being that the the Helix transducer has 2-3 extra pins in it for the SI and temp readings. I can physically plug in my old, THROUGH hull transducer if all I wanted was depth and nothing else. There is also a "Y" cable available from Humminbird that allows both transducers to be plugged in at the same time. It breaks out the pins in the connectors and would give you depth readings from your bilge mounted transducer, and everyhting else from the transom mounted one. Some people like this as you can get consistent depth readings at speed from the from the hull transduecer, and clear SI and temp from the transom, while not worrying about mounting the transom transducer in the absolute perfect spot and below the bottom of the hull where it could come in contact with something in the water. This is assuming your old transducer still works and the wiring is OK. You can also replace the transducer.
I am not using my THROUGH hull as it was found to be faulty. The transom transducer is giving me uninterrupted depth readings at anything over about 12-15mph, however, I am having some inconsistencies at slower speed and sometimes when not in motion. My theory is that I have it mounted too close to the starboard side Smart Tab. The Smart Tab lifts up at speed, but retracts back down when I slow down and I believe it is causing turbulence and air pockets at the transducer mounted right next to it. This is why I temped up the mounting with the VHB tape. I will move it away from the tab and test again. When I find the right spot for it, I'll mount it permanently.
The Helix with GPS also tracks my path every time I go out. It leaves a red trace of everywhere I've been that day and makes it easy to quickly figure out my path back to whatever ramp we put in at - I trailer my boat.
Beyond that, it has a ton of other features and settings, mostly relevant to fisherman, but still fun to play around with. Seeing an image of what's below you with the SI is pretty dang cool.
Hope that helps, sorry it got so long. Overall, I highly recommend the Helix series.
