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Old 18 November 2018, 16:42   #1
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Depth Transducer Fitting - what do we know?

So in my rebuild I am wanting to fit a depth gauge.

I have bought a Lowrance hook 4 as it gives me GPS speed/location and depth, not interested in finding fish.

The transducer can be mounted on the exterior of the transom (messy, vunable and ugly) or it can be fitted to the inside of the hull.

The instructions say bed it in epoxy, I have heard before to bed it in silicone, which is best? Any other help/advice much appreciated.

Much obliged.

Ribtecer
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Old 18 November 2018, 17:31   #2
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In this part of the world almost all boats have them fitted externally, even comercial fishing charters who's boats are permanently moored on the water.

Mine is also externally mounted as I've done for around forty years. My Lowrance picks up bottom with a standard 200/50khz in depths deeper than 500m. It holds bottom ok on 200khz even at speeds of 40kmh.

There are pads that can be stuck to the stern of a hull which tranducers can be fixed to, to save drilling into the hull, though I don't worry and drill into my boats.

What I like about the externals mounts is the fact the beam shoots straight through water and not the hull that could possibly have the odd air bubbles in the fibreglass which greatly reduce performance. An external mount also allows for adjustments and tweaking after each water test. Slightly angling the back of the transducer lower than the front helps with holding bottom at speed. If you permanently fix it in the hull it can be messy and difficult to fine tune.

In saying all of that for shallow water work you don't have to be that precise in the setup.
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Old 19 November 2018, 05:01   #3
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Hi Ribtecer, were just sorting our depth now. For a couple of years we had our depth mounted externally on the transom. We tried everything , port side,starboard, clear water, angled it up/down and it always lost signal at 20knots. You couldn't rely on it.It is a Garmin system.
I had a spare Garmin thro hull P79 transducer. Last weekend we put in the bilge and flooded it with water. The transducer wasn't even correctly mounted. it was just lying there sloshing around. The signal and readings were rock solid and spot on!!! We were very impressed. Garmin instructions say to put the thro hull in a bag of water and test its position before you glass it in. I'd do that first. Incidentally most Transducers are made by Airmar.
Hope this helps. Nik
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Old 19 November 2018, 05:48   #4
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I've used two methods that have been successful in the past.

First was...build a well using plasticine or some other such material, fill well sikaflex or similar, bed transducer into sikaflex. You just have to be careful that no bubbles are introduced when you fill the well with your chosen.

My favourite was to get a short length of drain pipe with a screw on cap on one end.
Bond the open end inside the hull at lowest point (You may have to shape the drain pipe end to get a reasonable fit. ) Drill a small hole in the end cap for the transducer cable to fit through. Fill drain pipe with oil, place transducer inside and screw cap on securely.
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Old 20 November 2018, 03:42   #5
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Quote:
Originally Posted by matata View Post
Hi Ribtecer, were just sorting our depth now. For a couple of years we had our depth mounted externally on the transom. We tried everything , port side,starboard, clear water, angled it up/down and it always lost signal at 20knots. You couldn't rely on it.It is a Garmin system.
I had a spare Garmin thro hull P79 transducer. Last weekend we put in the bilge and flooded it with water. The transducer wasn't even correctly mounted. it was just lying there sloshing around. The signal and readings were rock solid and spot on!!! We were very impressed. Garmin instructions say to put the thro hull in a bag of water and test its position before you glass it in. I'd do that first. Incidentally most Transducers are made by Airmar.
Hope this helps. Nik
Interesting. Mine is externally mounted and works perfectly. Its a Garmin GT52 Transducer with Garmin 95SV.

The only problem I have had is occasionally the plotter reports that it does not recognise the transducer, but that is down to corrosion on the connector pins on the cockpit bail mount. A quick clean of the connectors and all is good. Quite why Garmin didn't use stainless for these pins is beyond me but easily managed.
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Old 20 November 2018, 07:55   #6
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I am in the middle of a rebuild so have all options open to me.

For two reasons I prefer mounting it in-board, 1. Its far less vulnerable 2. No external holes thru the gel coat and GRP to let water in to the wooden transom.

My question was really just what to use, epoxy or silicon? As the downside of the in-board installation is it will be sealed up before i get a chance to test it.

Many thanks
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Old 20 November 2018, 08:18   #7
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Personally I think it asking for trouble to permanently fit electronics in an inaccessible location, and compounding the matter by not testing prior to committing.

A transom mounted transducer is not as vulnerable as you think. It sits on a hinged mount, so worst case it gets knocked up or down, and you simply push it back into place.

Drilling a hole through the transom above the waterline is nothing. Just seal it up. After all, you will have 4 holes through the transom to take the motor !

You are overthinking this and potentially making a big problem for yourself.
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Old 20 November 2018, 12:49   #8
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I take your point, but I don't want the clutter on the transom and the cable drapped over it.

I am going to have a sealable inspection hatch thru the base of rear seat to gain access to the transducer should there be a problem.

So question is, do I fix the transducer down with epoxy (permanent) silicon (semi-permanent)?

I have a preference to use silicon, but I asked to make sure this wasn't madness

Outboard bolts are bigger and easier to get a proper seal.

Many thanks
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Old 20 November 2018, 17:39   #9
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The transducer we have garmin p79 sits in a socket. This socket is sikaflexed to the hull. The transducer is then inserted into the socket which has a bath of antifreeze in it. The transducer can be easily removed. I like the above idea of the sealed drain pipe. As said ,some day the transducer will need looking at ,so id try and keep it serviceable. Nik
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Old 20 November 2018, 19:57   #10
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External no problem, no holes needed if you use the transducer pads. Standard $180 transducer.

Depth in metres, as mentioned external mount allows me to tweak the transducer even while offshore over deep water. 50khz shows bottom quite nicely at 600m if I pull my speed right back but as can be seen in the screen shot, I have no probs holding bottom at 250m+ over 20knots.

By the way when you mention deep water, how deep are you wanting to sound ?
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