U would need to narrow your choices down to either transom or through hull 1st.
There are three choices that I know of. There are three to choose from. In the high speed skimmer type there is a massive 1kw version that would just about tell you what's happening in chinese waters, there is a 50/200khz 600 watt type (my choice) and the baby which is a 83/200khz baby one which aint much chop in dirty and deep water. I don't know much about the through hull types.