the transducer that came with my Mark 4 lowrance works great. it reads bottom at full throttle
it's mounted on the transom with about 1/4" sticking below the bottom of the hull. it shoots a good rooster tail but it works great!
thru-hull & in-hull are the other types. to me, they're named by the way they mount, not the way the operate.
thru-hull i consider to be the one you drill a hole through the bottom of the boat for, i'd never use one of these because i don't want any holes in the bottom of my hull to have to maintain. i don't mind a little screw hole in the transom though.
in-hull i consider to be the puck style that actually shoot thru the hull (confusing right?), you just glue em inside the hull, typically in the bilge area. there's a few ways to find the sweet spot. the most effective being to put a big glob of vaseline on the puck between it & the hull. go out & test it on the water. mark location, clean & glue it in. as previously mentioned, any air bubbles will ruin the reading. some hulls have air bubbles in the glassing, & if you have air bubbles in the glue, that also ruins it. those don't read as good as a transducer actually in the water column
they can read very close & almost exactly as good, but you do lose a little bit through the fiberglass. not enough to matter typically, but some nonetheless. if you want to drill no holes, you need the in-hull puck style that shoots through your hull
the best bet for installing a transom mount, is to get a piece of cutting board or starboard or something that won't rot, & screw that to your transom. then mount your transducer to it, that way if you have to drill 6 holes to get the right height or move it further right because of air from the prop screwing up your depth reading, you drilled 6 holes in the board & not the boat. swap out the board if the extra holes are a cosmetic bother
to get the right height on a transom mount, you want it as low as you can get it, but the lower you go, the bigger the rooster tail it's gonna shoot. and if you get too close to the prop, it's going to put air in the way & ruin the reading
you want it mounted on the right side of the boat at the lowest point but not within 8" of the prop, & preferably 12" or more away for a standard rotation engine (clockwise). this can be a problem getting the boat to read bottom at full speed on certain hull designs. that's why it's good to put a big board on there to play with mounting location
the closer to the prop, the more likely it's going to be screwey at speed from the air created by the prop spinning. if your transom on the bottom of the hull has a real steep angle, this means your depth reading may be off by a significant amount when inches matter. conversely, if you get too far from the prop, the transducer might not be in the water at full throttle....you have to find a balance between too close & too far away from the prop for the particular hull design.
you do NOT want to mount it in front of ANYTHING that causes turbulence, for example strakes or chines in the hull, pickups for baitwell etc... & that is true regardless of which type of transducer you use, whether it be in-hull, thru-hull, or transom mounted.
if this sounds confusing, it's not, just stick it on there, it will read fine lol
