re: Just bought my first boat...preowned

Congrats on getting a PRE-OWNED boat...the only way to go.

Hull or transom. Transom is easiest and most common. Usually works just fine. However, some hull designs simply give problems (unique curvature lines), but some sort of tweaking will usually fix it. However, occasionally it won't. I had one of those problem children about 20 years ago. Finally just had to mount inside the hull...problem solved

Military small boats have hull mounted transducers.

I would try tweaking it like the previous OBers suggested. Only if that fails would I hull mount it.