Bc23 position of echo sounder transducer

[Quasinix]

Hi Forum,
Can you tell me where the best location for the signal transmitter from a depth sounder on a BC23 is?
I have put it in the locker under the galley sink inside the hull. No hole. But I get no good signal.
Do you have an Idea?
Kind regards

Jan BC23, No. 71

[Graham W]

In the absence of any answers to your query, I found this in a BC23 post by Andy Dingle in 2017:
"Note the BC23 has a 'cored' hull so the 'shoot through' transducers don't work. You'll need a hole drilled through your hull for the transducer! As standard I think this is under the sink, so Matt will need the transducer as he builds the boat.
Having said that, I've just fitted a 'secondary' Garmin striker depth, using the supplied transom transducer that I fitted on a bracket under the boat from the outboard mount, in the outboard well - works great!"

[Quasinix]

Hi Graham,
Thank you very much for your answer.
I have not found any post about BC23 and transducer. I think my english is to bad😉
Now I surely know that i have to drill a hole.
Kind regards
Jan

[Sea Simon]

OP. It depends...
What make/model of D sounder and transponder head are you trying  to install?

GW and AD are correct you can't use internally mounted "shoot thru" transponders inside a foam cored hull...generally. Plenty of sounder manufacturers  explain this.

I managed to find a spot for my "cheap" shoot thru NASA Clipper unit in the cabin of my BRe (foam cored?), but it was far from perfect.
On those boats, I later learnt from this forum that it's far better to mount the transponder up inside the board trunk. I can't see a way of installing  the transponder like this on my BC26. It MAY be possible on the BC23?

I tried to find a way to get a new, cheaper, NASA Clipper to work on my BC26 (also foam cored hull) when my v expensive Raymarine combi chart plotter/sonar unit failed, week 1 of my ownership!
Using the live NASA shoot thru transducer head as a form of wandering extension lead, I tried temporary installs all over the BC26.
I had little success, and while the NASA depth does sort-of work, it is unreliable, through no fault of the unit.

As I use a portable tablet for nav, and as the boat has now had two £1500+ Raymarine plotter heads in < 10 years, I had to try!  I'm NOT buying yet another plotter display, chart updates etc etc...! Besides which the plotter sounder numerals are too small to see from the helm.
In a moment of winter sale madness, I almost succumbed to the temptation to fit a new set of BnG instruments,  but fortunately  I rememberd this distance problem. I have no console/binnacle etc to mount instruments,  they have to go on the cabin bulkhead. Some 6-7ft from where helm sits.

So I used the existing thru hull (seacock type) with AIRMAR brand (common standard transponder brand, used by Raymarine and others) combined speed/temperature, and depth heads to drive a new, separate, fairly large (almost as large as the Clipper display), Raymarine digital/numeric display. This works well, but the D transponder seems very prone to fouling. Airmar say not to antifoul it, with solvent based paints.
Unlike the speed paddle wheel it is not "withdrawable" for cleaning. It was SOLID with barnacles after 4 months afloat.

Airmar brand transponders cost 3-4 times a s much as NASA. But still cheaper to buy the same thing from Airmar dealers than via Raymarine.

This winter I hope to sort the NASA Clipper install, to give a backup/reserve/second opinion depth sounder!
Much needed to calm my frayed nerves when navigating the upper reaches of the Tamar, to Calstock and beyond. There seems to be much more rock than the Fowey river where I'm based.

I plan to follow the Airmar install instructions: Very carefully cut away the inner skin, excavate the foam core to expose the still intact outer skin. Backfill the resulting recess with epoxy, then install the shoot thru sounder, bonded internally above this new solid epoxy hull patch.
Hopefully, this method means that the antifoul on the outer skin can stay intact? No holes right thru the hull.

I don't want to use the available NASA kit to install the Clipper transponder thru hull, as it seems a bit vulnerable  for a boat that intends to beach/ground fairly regularly. Doubtless it too would also foul up quickly?

[Sea Simon]

UPDATE.
"I plan to follow the Airmar install instructions: Very carefully cut away the inner skin, excavate the foam core to expose the still intact outer skin. Backfill the resulting recess with epoxy, then install the shoot thru sounder, bonded internally above this new solid epoxy hull patch.
Hopefully, this method means that the antifoul on the outer skin can stay intact? No holes right thru the hull."

Fitting to foam cored hull.
Launched weds.
This works. I now (somewhat unintentionally) have three fully functional depth readers, one a fish finder! One external, two internal shoot-thru hull.

Raymarine fishfinder sonar as far forward on stbd side as possible. Mounted internally.
One Raymarine simple Depth numeric, aft port. This is mounted (thru hull) approx 4m from the other Raymarine  sounder transducer. This appears to be enough to avoid mutual interference,  at least at depths <10m, even with keel up.

One NASA Clipper aft port. Mounted internally.
The NASA and Raymarine at aft port are within 1m of each other.  They use different frequencies, so no interference...so far...

Distance between inner and outer skins - the foam core-  on my boat appx 15mm. YOURS MAY VARY!

Tip. Shorten the pilot drill on the hole Cutter to the very minimum  possible, and be VERY careful. Slow speed.

Tip. Use "slow" epoxy to back fill the excavated hole for the internal pad. The resulting D50mm x 18mm thick "puck"  cast into the hull made using "fast" epoxy on my first one got too hot (even mid winter) and set with entrapped bubbles. Not good for sounder performance.
I remade it with slow epoxy.

Antifouling .
After seeking advice, and testing on an old, dead, airmar transducer...my conventional antifoul appears to not "melt" the one external Airmar sounder head, and once painted it reads the same depth as the new internal fish finder.

All 3 tally D to a max of 10m, so far.

[Graham W]

A couple of miscellaneous points:
As Simon notes, depth transducers with different operating frequencies shouldn't interfere with one another, even in reasonably close proximity on the same boat.  My Cruzpro  is 120 kHz and the Nasa Clipper is 150 kHz, compared to 50 or 200 kHz (or both) often used by Airmar (Garmin, Raymarine etc). The higher the frequency, the better that it can cope with the shallows.

It may just be a marketing ploy (which I've fallen for) to get you to spend a lot of money on a tiny bottle of chemicals but there is water-based anti-fouling paint specifically for coating plastic transducers https://seamarknunn.com/products/marlin-echo-antifoul-70ml-transducer-paint-black.  They claim that normal anti-fouling may not only dissolve transducer plastic but also reduce its signal.

[Sea Simon]

Good points GW, thanks.

Antifouling sounder heads.
Perhaps "solvent based paints" are not what they were,  when Airmar wrote their instructions?
... (like many things these days, me included!) Probably less VOCs?

I've  recently found it necessary to buy more additional solvents than in the past, including Acetone, Xylene and "2 pack poly thinners" (whatever they may be?). Hardly seems like progress, as my shed now contains even more cans of half used "potions"

I tested on my dead Airmar sensor head, which is very hard plastic, almost akin to "bakelite"?
I've not tested the NASA Clipper head which appears softer.