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Depth, GPS Transom Transducer Question

Gmilburn

Member III
Hi all,

With the risk of offending the purists, I need to replace the stock depth finder on my 1977 E-29, and am considering a Garmin or Humminbird Fishfinder. They are now quite common and have built in functions such as Depth, Water Temp (I dont really care about that), Speed (via GPS) and chart maps. Since I sail in an inland lake, Im most interested in not running aground as the water level fluctuates over the summer (there are numerous submerged sandbars lurking just a few feet under the surface). My idea is to install a combo unit for less than $1000.

I really do NOT want to install a thru-hull transducer and have read about installing one inside the hull either directly with silicone or via a mineral oil sleave to keep the soundings clear thru the hull. I see that transom mounted transducers come with most units at no extra charge, but thru hull transducers can cost as much as $300 extra.

My Question is do I need to pay extra to get a real thru-hull, even though I want to mount it on the inside of the hull, or alternatively, what about the stock transom mounted transducer, can it be mounted on the back transom and still function with the normal "heeling" of a sailboat, or can it be mounted adjacent to the hull using silicone or with a mineral oil sleave.

Anyones thought or experiences would be greatly appreciated.

Thanks so much!
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Funny you should bring this type of project up........
I am in the last stages of installing a Garmin in-hull DS transducer and data module (GSD 21) to feed depth info to my Garmin chartplotter (model 3005c).

The AirMar transducer mounting kit has a "cup" that needs to be glued to the hull surface and has a way to orient the puck to face the transmitting surface straight down in spite of some deadrise to the hull.

I hope to have it doing something useful in a week or so.

Interesting project, if you don't mind working with #22 wiring while laying on your back under the cockpit.

And, yes, the transducer is being installed under the cockpit in the rear part of the hull. (In theory having it forward would give me a nano-second more warning of a grounding, but at 6 kts it's not a major concern where we sail.) It is also a lot easier to mount it parallel to the water surface in a flatter part of the boat...

As to whether you get a better signal return shooting through the hull or with an external transducer, I have had both types on different boats. Getting the signal somewhat attenuated by shooting the pulses thru the laminate seemed to reduce the theoretical return from about 360' to around 200' on a Standard Horizon I installed that way on a prior boat. Eliminating one more hole in the hull is not a bad trade-off, however. "Everything's a compromise."

:)

Cheers,
LB
 
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SASSY

Member II
Transducer

I have a garmin 540s with transducer. It can be epoxyed on the inside of the hull (as long as the hull is not cored). I have never used it, and would prefer the lowrance HDS7. I am asking $550.00 if you are interested.
Thanks
 

G Kiba

Sustaining Member
Depth Meter

I sail on the Sacramento Delta - lots of sandbars and places to run aground.
I bought a $100 dollar shoot-thru-the-hull unit and have found it quite adequate and accurate enough for my needs. The unit reads out depths that correspond with the chart depths on my GPS (with tide considered). Needless to say, I'm glad to have spent money on sails and fun stuff.

I know exactly when I run aground - the boat stops :)

Grant Kiba
'73 E27
Antioch, CA
 
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dwigle

Member III
When I bought my first monohull, a Columbia 26, it came with an uninstalled Humminbird with a transom mount. The instructions indicated it would be ok to epoxy the transducer to the inside of the hull, but it should be near the transom. I mounted it next to the engine well and it worked ok except on starboard tack when it pulled out of the water, or when we were motoring and the transom mounted outboard somehow affected the signal causing it to not work.

I later found a transducer in a clearance sale and mounted it ahead of the keel and had no more problems. Make sure to use enough epoxy so there no gaps or air bubbles.

Don Wigle
Wiggle Room
E38 #8
 
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