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Author Topic:   Splicing SONAR and GPS Cables
RickS posted 06-13-2006 03:44 PM ET (US)   Profile for RickS   Send Email to RickS  
I am about to install my new Lowrance LCX 26c GPS/FF on my 2005 21 Outrage. The NEMA 2000 plugs on the transducer cables and GPS antenna are huge and the installation guide recommends drilling 1-inch holes for them to pass through. I was going to cut them off, drill much smaller 1/4-inch hoels ,run the cables without the ends and splice them back under the center console. Can this be done?
Parrot6909 posted 06-13-2006 07:15 PM ET (US)     Profile for Parrot6909    
I am not a huge proponent of cutting and splicing. It is one more connection to fail. I just installed a M68C which required the same size hole but the unit covered the hole in the console. I'd keep the wire intact if it were me.
Salty posted 06-13-2006 07:31 PM ET (US)     Profile for Salty  Send Email to Salty     
Don't splice. You'll always have that weak point. I've done it and it always comes back to be a problem. I'm about to put in a Lowrance too. A 1-inch hole isn't bad. Good luck.
RickS posted 06-13-2006 09:55 PM ET (US)     Profile for RickS  Send Email to RickS     
Did you put the 1-inch hole in the splashwell? What did you cover it with?

Will that huge connector pull though the [rigging tunnel] from the bilge into the center console using the pull line? Thanks for any help.

jimh posted 06-13-2006 10:58 PM ET (US)     Profile for jimh  Send Email to jimh     
It would be better to just remove the connector, run the cable through a smaller hole, and then re-install the connector. If the connector is a molded-on connector this may not be possible.

I am confused by your description of the cables. If these cables are really NMEA-2000 drop cables from the device to the data bus, there is no big problem with splicing the cables as far as the electrical signals go. The wires in a NMEA-2000 drop cable are just two twisted pairs. One pair carries battery voltage; the other pair is a differential data pair. If you make a decent splice it should not be a problem. If these are not NMEA-2000 drop cables but are instead direct connections of a SONAR transducer to the sounder and a microwave antenna to a receiver, then I do not think it is a good idea to make splices in them. The electrical nature of the signals these cables are carrying may be affected by the discontinuity of a splice, as these devices often use a transmission line technique for sending the signal down the cable. The cable has a characteristic surge impedance, and a splice will disrupt that characteristic impedance.

Howver, I do not recommend the installation technique you are suggesting, and my objection is not at all to do with the notion of a splice being something awful. The problem with an installation as you are suggesting is that the cable and device become captive. You cannot remove the device from the boat (say for service or repair) because it cannot pass through the bulkhead without cutting apart the connector again. That is not a great way to install things.

If you must cut a 1-inch hole in the helm console to admit these cables, try to locate the hole in a place where it will be inconspicuous, and try to cover the hole with some type of shield so that rain water and spray will not easily enter the hole. A PERKO clamshell fitting makes a good cover for a hole like that. If the console surface is sloping, orient the PERKO clamshell so the open end is on the lower slope. This should keep most spray and rain out of the hole.

I need to follow my own advice on my console. I, too, have a LOWRANCE sounder and a two 1-inch diameter holes in the console surface (made by the previous owner). These don't have clamshell covers at the moment, and when there is heavy rain or spray, water can run into the interior of the console through these large holes.

jimh posted 06-13-2006 11:43 PM ET (US)     Profile for jimh  Send Email to jimh     
According to the LOWRANCE instruction manual, the recommended hole size to pass the SONAR connector is 7/8-inch, not 1-inch. Cf.: LCX-110C_LCX111CHD_LCX-25C_LCX-26CHD0151-311_030705.pdf --Page 26.

jimh posted 06-14-2006 12:03 AM ET (US)     Profile for jimh  Send Email to jimh     
If the wiring diagrams are shown to scale, it looks like the POWER connector is larger than either the SONAR transducer connector or the NMEA-2000 cable from the GPS-2000 NMEA-200) device. That will mean your console hole will have to be larger, perhaps even more than 1-inch

As for the bulkhead holes, I understand your preference to not drill a large hole for the GPS lead-in. However, it does look like the GPS device will cover the hole used to pass the cable through a deck if you use the pole mount adapter.

The owner's manual does mention a 1-inch hole for the connector on the LGC-2000. (Page 2). I agree--that is a big and ugly hole.

This cable is a NMEA-2000 cable so you could splice it without too much concern. It is just power and data as I mentioned above. If you have to route the cable through a lot of bulkheads, I agree it would be better than drilling a big, ugly 1-inch hole through all those bulkheads.

swist posted 06-14-2006 10:17 AM ET (US)     Profile for swist  Send Email to swist     
One other point. On some types of electronics, the length of the cable and associated impedance, resistance and/or capacitance has been taken into account in the readings produced. If you do splice a cable (which I don't recommend either), don't mess up even more by using it as an opportunity to discard excess cable length.

I do sympathize with the original poster. I've installed a lot of marine electronics, and sometimes the connectors do seem unnecessarily large for the size of the cable.

bsmotril posted 06-14-2006 11:37 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
The cable Caps made by Big John are ideal for covering up these types of holes. Pictures at the link below. West Marine and BoatUSA carry them in stock at my local stores.


bsmotril posted 06-14-2006 11:38 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Here's a better link showing the various caps avaailable.
RickS posted 06-14-2006 10:55 PM ET (US)     Profile for RickS  Send Email to RickS     
I was really hoping for a nice clean transducer mount like the factory job on this 2006 21 Outrage, but those cable caps look like a great idea to keep me from splicing. P.S. check out last week's transom repair I did on my 9-foot project boat for the kids, also on the same site. Thanks for all the great input.
aquaman posted 06-15-2006 12:04 AM ET (US)     Profile for aquaman  Send Email to aquaman     
Rick--I just completed installation of an LCX26C on a friend's Grady. I can tell you I had succes in removing the connector from the ends. The pins will stay on the cable. Be very careful and remember how it is oriented. It will only go back on one way but all the pins need to be lined up correctly. Add a small dab of glue and the connector will stay on. I think you'll end up drilling a 3/8" hole.


jimh posted 06-15-2006 08:49 AM ET (US)     Profile for jimh  Send Email to jimh     
John--Your suggestion of removing the pins from the connection is a good one. I assume they are back-loaded into the connector shell and you can get them to release by slightly compressing them. Did you happen to have a special tool to accomplish this? Often you can make the job of unloading the connector pins easier if you have the right little tool for it.
aquaman posted 06-15-2006 01:21 PM ET (US)     Profile for aquaman  Send Email to aquaman     

No special tool, just a wood dowel sized appropriately. I gave the pins a very light push and out they came. You might think of it as an inner plug housing holding the pins in place. When putting it back together the inner plugh slides back into the connector.



jimh posted 06-15-2006 02:02 PM ET (US)     Profile for jimh  Send Email to jimh     
It sounds like you slid the connector insert out of the connector shell. I have not seen one of these LOWRANCE connectors in person, yet. Many connectors can back-load the connector insert into the connector shell. That sounds like a better approach than actually removing the indivual pins. The insert is usually keyed so that there is only one way to insert it into the connector shell.
RickS posted 06-15-2006 03:23 PM ET (US)     Profile for RickS  Send Email to RickS     
Here is a good picture of the cables. This is my weekend to install it all. Will let you know how it worked out.
aquaman posted 06-16-2006 12:22 AM ET (US)     Profile for aquaman  Send Email to aquaman     

You've got it exactly right and the insert is keyed to the connector. You also did a much better job of explaining it.


RickS posted 06-20-2006 11:18 AM ET (US)     Profile for RickS  Send Email to RickS     
Now I know why the dealer wanted $1000.00 to install the electronics. It took most of the whole weekend.
I was unable to remove the cable connectors as John suggested, prehaps the ends were different. The Big Jon cable cap, however, worked great as a coverup for the 1" transom hole and it looks very clean. There was also no way I could pull those cable connectors through the rigging tunnel so I fished a new line over the gas tank and up into the center console through the boot without too much trouble.
Unfortunately, the GPS antenna connector was just to big to go through the T-top tubing. After multiple attempts, the line got cut and then soldered back together. The VHF end had to be soldered on also so it just took a little more time. One neat trick to running the wires in the T-Top was to use a nut tied to fishing line and a large magnet outside the tubing to guide it where I needed it to go. By the end of Sunday, the console was cut, the GPS/FF and VHF flush mounted, antennas were on the T-Top, everything wired together, the VHF interface to the GPS done and, thank goodness, it all worked! Happy Fathers Day! Thanks for all the suggestions.
aquaman posted 06-24-2006 12:44 AM ET (US)     Profile for aquaman  Send Email to aquaman     

Sorry to hear you could not remove the connectors. I did have to work pretty hard to get them off.


jimh posted 06-24-2006 06:48 AM ET (US)     Profile for jimh  Send Email to jimh     
That is a very good idea to use a magnet, nut, and fishing line!

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