The Garmin transducer provided is 'in hull' and, while there is no temp, it's not a bad product. For a very low price, you get a decent sonar image and no fouling since it does not touch water.
That said, it's totally inadequate for the type of ocean fishing that I do. I talked with my electronics guru about lots of options and decided to install an Airmar T80 temp sensor to solve the immediate problem while I researched other options. There are many considerations for different conditions and use cases, but, important to me:
- The transducer needs clean water to site thru making the forward position, where the GT-15 is located, the best position. If you mount further back or on the transducer you will likely have turbulence affecting the view. I have outboards to work around.
- According to Shane, whom I've know for years and trust, you won't get a dramatically better view unless you have a 1kW transducer. He's been a Garmin dealer for a very long time and knows all the products extremely well. He said the GT-15 is not that bad and to beat it you'll need a lot of power.
- The GT51M transducer pair has been installed by some folks in the Tugnuts community and I looked at that. It's the most reliable way to get side view. However, since I boat in the ocean, I don't like getting near anything that resembles a bank or shore where side view comes into play;-) Hence, I'll be getting a single 1kW transducer on the next haulout and, hopefully, get it wired so I have my current gear, GT-15 and temp sensor, as back up.
One other note is that Shane said the temp sensor took him 3 hours to install on my Cutwater due to all the wiring and blockages and that on a 'normal' boat, it takes him less than one hour.