Thru Hull vs Transom Mounted Transducer GT-51 for 8412

G'day all,

I am about to get a 6.5m fibreglass boat fitted out and I am wanted to fit a Garmin 8412. I have heard some good things about thru-hull transducers and was wondering if it was worth going for. I am looking at the GT-51 (both available in transom mounted and thru-hull). The boat builder has told be that he can access the hull via the kill pen, and I am after thoughts (pros and cons) of thru-hull vs transom mounted. Curious if there are any considerations seeing as though the hull will need to be cut/drilled. I have actually never seen one in person, nor do I know anybody who has one.

Thanks guys.

There can be a lot to consider with this. Not all hulls do well with a staright-out thru-hull mount. They can be prone to poor pictures at even moderate speed. I fitted a B175M Airmar to the Reefrunner, picture is poor at any sort of speed. I had very little latitude with mounting position due to the tank and rear bilge arrangement, but I made sure it was not in line with one of the strakes. This is touted as a must. The Caribbean hull has short strakes, I placed it between two of them, thinking I was doing the right thing, and probably just exposed it to the bubble stream from both of them as it fans out . :-[. I have since bought a hull spacer, made by an Australian company, for the big Airmar which is meant to help by getting the transducer 10mm further off the hull, theory is that you just need to get out of the very thin layer of turbulence that exists at any interface between hull and water, on any hull. Have yet to fit it. I helped out mate fit a TM265 to an old platey last year--it gives a brilliant picture at 25 knots.>:( And with a TM, you have a degree of adjustability not available with any other installation.
A faired transducer, where you are dropping it well down into largely clear water is usually the best for a good clear picture at speed, but this can interfere with your trailer., and will cost speed and fuel--I've seen them cost a fast hull a full 4 knots.
Wet-boxing, where you mount the transducer inside the hull, in a bed of silicon or a box actually filled with a liquid, can work, but you have to remember you are
a) asking the transducer to shoot a signal through up to 25mm of fibreglass, with resultant loss of power
b) And the signal still has to content with any bubbles running along under the hull, as above.


What hull are you buying, exciting times.

OK, big edit time, I should've looked at the transducer you are proposing first So the thru-hull version of the GT-51 comes with a fairing block, and looks like it needs to be keel mounted.. There doesn't appear to be an option for a tilted angle version, made for correcting the vee-angle if you mount it either side of the keel. So you would need a spacer block cut at an angle to correct for the deadrise angle, unless you want to mount it in the keel. Not hard to get done, probably. Downside to a keel mount is that it is very vulnerable to grounding, and may also interfere with you trailer, unless the boat overhangs the rearmost roller/skid by enough. For a 600w transducer, I don't know if I would go to the trouble.. I have the equivilent sort of Raymarine transducer , does the downscan/sidescan/basic sonar thing, Mounted on the transom, works fine.

Thanks heaps for that, a lot of insight. I am actually starting to lean towards a transom mounted unit. I believe that a TH may cop a bit from the trailer, and that the keel may no longer be accessible and I would have to look at twins. Probably more effort than it's worth. Thanks again.

Would depend on the hull. What hull are you looking to buy?

Have a GT 51 on a Yalta 2200 tramsom mount work fine , good transducer I run it and a TM 260 (1KW) from the same head unit and the GT 51 punched above it's weight.

Transom mount has the advantage of being easy to fine tune the transducer position ... both up and down and horzontially until you get the perfect return , that hard to do with a thru hull.

BigE

I have a Garmin 75dv in my seafarer with a Airmar B60 thru-hull transducer and it works brilliantly and as good at speed. Just letting you know my experience with thru-hull transducer. Good luck with your final choice


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It seems increasingly common for GT51's to just get sikka'd to the bottom of the hull. Especially for boats with planing planks.