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Between chart plotters

Ward H

Nov 7, 2011
Catalina 30 Mk II Barnegat, NJ
My i70 instruments and EV-100 auto pilot uses the internal Axiom 7 GPS for all of their functions. My Standard Horizon radio uses an external GPS, IIRC it is required, which is located in the quarter berth. I like the redundency of two GPS sources, not that it is likely I would ever benefit from having two.
Jun 25, 2004
Hunter 306 Pasadena MD
So this is now about the new goal of (maybe) installing an Axiom 9 and a SeaTalk to SeaTalkng converter myself. I opened up the lower steering pedestal instrument pod, which contains the speed/depth/wind/autopilot, all 2004 generation Raymarine units using the SeaTalk1 bus. Here's what that looks like:
The middle instrument of the 5 is the compass. The small black box on the right turns out to be a Hunter-installed cheapo thing to split an incoming white SeaTalk wire into 3 outgoing Seatalk wires for 3 of the 4 instruments. The 4th instrument daisy-chains to one of the others to get its SeaTalk.

The upper Navpod contains just the old C80 plotter, which gets power, SeaTalk1, and NMEA0183, going from left to right:
The first mystery is that the black SeaTalk1 cable in the plotter Navpod disappears into the pedestal tube going down, and the white cable in the lower pod (which has to carry all the SeaTalk information) disappears into a lower hole in the same pedestal tube. Where do they join up? Who knows? The only other networked things are a fluxgate compass that's down in the aft cabin, and a GPS unit mounted on the stern. I'm 80% sure that the old GPS unit connects to the plotter through a thin, 2-core wire that is spliced to the NMEA cable going to the plotter.

Anyway, I'd like to install a network based on this diagram from the SeaTalk to SeaTalkng converter (E22158):
Screen Shot 2021-08-05 at 7.51.23 PM.png
which says the converter would be powered by the old SeaTalk network. The only SeaTalkng device in the new system would be the new Axiom 9. Based on the fact that the fuse at the 12V panel for the C80 is only a 5A fuse,
but the Axiom calls for a 7A fused circuit, I think I probably have to run a new power cable all the way from panel to Navpod. (For that matter, the manual for the old C80 calls for a 10A circuit, so... why this didn't start a fire before, I don't know.) Given that there's no room on the left-hand loop of the pedestal guard (where all the current wires are), I guess I can run the new power cable on the right-hand side, drilling new holes in the pedestal tubing.

I guess I can also run a Seatalkng cable from upper Navpod, down the right-side tube to the lower pod, and put the SeaTalk/SeaTalkng converter down in the lower pod. This would leave me with having to run one long power cord all the way to the panel, but the one network cable only a couple of feet. Or I could cut the end off the SeaTalk cord currently going to the plotter, splice in a SeaTalk1 cable to go to the converter, and put the converter up in the Navpod. So I'd only have to run the power cable...

Oct 26, 2008
Catalina 320 Barnegat, NJ
I'm in the dark about the Seatalk/Seatalkng conversion discussion, but it would seem to be pretty straightforward assuming there are manuals to describe the connections.

I'm not following why you think it is necessary to run a new power cable. What gauge is the existing? The fuses are an easy change. To protect the wire (prevent a fire) you only need to size the fuse for the capacity of the wire. A 16 AWG wire for a simple run probably can be protected by a 15 amp fuse on your electric panel. Electronics often need to be protected by a lesser fuse (to protect the electronics, not the wire that supplies the power). That is why there is often an in-line fuse holder that comes with the instrument that holds a smaller fuse.

I do not like to run wires through the boat that are less than 16 AWG, so I am comfortable with 15 amp breakers at the electric panel (if you have a longer run with a 16 AWG wire, you may have to increase the fuse or breaker because length adds resistance). The Axiom needs to be protected with a 7 amp fuse. You can install the 7 amp fuse in-line at the nav pod station if you have a larger fuse or breaker at the elec panel. But since you have a 5 amp fuse there already, just replace the fuse and put a 7 amp fuse. IF you are worried about the wire, then check the gauge. If the wire is large enough already, then you have no worries.

The basic premise is: fuses or breakers at the 12V panel are sized to protect the wire. The fuse (or breaker) rating should not exceed the capacity of the wire, which should be sized based on the anticipated amperage load and length. Fuses that are connected with electronics and various sensors are sized to protect the electronics. A larger current in the wire may not necessarily overload the wire, but it could damage the instruments. When you are installing fuses, know what you need to protect and where it needs to be protected. Typically, fuses are placed where the wire gauge is downsized, and at or in close proximity to battery terminals.
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Jan 15, 2006
Macgregor 22 Silverton
"A larger current in the wire may not necessarily overload the wire, but it could damage the instruments." Said somewhat backwards I think. A smaller fuse at the device limits the amount of current available that can flow into the device in a given amount of time.
Oct 26, 2008
Catalina 320 Barnegat, NJ
Well @LloydB , my point was that @jaysweet seems to be concerned about the wire (and he wants to replace it) just because there is a small 5 amp fuse on it. The 5 amp fuse is there to limit the current into the electronic device just as you said. The wire probably doesn't need that much protection. I don't know for sure because I don't know the wire gauge. But I suspect that if he has a power source to the original chartplotter, he probably doesn't need to replace the wires (positive & negative) just because there is a 5 amp fuse on it. Just change the fuse at the electrical panel to an appropriate size. The new chartplotter probably comes with the correct fuse already in-line on the lead at that end. I would probably just install a larger fuse at the electrical panel (sized appropriately for the wire, not the instrument).
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