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Thru Hull vs In Hull Transducers

Discussion in 'Electronics' started by Aaron McCann, Nov 28, 2021.

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  1. Aaron McCann

    Aaron McCann New Member

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    There are a few in-hull transducers that have pretty great reviews. They seem to have obvious advantages if they work comparably to the thru hull designs. Thoughts? I am researching a Garmin refit for a 1981 42' Ocean SS. I have zero experience at this and appreciate any help or suggestions.
  2. motoryachtlover

    motoryachtlover Senior Member

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    I am far from an electronics expert but I have had crappy luck with depthfinder transducers mounted on the inside of the hull. I assume that is what you are asking about. I am not an avid fisherman so I was only using modern depthfinder tech. Don’t know if there are some other hull mount transducers that do well with cutting edge fish finders.
  3. Capt Ralph

    Capt Ralph Senior Member

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    Can you hear me?
    Can you hear me?


    Oh wait..
    Let me talk to you outside of the hull.

    Can you hear me now??

    If you are into fishing or really need to read the bottom for anchoring, Then you will want a thru hull mounted transducer.
    If you are pushing just a digital depth sounder, An in hull puck may work.


    Some folk get lucky with their inside mounted ducer, some folks crash & burn and swear never to be so cheap again.

    IMO, do it rite the first try, Get the best thru hull ducer your checkbook can afford.
    Aaron McCann likes this.
  4. Aaron McCann

    Aaron McCann New Member

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    The in-hull units I looked at range from 1000-4k. On the higher end the Airmar R599 @ 4500.oo hardly seems cheap? I can't find anything thru-hull that runs that expensive, but more expensive don't mean better for sure. I was just thinking no more holes in the hull does equal more better.
  5. Capt Ralph

    Capt Ralph Senior Member

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    Reuse an existing hole then.
    Better yet? What ducers do you have installed already?
    Most ducers are mfg'd by Airmar corp. You may already have a good ducer installed.
    Look for a tag close to the ducer and cross it back to the Airmar standard.
    Aaron McCann likes this.
  6. Aaron McCann

    Aaron McCann New Member

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    Thanks Capt. Ralph, I just assumed the transducers were of the same vintage as the boat and would be out of date and not compatible with new gear. The only electronics working is an old analog radar unit. The last owner ran a hand held and a prayer, but the boat never left the Puget Sound.
  7. Capt Ralph

    Capt Ralph Senior Member

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    Again, depends on what new gear.
    Just a pinger, 200htz has been a standard since Moses.
    You may already have one installed.

    The latest gizmos, Chirp, Side view and more are later designs. Usually made by Airmar also for the different mfg's.
    If not compatible, there is an existing hole in your hull.

    Don't kick analog radars to bad. I'm still using a 15+ year old 10KW x 6' pedestal unit.
    AND, spares in the shop.
    Aaron McCann likes this.
  8. mapism

    mapism Senior Member

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    I understand a hand held plotter - some charting softwares for tablets are actually pretty good.
    But as a depthfinder replacement...??
  9. Aaron McCann

    Aaron McCann New Member

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    He had some transom mount screwed to the swim platform.??????? It probably worked at idle but much passed that no way. This boat needs 20k of sweat equity easy! I saw the head unit in a soft bag, told him to keep it. It's such a safety issue I don't get just winging it?!?!?!? I just want it right.
  10. CaboFly

    CaboFly Member

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    The In Hull ducer is for boats that have a high cruise speed and want the power of 2kw or 3kw transducer to shoot deep. I had a R599LM on my 40 Cabo and it worked great. I wouldn't want a 3kw fairing block on a 40ft hull that cruises at 30 knots. Another consideration is mounting location options. You also need a hull that has very high quality glass layup with no air bubbles.
    On a Ocean Yacht I would mount a 1kw powered thru hull on a fairing block. Years ago I had a 40 Ocean SS with a Airmar B260. Worked fantastic.
    All things being considered on a boat with space near center line for transducer with accessibility I would go thru hull over in hull. I would also use a fairing block. On larger boats the low profile transducers dont work well beyond hull speed.
    Aaron McCann likes this.
  11. Aaron McCann

    Aaron McCann New Member

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    I'm confused, first you said you wouldn't want a fairing block, then you said you would use a fairing block. I know this boat isn't fast by today's standards but 20-22 isn't trawler slow.
  12. mapism

    mapism Senior Member

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    What I would do (and in fact I did, in my own boat) is fit one of the Airmar thru-hull flush transducer, which don't require any fairing blocks.
    As I recall, there is a 600W and a 1kW version, and both are available with the internal element already tilted - either by 12 or 20 degrees.
    So, depending on the hull deadrise in the installation area, you can get an optimal vertical coverage even if externally the transducer remains flush with the hull surface.
    bayoubud likes this.
  13. CaboFly

    CaboFly Member

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    A 1kw size fairing block on a 22knots boat is no problem.

    A 3kw fairing block is much large and if not mounted on centerline can have consequences at 35 knots.

    Go to Airmar and poke around a bit. Look at specs. Do some searches. What expectations a person has that just wants to mark bottom vs a fisherman who wants to see separated arches at 800ft are very different as well.

    Just posting my experience after installing about 8 transducers the past decade.
    Aaron McCann likes this.
  14. DOCKMASTER

    DOCKMASTER Senior Member

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    I put one of those thru-hull ducers in my 14' RIB I carry on the bow and it has been a PITA. It has to sit with liquid between it and the hull and when it leaks out of the enclosure to hold it the dang thing won't work. Fixed it again last season and we'll see how long it works. I don't know if they all work the same way or if just the model I ended up with.
    Aaron McCann likes this.
  15. cleanslate

    cleanslate Senior Member

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    I have a Airmar P79-BL for my Simrad unit. They make them for most mfgs. out there. It's the screw in end / cable that must fit into your unit. That varies. It costs around $200. Mine has been great for three years now. Very accurate and no jumping around. Remember , our hulls are thin! Easy for it to shoot through.
    Just follow the installation instruction to the letter. It will work great.

    I removed two of the original thru-hull transducers that went to old out dated electronics.
    I plugged the holes.
    AND my boat is not a fishing boat. All I want is the depth keep in mind.
    Last edited: Nov 29, 2021
  16. cleanslate

    cleanslate Senior Member

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    Yes you have to fill them with liquid. I used pink antifreeze so it wont freeze and break in the winter. You shouldn't use plain water. Works fine in my big boat. Not a lot of slamming around like a speed boat.
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  17. mapism

    mapism Senior Member

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    That's what also my boat came with, connected to a Raymarine sounder, and in fairness it worked acceptably well.
    But as Dockmaster said, sooner or later the enclosure leaks out the oily liquid in between the transducer and the hull, and re-sealing it can be a PITA, after the enclosure and the hull bottom have been oiled for years.
    By the time this happened to my unit, I had already decided to replace it with the flush thru-hull unit I previously mentioned (called B60, as I recall), so I thought I had nothing to lose by trying a very simple fix (against the advice of a specialist), in the hope that it could last longer.
    Instead of trying to re-seal and re-fill the enclosure, I just cleaned the inner part as well as I could, filled it with some silicone sealant, and pushed the transducer back on it, till some silicone squeezed out.
    And believe it or not, it did work, with no noticeable performance loss - and no risk of leaks, of course.
    Now, I'm actually using the other thru hull unit that I fitted in the meantime, and it does perform a bit better.
    But if and when it should fail, all it would take me to restore the old unit is just re-attach its connector to the sounder, after disconnecting the new one.
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  18. cleanslate

    cleanslate Senior Member

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    I do not use oil.
    Just “pink” winterizing antifreeze.
    No big mess.
    Mine is easy to get to so that helps .
    Clean area good with acetone, seal down outer tube with fast cure 5200. Let dry.
    Fill about half way with antifreeze and set the round transducer in. Let the excess antifreeze spill out as you push it down . install the screws to hold down and seal the transducer to the outer base, and you’re done.
    Three years , good so far.
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  19. mapism

    mapism Senior Member

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    Fair enough, but that still relies on the outer tube to remain 100% liquid tight over time.
    Mine started leaking when the boat was already 13 years old, so I guess I can't complain.
    But I'd expect my silicone alternative to even outlast the boat now, also because it's fully enclosed and protected.
    Time will tell...:)
  20. Capt J

    Capt J Senior Member

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    take the liquid out, and epoxy it in with clear epoxy, set it directly in the epoxy, it will shoot right through no problem
    MBevins likes this.