New take on transducer attachment.

I used Promethean's pool noodle transducer mount idea on the Hobie Adventure and it really works well.  Thanks, Josh!

I am an official big fan of this install.

I did it in my new prowler, and I can say that I cannot percieve a difference in performance with this install and the transducer directly in the water like I had on my drifter.  The only issue is that the temp is not accurate, but the sonar works perfectly.

Kudos to the Spark for posting this idea up!

MolBasser

I had problems with my goop installed transducer so I switched to this setup. I had it out today for the first time and it works great.   

I couldn't come up with a pool noodle large enough to work for me. So instead I cut the bottom 3 inches off a lemon pepper spice bottle (large Costco size). Then I cut the bottom out of it so the transducer would only have to read through the kayak hull still. Marine siliconed the piece down and made sure of no leaks. Works perfect, I rigged it up for a sudden trip but it worked so well I'm going to leave it.

Thanks for the idea.

I am curious to know what kind of problems people seem to have with gooping their transducers in?  Is it lack of adhesion or artifacts from errant reflected sound or poor penetration to intended depth? I have a Lowrance C68 and have never seemed to have had problems with it just "Gooped" in.

As with light waves, sound waves are most likely reflected back at the interface of two dissimilar materials.  The greater the difference in density between the two material the greater the probabilty that energy will be reflected back.  Since the transducer cover, cured Goop and the kayak hule are all verious forms of petrochemicals-haydrocarbons- I would bet that their relative densities are quite similar, therefore lowering the risk of reflected energy and lowered penetration.  But with the foam "cup" mounting, you go from epoxy to water (and any potential air bubles) back to polyethylene and then back to water.  I would think this would create a greater chance for artifacts and attenuated wave energy.

Also, wiith this foam retention system, I would think that if your kayak hit enough turbulence you could dislodge it a bit or lose a bit of water and potentially introduce an air buble between the base and kayak, thereby introducing "built in" artifacts.  Or if you flipped your kayak and lost waterI would think you would have to enter your foward compartment to fill up the foam "cup" with water if any of it leaked.  I guess if the seal around the transducer is really uniform and tight it would retain the water even if the kayak was upside down. 

Probably not of practical significance since the application demands are fairly crude--its not like were searching for enemy subs.  But I was just wondering.

Doug

With my transducer gooped in I would occasionally get some very innaccurate readings  -- when I was in 40 -50 ft of water it would randomly start incrementing upward to 5-600 feet, then work fine for a while,  and then error out again.  When I finally tore it out it it seems there was only partial adhesion on a section of the bond and water was seeping in and out of the joint as the hull flexed, causing problems (I suspect it was working well only when water was in there).

I used a good sized (fairly deep) block of "pool noodle foam" that was used to pack some mail order furniture for my mount - I used a contour gauge on both ends and carved it to fit the bottom profile of the hull.  And then I carved the transducer hole very undersized, so it's a real tight fit.  When I insert the transducer I fill the cup fairly high and then squeeze a lot of the water out to ensure no air bubbles.  It holds the water even upside down on my truck on the way home after fishing. Also I positioned the mount block where I *can* reach it from the front hatch, primarily so I can easily stow my rods around it when I put them inside for landing.  So far the transducer hasn't moved a bit, in conditions as rough as I care to test. I suppose if you had something moving around a lot inside your hull it could pull the cable, but that's a good reason to make everything neat and tidy with cable ties and lash downs when you do the install.

Chris.

I've also never experienced any difficulty with my goop-mounted transducer.  I did have to replace the power cable on my Humminbird Piranha Max15 once, the connector at the head end corroded probably due to my ignorance.  Since, I have given the connectors a fresh water rinse down after disconnecting and a shot of Electronic Cleaner from West Marine (thanks Randy) when I get home.  I did have a total unit failure and opened the case to find it pristine inside.  Something to do with the processor shutting down from intermittent power.  Sent it to Humminbird after the warranty expired and they still fixed it without charge.

I might give the snug noodle method a try next time though.

I have gooped mine but I can see the utility of having a detachable mounting regime. However, in rough water or surf launches, might the water not leak out? It might be better to put the foam holder in a glued-down pvc tube with a cap on top: fill and cap off each trip and the water stays in.

As for foam under the transducer--no! The sonar waves change speeds in different media and can reflect as well. And air voids are a big problem because of their signficant difference in density even though the distance is short. This includes air bubbles in goop-ed installations and can be one of the most common problems with them. That is why I had to re-do the one in my Prowler 15 the first time I installed it unfortunately. In fact, sonar speed is different in fresh and salt water also so measurements are off in one or the other depending upon which you tune your receiver for--but not by much. Some sonars (maybe all?) have a menu option to select fresh or salt water. As for the difference in between plastic and water--my guess is that for a small distance relative to the whole distance being measured it is not material given the entire signal path length. I am no expert, but my guess is that fresh versus salt water speeds of propagation are only significant at depths where the length of the medium is signficantly long to delay the signal enough to create a depth error.

Reflection back from the interface is not related to the distances involved but to differences in material densities.  As you mentioned, salt water is more dense than fresh water and hence the differential speed in sound wave propagation.  But the differential in transit speed does correlate with the potential for reflecting waves backward. The greater the difference in density, i.e. plastic/"plastic"/plastic, v.s. plastic/water/plastic, the greater potential for reflection.

That's why submarines can get aberrant signals from thermalclines--layers of water at different temperature--because even the change in water temperature changes the density of the water enough to reflect sound waves back to their accoustic sensors.  It's like light being reflected off a pane of glass.  The light doesn't have to transit through the glass to be reflected back from the proximal air/glass interface; and light that gets through the glass can reflect back off the distal glass/air interface without ever transiting beyond the back side of the glass.  So even a thin layer of water can cause a reflected wave.  But of course this is probably not practically relevant for our purposes since this is a rather crude application of physiics.

I've seen thermoclines with my sonar before......

I think that any interference between the water/plastic/water (as long as there is no air) is just lost in the surface clutter signal. 

I can only report what I see in the field, and that is that this mount works great.  I have no problem whatsoever seeing a 1/16oz crappie jig at 20 ft + with this install (I'm sure I could see it deeper, just haven't ever been in a situation to see it deeper yet).

MolBasser

When I get some time on my hands, I'll remount my transducer using a 2" PVC pipe with foam inside and use a cap and report.
I need to find a contour gauge (Home Depot or Orchard Supply?) as it will come in handy shaping the pipe bottom to the contours of the hull.
But as of right now that crochety old Irish man, Murphy, is whispering in my ear "if it ain't broke, don't fix it" and "go fishing instead"  . Actually he's really saying"have a snort of good Irish Whiskey instead" but I knew what he meant  . I just know he used to kayak--I feel his presence out there on the water sometimes.

I have read in a sonar manual or two that the manufacturers actually recommend testing the position for a 'shooot-through-hull' installation in a boat using a cup full of mineral oil not water. I assume that is because the mineral oil's density more closely approximates than of fibreglas or in our case, polyethylene. The difference is probably not material and water is far more practical. If I cap the pipe I could use mineral oil but I don't like the idea of the inevitable leak coating my gear with mineral oil so I won't try it.

It's easy to make a contour gauge (or reasonable facsimile) with a narrow block of wood, duct tape,a sharpie and two pieces of cardboard:

1. Position foam block where needed and mark location on hull.
2. Tape sharpie to top of wood block and remove cap.
3. Position wood block at front of the area you want to profile, withthe point of the sharpie pointing at the bow, and hold the piece of cardboard in front of that.
4. Keeping the wood block vertical, move it across the hull contour so the profile is drawn onto the cardboard.
5. turn block around and repeat for the sternmost line on the other piece of cardboard.
6.Then just cut the cardboard along the sharpie lines and you have the hull contour at the front and back of the foam block.

I traced the lines on either end of the foam and carved with a ham slicer from the kitchen (I'm the chef of the house so no WAF points diminished).

Chris.

CPDW, thanks for the contour tip it'll work in a pinch and its so cooly 'ghetto' because it involves duct tape. I like it . But now I have to buy a Ham Slicer  . Just kidding I'll use my Dremel for more 'ghetto' points and earn WAF points as well for not comandeering kitchen utentsils or equipment for kayak projects 

I wouldn't reccomend trying this with PVC.  The most useful parts of this for me are that I can remove all the electronics from the hull between trips and store them in a better place, and that a bump to the hull will not tend to dislodge the foam because it is soft and bends with the hull instead of popping free.   The hard PVC will get you back to the problem where it can pop off.  I'd rather have to re-seat the transducer or add more water than need to re-goop the holder.  In 4 years of fishing I've never flipped outside the surf zone, but 4 times I've gotten to the beach in the morning and opened the hatch to find the gooped tranducer had come undone.  The amount of water needed is pretty small, about 1tbsp (what I can carry in 1 cupped hand) and the transducer holds it in like a cork since it fits tightly into the foam.  The transducer isn't heavy enough to fall out if the boat flips over.


Since the foam is flexible, I didn't make a production of cutting a contour in it.  I just applied silicone and put a 5lb dive weight on top of it to hold it down.

Got it. Leaving over-engineering in the dust. I just used marine silicone to cement down a rectangular piece of closed-cell foam (Bill gave me when I visited him over the weekend--thanks Bill!) jsut liek I saw Sean had set Bill's up. Its between the scupper holes along the gunwales on the Marauder. I traced out the outline of the tranducer on it and cut it out about 1/8-inch to the inside of the outline to make it very snug. I'll try it out in a sedate place like Delmonte Beach Monterey and see how it works. The install is so easy, re-work in the event of problems will be simple and fast (an overnight set and dry). I don't plan on removing my transducer though except to pull it out between voyages: the cable-through-hull setup requried with the Humminbird 76 with GPS, trandsucer, temperature, and battery requires a non-temporary cable-to-mount setup. But I mounted the transducer with foam anyway because it is much more easy to fine-tune the alignment than gooping it in and I won't get to the launch one day to find teh gooped transducer loose ruing a trip either.