Transducer Cable Splicing

[barfwinkle]

Good morning to all

Okay wise sages, heres the question of the day (in my little corner of the world).

I have a new transducer (P79 Airmar) that has a Garmin 6 pin cable. The end that connects to the 441s (female end) WILL NOT snake through the appropriate space. Somewhere in the literature (online or documents) I saw a not about splicing the cable. It said not to without a proprietary "weather proof box" that I assume Airmar Technologies sells. While un-installing the old transducer (for a Garmin 128) I decided to just cut the plug off and see what I found. The old plug is an RCA male plug and the cable has three wires, one stranded/twisted bare wire (18 gauge maybe) and two insulated wires (maybe 22 gauge), all wrapped in a metallic foil type shield.

The new transducer has a 6 pin Garmin plug BUT there are only 3 of the 6 holes in the plug that are wired. The new transducer also came with 40 or 50 feet of cable and I will be using about 6 feet maybe(?) so splicing the cable sounds good to me! I know that splicing creates an opportunity for foul play somewhere down the line, but it would sure be nice to get rid of about 35 feet of cable.

Has anyone ever done this or do you have comments/suggestions?

TIA and Fair winds.

[Oswego John]

Hi Bill,

I wish that I had a niclel for every electrical/electronic splice that I made in the past. Some were made in W.P. boxes, but the vast majority weren't. Most were made under government specs.

The splices were made in varying weather and temperature conditions , from the cold of the Arctic Circle to the intense desert heat of the nuclear test sites in Nevada.

Briefly, the conductor splices are made, whether by crimp, solder or mechanical means. After individual isolation and insulation, the splice package as a whole was wrapped in vinyl electrical tape as per specs.

Then the entire splice was coated with 3M Scotchkote liquid electrical insulation. An applicator brush is attached inside of the screw cap. It dries fast so I generally applied two or three coats of weatherproofing over all.

There are other brands of coating on the market but I generally stuck to 3M products and never regretted the decision. A half of a pint will sit on the shelf for years on end.

Fair warning: When using this product, wear your oldest of old clothing. 3M Scotchkote has the ability to leap over three feet sideways and permanently attach itself to anything, clothing included, that may be in the area. This attachment is FOREVER.

Personally, I don't like extra conductor coiled up. I once inadvertantly created a choke coil without realizing it.

Good luck,
O J

[barfwinkle]

Thanks OJ, and fwiw, Airmar told me it was ok to cut some of the cable and then splice, but that I should leave at least 10 feet or there was the possibility of changing the impedance, which would effect the transducer's accuracy. Who knew?

And I was correct, the little box that they want you to use cost 45 smackers!

fair winds

[Squid]

Just experienced similar issue with the new Garmin anemometer. We just cut and spliced get to the reading unit (GMI) at the helm pod. The previous recommendations by OJ appear very sound. Believe it's an issue of the manufacturer covering their six. No issues yet on the new install.... Good question since the transducer will be my next hurdle. I currently have a speed sensor going through the port side of the keel (bilge) and the current transducer (not through hull) up forward under the forward berth. The issue I am trying to figure out is; do I stay with two sensors (speed temp on port keel, depth forward no new hole), or go to one sensor forward under the forward berth and put a new through hull into the boat. This would be one of the new smart sensors with speed, temp, depth into one unit. The motive being as I replace the old ST-50 stuff move to Garmin (NMEA -2k). Just not sure I like placing a new hole into the hull if I may not need to.

[John Danicic]

I had good luck splicing my speed meter with a waterproof junction box. Also the Wind indicator as well and that one is in the bilge next to the foot of the mast.

Just make sure you correctly splice all the wires to the same colors, (wear your glasses and use a strong work light), even splice the bare metal "dump wire" that is included in the bundle. Can't say for sure it you have to do that but it doesn't hurt.

I used one of these

You can get it from Defender for about $22.00. Being in freshwater, I found that I could get away with going to a Radio Shack or a electronics store and just buy the plastic connector bar for under a few dollars. Just put the bar in a place that won't get wet or make your own box. I use these bars for connecting the VFH Radio to the NMEA outputs from the GPS, auto helm, wind instruments and all the other goodies that require many tiny wires to be connected so that they can speak their mystical language to each other thereby telling us way more then we need to know. Ah, the modern age.

[Keith]

The problem with going from a shielded cable to a terminal block shown in the picture is that you loose the shielding protection for distance that you removed the shield. Without getting to technical depending on the frequencies being transmitted this can cause cross talk, signal integrity loss, electromagnetic interference from the alternator and other electronic devices, etc.... I.E. It could very well screw up the readings at the monitor. They shield cables for a reason. Also earlier someone mention a change of impedance due to shortening the cable. This can also be a problem.

Bottom line if you must cut the connector off to snake it through the boat. Do so right at the connector end. Then simply re-terminate a new connector and ensure the you terminate the shield to the connector shell. Coil up and excess cable in an out of the way place. If the manufacture says that cable length will no effect the functioning of the instrument then by all means cut it to the desired length and re-terminate as described above.

I've spent a life time in the cable and connector industry. Hope this helps and doesn't confuse more!

[Steve Laume]

Squid, I would stay with the dual location as you have it unless you wanted to move everything to the aft location. Having the depth transducer as far forward has some advantage but this is not the case for the speed and temp sensors. If you tried to mount everything up forward with a through hull You would need a huge fairing block where smooth water flow is very important.

On Raven I was able to keep the full length of transducer cable with a neatly coiled bit of wire tied under the settee. I needed to splice my radar cable to be able to pull the mast. This was done in a metal junction box much like the one in the former post. It is my understanding that the metal serves the same function as the cable shielding. The radar has always worked well and I have not noticed any interference with other devices, or vices for that matter, Steve.

[Squid]

Steve,
Thanks and understand... My other post "winter projects", one of the main jobs that started the entire goat rope was the need to replace the anemometer cable for the new Garmin.. and the topside penetration was not done correctly by one of the previous owners. So, we moved all the termination to a small fabricated box beneath the mast inside the head... Looks fine/works. Also filled all the old holes and placed in a proper compression through hull for the cabling.
I agree with your suggestion on two sensors. When they are replaced (next is depth) I think I will replace the forward on hull transducer that shoots through the hull with the required Garmin device (actually they all use Airmar), and the newer speed/temp out the same spot as the current speed sensor... NO NEW holes in the hull and all works well.... no fairing. Thank you "very" much for the note. Always like verification on the logic.

[Hummel]

Hi

I installed the Airmar 79 transducer last season along with the Garmin 740s.

Splicing did not create a problem. My spice was close to the unit and in a waterproof Navpod box.

By th eway the tranducers works great. Easy install.

Good luck

Jim

[barfwinkle]

Thanks to everyone for their input.

Fair Winds

[barfwinkle]

The deed is done and to two components are talking. The "marineized" thingy I got was a bit pricey, but its waterproof. FWIW a buss bar (with a cover) would have been just fine.

Now if I can only get Einstein to talk to Gretrude all will be well.

Fair Winds