Using a switch to change depth gauges on single sensor?

[MikeP]

My two Garmin chartplotters (lower Helm and FB) share depth data through the Garmin network. I have a separate Raymarine ST40 depth gauge on the FB Helm with it's own transducer as a back up but do not have one at the lower helm. I would like backups in both positions but don't want to install a third transducer and was thinking about purchasing another ST40 display and simply using an SPDT switch to select which display is connected to the transducer.

But I'm wondering if splicing a switch into the transducer feed will have any ill affect on the that signal as far as shielding or any other issues. Depth sounder makers states that the transducer wire should not be cut if it is too long, just rolled up. So I'm wondering if there is REALLY a problem with that or they are just being cautious to ensure nobody sues them if a mechanic cuts/incorrectly wires a connection which results in faulty depth.

 

[rsmith]

Don't know about the Ray. but I spliced 2 Datamarine units off the same xducer and work fine even if both are on at the same time.

 

[z28jimi]

I wanted to replace my Datamarine speed log wheel with a new Garmin depth transducer. Yard monkey cut the wire to the Datamarine depth transducer instead, then realized his error. Wanted to keep Datamarine depth gauge as a backup to the Garmin, so I called DMI and they told me to told me to just splice the wires, including the shielding, and should be OK. Did so, and Datamarine depth consistently reads within a tenth or so of the Garmin depth reading.

 

[Boatsb]

Mike the shield is a problem with a standard switch. You need a switch that carries the shield too. FWIW why do you need this? Is the garmin unreliable?

 

[Boatnut]

Not to argue with Scott, as using a good quality switch and switching both the signal portion and the shield will certainly work. However, you are feeding two signals to a common point. The shield are common to both transducers at the connector on the main unit., you should not have to switch the shield, only the center conductor. I have never opened up one of these cables, but I have repaired many a shielded cable on video and ultrasound equipment. It there are 2 conductors plus a shield, be sure to switch both wires, there would be no need to switch the shield if this be the case.

 

[petewentsailing]

If I am reading your post correctly, 2 ST40's can run off one transducer, no problem. I have done this twice. The second Raymarine ST40 is connected to the first using the SeaTalk port on the back of each unit. In the manual, there are instructions for setting the second unit as a repeater, rather than a stand alone depth sounder. It's pretty simple, and you can avoid any splicing, switch, etc.

 

[MikeP]

"FWIW why do you need this? Is the garmin unreliable?"

No, the Garmin has been fine. I did have an occasion a few years ago where it quit reading depth. It turned out to be a loose connection. But it was rather traumatic to have no depth reading and that's when I installed the ST40/separate transducer. I installed it at the upper helm though I'm not sure why - we actually operate the boat more often from the lower helm. I must have had a good reason for that at the time but for the life of me I can't think what it was!

"If I am reading your post correctly, 2 ST40's can run off one transducer, no problem. "

Thanks, I didn't even think about the sea talk thing. Since I only installed the DF/transducer with no intention of ever linking any Raymarine equipment, I didn't really read/pay attention to that at all in the manual originally. I did wonder about it a few days ago but I figured it would require some sort of network box which I don't care to buy just for a pair of backup DFs. But if it just requires a cable between the displays (no additional box), I'd better pull out the manual and actually read that section!

 

[SeaEric]

If I recall correctly from (15 years ago) when I had a similar setup, to work as you want it to between 2 depth displays - the seatalk cable has to have DC power to it from somewhere.