In-Hull Transducers

[wynnstow]

Anyone had any experience of using in-hull transducers compared to the traditional thru hull type? I have 39ft GRP motorboat with Raymarine ST40 instrument and in-hull transducer. Depth reading even at moderate speeds disappears in calm conditions. Their seems to be a train of thought that in-hull transducers are more suited for smaller and slower boats with thinner hulls than my type of twin engined boat.

 

[Medskipper]

I have a in hull transducer for my depth guage and it works fine on my 37 foot motor cruiser. It is important that the sender is covered with oil, I use olive oil! its also important to get the sender pointing correctly straight down and not to near the stern, so around midships should do the trick. Its best to clean all paint off the surface of the hull before mounting the sender on it.

Barry

 

[finnlou]

sounds like your transducer may be mounted too far forwards

 

[Dave_Snelson]

I have a Navman in-hull transducer on my Windy (Windies don't have thin hulls) and it was fine when I first fitted it, but it deteriorated after time. I found that the mastic that I had used had perished, and was advised to use Dow-Corning clear marine silicon, which I did. But first I cleaned the area of hull inside with soap, water and then acetone - flippin' spotless is what you need. Position is also important, about 1 meter forward of the transom should do, and just above the bottom of the Vee - not in the tunnels between the strakes.

Squeeze out the silicon and press the unit into it with the slope of the unit acting to counter-act the slope of the Vee of your hull. Ensure you have no air bubbles in the silicon as you dispense it, then press the unit into it, squodging the stuff out as you go. Fix the unit in place with strong duck tape and leave to set for two days before removing the tape.

Initially, before fixing the unit, you could try an easy experiment by filling a plastic sandwich bag with water and putting the unit in in and holding it against the inside of the hull. The bag and water form a perfect shaped seal, just as the mastic does, and you can enlist some help to watch the read-out.

 

[duncan]

got three basic skimmer 'ducers stuck into the inside of my hull in various places and they are as good there as on the transom although the forward one (pretty much under the helm seat) suffers at 25 knots in a chop.......... /forums/images/graemlins/crazy.gif but I still get a depth indication.

Dave's suggestion of a sandwich bag full of water is excellent - another alternative is one of those medical cool bag things full of gel (but not necessarily cold!) if you have one lying about. Try different areas until you get a good signal.

I have one stuck in with silicone, one sikaflex and the other plumbersmate epoxy - no difference 'cept the silicone and sikaflex are easier to cut out again!

All this presumes you have an available area of single sheet composite material in your hull somewhere! Any sandwich/foam core/stringers etc make it a no no area.

 

[omega2]

Dave and Duncan are singing off the same hymn sheet as me, I have a thru hull transducer shooting thru the hull, too idle to cut a hole!!

 

[richson]

I have used in-hull types on a Seaward 23 (Nelson) and a Jeanneau Leader with no problems. Silicone is easier to use, but has a higher vswr than epoxy (which most manufacturers recommend) and so in theory will reduce the signal strength. I doubt that anyone would notice the difference though. Maybe find a good spot with silicone or with Dave's water bag, then epoxy it in. Both methods it is v important to ensure there are no air bubbles in the glue.
The transducer should be mounted where the hull will be in water, but not in any turbulence or aeration. Immediately behind an existing through hull transducer for example, would be a bad place.

 

[coca2005]

sikka flex 252 is perfect for in hull transducers (just a quick passing coment)