I am hoping to improve the reliability of my depth transducer system at the next haul out. My current system is a cheap bullet transducer in a wet well mounted in the bilge on the inside of the hull. The wet well is made from a plastic sandwich box with the bottom cut off, and I periodically fill it with water and/or radiator coolant. It works most of the time, but not enough of the time to be reassuring.

Previously, I had thought of two options
1 Through-hull transducer mounted in a hole-in-the-hull. The transducer before my current bullet is like this, which means I have a 30mm hole already in the hull. I've kept the transducer in place for obvious reasons (if I remove the old transducer, I have a 30mm hole in the hull below the water line. I have a plug, but don't want to risk the changeover until the boat is out of the water)
2 In-hull or external bullet. Most cheap fish-finders are designed to be mounted externally on the transom of a tinny. They can be mounted inside the hull using a wet well, like my sandwich box, which can be improved by filling with resin or goo. This approach will not work for sandwich-hull construction or timber, but seems to be OK for solid GRP hulls, like mine. I had previously bedded the bullet in with strong goo, but slightly damaged the housing when I tried to check it and relocate it. Next time I will use a soft or weak goo.

There is also a third option, demonstrated in the re-fit of Lyra by Tim Lackey lackeysailing.com/lyra-60/. This uses a cut-out and moulding in front of the keel for the transducer. I emailed Tim, who replied that the transducer was provided by the boat's owner, and is a side-scanning sonar like a Garmin GT30-TH. buy.garmin.com/en-AU/AU/p/537083 (the photos show that it is not the exact model). Tim advises that "Any regular transducer (i.e. not side-scanning) will shoot through a solid fibreglass hull from the inside, if installed properly (usually in an air-free mass of silicone or epoxy against the hull). Or invest in a good, metal (bronze) through-hull transducer (which I admit is still my preference)." I didn't ask if Lyra's transducer will be painted with anti-fouling.

So, I'm thinking of the following plan
* Get a new good-quality through-hull to replace the old through-hull in front of the keel (My chart plotter is on the blink as well, so I might go for an integrated system, if funds allow)
* Relocate the cheap bullet elsewhere in the bilge and fill the well or bed it in with soft goo. This is a backup, and makes use of something I already have.

Finally, the mass-market is oriented to fish-finding, which is not what I am looking for. I want to reliably know the depth in less than 5m of water to prevent grounding and to estimate the length of anchor-chain needed. I am not interested at finding fish at a depth of 200m. The solution seems to be the higher frequency transducers, which have a shorter range but greater accuracy than lower frequency transducers.

The transom mounted fish finder transducer are ok with an outboard as they are forward of the prop but are affected by prop wash from an inboard, I carry one as a backup, it's also handy to throw in the dingy to sound possible hidie holes or for fishing, the colour of the bottom is an indicator of the type of sea bed

I had a very out dated depth sounder and a very outdated plotter and updated to a ( now old but not outdated sidescan fish finder plotter) integrated Humminbird which is accurate to three feet in position and allows me to side scan for isolated bommys or coral out crops in a potential anchorage by doing a small loop in proposed anchorage, and I don't think I will ever regret it or go back.

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stupid said..
I had a very out dated depth sounder and a very outdated plotter and updated to a ( now old but not outdated sidescan fish finder plotter) integrated Humminbird which is accurate to three feet in position and allows me to side scan for isolated bommys or coral out crops in a potential anchorage by doing a small loop in proposed anchorage, and I don't think I will ever regret it or go back.

Hi ,
How have you installed your transducer?
How is your boat powered ie outboard or inboard?
Thanks

Sorry to say the cut a hole in the hull option imho should never be done.

In a past yacht (Compass 750) I had an old basic Piranha 1x depth sounder and wanted an in-hull mounted inside of the hull laminate scanning through the hull skin no holes needed (single skin grp as you say - no good for sandwich grp or timber) transducer for it - I emailed bla and they immediately came back with;

As long as your Piranha is a multi-pin Transducer it will fit. Part no you will need is - 103307 - Transducer Puck 200/83khz SGL/Dual Beam - Retail $ 189.00 Yes it is available You can purchase via any Marine Dealer nearest to with a BLA account You can find these via our Store locator on either - www.bla.com.au or www.humminbird.com.au

I bought this and installed it as per the instructions and it worked perfectly - depths were only in feet though. Maybe your readout has the metres reading but even so to avoid a hole in the hull I would be happy with feet again and am looking to repeat the above with a used readout and new transducer in current single grp skin yacht, no holes. On the slipping of this yacht in August I will fill in and cover over the old through hull transducer hole and speedo transducer hole - for both epoxy 9mm ply doubler pad probably 100-150mm diameter inside, tapered periphery and epoxy resin and glass over it, high strength epoxy filler to fill it, epoxy glass faired in on edges outside to finish off.

I bought a hawk eye in hull depth sounder a few years back and and stuck it to the hull with sikaflex after sanding area smooth. I have no complaints with it.
What you may be interested in is that when they sent it to me from the US they sent an airmar through hull P19 transducer in error. They sent me the in hull
and asked I return the through hull ,at my expense . What!
Its still in box. If it is compatible with your display its yours foc.

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Bananabender said..
Its still in box. If it is compatible with your display its yours foc.

I'm interested, PM sent.

In hull utilising a plastic box full of water works perfectly.
BUT, one needs to test the area carefully as solid fibreglass hulls are not consistently solid ie could be some very small air spaces.
Put the transducer in a plastic bag full of water and secure in different locations to establish the most effective spot.

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warwickl said..

stupid said..
I had a very out dated depth sounder and a very outdated plotter and updated to a ( now old but not outdated sidescan fish finder plotter) integrated Humminbird which is accurate to three feet in position and allows me to side scan for isolated bommys or coral out crops in a potential anchorage by doing a small loop in proposed anchorage, and I don't think I will ever regret it or go back.

Hi ,
How have you installed your transducer?
How is your boat powered ie outboard or inboard?
Thanks

Not that I think it's relevant anymore , it's through hull, inboard motor.

I have mounted my Lowrance Triple Shot bullet transducer inside the hull bedded in silicone (no air bubbles) in my Cav 28 Port side under the sette just above the stringer. Its protected there and works perfectly other than the water temp which I can live without. I trialled it first in some water sitting in the same place. The stringer formed a perfect dam for the trial.

Revisiting this thread because I still do not have a working solution.

My attempts at mounting an external puck in an internal wet well have not succeeded. I am not getting reliable depth readings at shallow depths.

I also have a donated Airmar B19 through-hull, which I have not fitted yet. I emailed Airmar a photo of the plug (see below), asking what I might need to plug it into a Garmin head, and Airmar responded with "That picture is not a connector that we are familiar with and has not been used on B 19 transducers."

Laying out the cards on the table ...

* Looking for something that gives a reliable reading of depth at shallow depths, at low speeds and on muddy bottoms. Not interested in finding fish at 200m. Not interested in something that "performs well at high speeds" (a phrase often-repeated in the on-line blurbs, obviously appealing to the fishing market).

* Most reliable option appears to be a through-hull in a metal housing.

* Airmar transducers are used by most (all?) of the instrument-makers (Garmin, Lowrance, B&G, etc). You just need the right connector, or an adaptor, to plug one into the other (Airmar's confusing email to me notwithstanding)

* I don't want to spend less than I have to, but also don't want to spend much more than I have to, for features that I don't need (e.g. I don't need a speed wheel). Do I need CHIRP?

However, looking at the range of options on-line gives me a price range from about $220 (Airmar B169) to $810 (Airmar B75H), which is too broad to work with. Please help narrow this down.

That plug was probably attached by Hawkeye who sold those transducers with their Hawkeye depth displays.
Find out from Garmin what connection you need ,chop off the Hawkeye one and solder on new one connection wires correctly.

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Bananabender said..
That plug was probably attached by Hawkeye who sold those transducers with their Hawkeye depth displays.
Find out from Garmin what connection you need ,chop off the Hawkeye one and solder on new one connection wires correctly.

Thanks, that would explain why Airmar did not recognize the plug.

Finding the on-line sales blurb difficult to interpret for my particular needs, I emailed Airmar with the following broad specs ...

* Through hull
* Bronze housing
* Reliably provides depths at an accuracy of, say 0.1m, at a depth of 5m or less - this is the most important feature
* Good at low speeds, up to about 7.5 knots (my boat will not go any faster)
* Good for angles of heel up to about, say, 30 degrees
* Good on muddy bottom
* NOT interested in finding fish
* NOT interested in finding depths over, say, 60m
* NOT interested in working at high speed, say over 10 knots
* Probably NOT interested in speed wheel, but might consider it if the depth reading is very reliable
* Head/display to be decided, but might be Raymarine i40

Airmar emailed back with the following

The Airmar DST810 is a good choice if you use a NMEA 2000 display but it will not work at 30 degrees of heel. The sensor has a maximum angle of 22 degrees to include the deadrise.

Shallow water performance is very good but again, there are no specifics given due to how variable the bottom is as well as the installation although generally anything above a meter is good.

The Airmar web-page shows a plastic housing, but it appears you can swap it out for a bronze or stainless steel housing.
www.airmar.com/productdescription.html?id=222

There are some threads on Airmar DST800/810 issues, especially the reliability of the depth reading ...
www.trawlerforum.com/forums/s4/airmar-dst800-problems-again-35459.html
forums.sailinganarchy.com/index.php?/topic/157226-raymarine-airmar-dst800-transducer-issues/
panbo.com/marineelectronicsforum/panbo-forum-general-discussion/dst810-false-depth-readings/

... but there seems to be no real alternative to Airmar

Any comments on the DST810?

Achernar, just wondering how your sender dilemma went ? I was watching closely as I had to get a simple and reliable sounder for my work boat, in the end I went with raymarine i40 display and b17 transducer.

Don't worry at all about cutting a hole in your boat. Install the transducer you need and if you need to drill a hole then no worries.

I epoxied my plastic transducer in place about 21 years ago. It is part of the hull structure. If your boat is glass it is a holesaw and then careful smearing of the transducer with epoxy on the bottom as it is installed. If you have composite there is more work, but not much.

To remove the tranducer will be a pain but that is okay, I am used to painful things and the lack of concern after epoxying a fitting in place is worth it, no leaks, no worries.

Put a ply doubler (covered with clear epoxy) glued to the inside and cut the hole. It is not a through hull, there is no movement and it is not a log which can be pushed back in, it is very strong and able to take wave slams fine.

Just one thing, check the unit. When I installed mine all those years ago, I launched the boat and the depth sounder didn't work. I called the company and they said "You stuffed the transducer wire in the install" I said I didn't as I was really careful but they said no head units ever fail. I knew a bloke who had the same unit, took his head unit off his boat and lo and behold it worked in my boat. Glad I didn't listen to the experts then.

Epoxy is your friend, it loves most PVC type plastic.

@woko I might have a solution. I used the weakest filler I could find , Parfix, to glue the bullet inside the hull. It appears to provide readings that are reliable enough to avoid the shoals. Trying to keep silicone away from the boat.

Achernar glad to heard you found a solution that works for you in hulls work good in glass boats and don't be afraid to use epoxy you can make it let go, I think the term is destruction.
Kankama I appreciate just how good epoxy is and the B17 will be epoxyed in with a well epoxyed and glass taped fairing block, same set up as on my steel hull, just bronze & wood while the other is steel & plastic

So starting to line up all the bits & pieces I need for jobs I want to do on my new old wood hull, looking over the installation information for the depth transducer ( airmar they all are ) says to use waterbased anti foul, I've been rolling the like of jotun sea Guardian over a very similar unit on my other boat for 8 years. What does everyone else do ?

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woko said..
So starting to line up all the bits & pieces I need for jobs I want to do on my new old wood hull, looking over the installation information for the depth transducer ( airmar they all are ) says to use waterbased anti foul, I've been rolling the like of jotun sea Guardian over a very similar unit on my other boat for 8 years. What does everyone else do ?

The same but on my fishing vessel the face of the transducer was like a rubber compound and I would leave that bare.