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Old 09-02-2011, 18:44   #1
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Integrated Electronics and All Your Eggs in One Basket

What is the redundancy or backup for integrated electronic systems that all share the same network? I have been wondering about this and would like to pose a few questions for anyone who would like to jump in.

My background is in aviation where integrated electronics has become common but not without two or more degrees of redundancy or backup at every level. Essential instruments have their own network and are not allowed on the main network. Is there any such thing in the design of marine integrated electronics network?

For example, a NMEA 2000 network is a four wire cable with two signal wires and two power wires for all the instruments on the bus. If the power wires loose power, then everything goes dead? True? Is anyone installing these networks with alternative power source or are there any networks that make a provision for this?

I see these networks sometimes go up the mast to masthead instruments. If you get dismasted then what? Wouldn't that also break the network cable and cause you to loose position, heading, radar, autopilot and maybe even engine instruments?

Do those of you with these systems still have a magnetic compass?

Is is possible for a device, connector, terminator or something on the network to fail and bring everything down with it? How do you troubleshoot this or is anyone installing these systems with some kind of redundancy and what is that?

Do you carry spare parts for the network? Spare cable, connectors, terminator resistors, etc?

Do these networks have any kind of built-in lightning protection? Are they being installed with external lightning protection?

What if the boat takes on water? Is the routing of the network cable and all the exposed connectors (i.e. N2K depth sounder sensor) immune to this?

It looks to me like an increasing number of boats are being equipped with these integrated systems and nothing else. If anyone has given any thought to this, I'd like to hear your reasoning.
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Old 09-02-2011, 18:59   #2
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No significant provision for backup or repair of the built-in instruments here. No redundancy. Unlike avionics, yacht system failures usually have time and access advantages. There is time, lots of it, to work around any problem. Plus, there is relatively easy access to repairing systems or creating alternatives.

There are only a few minutes in a year of cruising where I'd really rather the instruments remained functional. Those would be while transiting some reef areas or for transiting, for example, the foggy Golden Gate entrance. Even in those few moments there are reasonably adequate alternatives such as standing bow watch, listening to foghorns, or turning around, or anchoring to effect a repair.
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Old 09-02-2011, 20:31   #3
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Interesting.

Should we buy instruments that are so interdependent they cannot function alone?

And is redundancy provided by our skills as sailors, rather than our majic boxes?
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Old 09-02-2011, 20:33   #4
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That's a perfect answer daddle. And, for a hundred and twenty bucks, you can get a handheld gps which will allow you to plot your position on a chart as backup.
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Old 09-02-2011, 21:27   #5
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Funnily enough, I have a 1993 Trimble aviation GPS sitting in a bag in my pilothouse. It's merely lat/lon and a couple of airplane-related outputs, but I hesitate to throw out even the most elderly of handheld (sort of...it looks like a grey phaser from Star Trek) GPSes until it's well and truly dead.
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Old 09-02-2011, 23:18   #6
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Quote:
Originally Posted by North26West80 View Post
What is the redundancy or backup for integrated electronic systems that all share the same network?
Current Boat-Handeld GPS and paper charts, no redundancy.
New Boat (soon)- Full integration, redundancy is what current boat has.

There is a great argument for independant systems for the reason you state. However I find that the integrated systems are so neat and compact in the nav station and amazing to use that I'm going that way. When it all goes Kaput please be nice and don't say "I told you so".

Greg
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Old 10-02-2011, 06:14   #7
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Making your network a lightning rod.

Let me elaborate. One of the nifty things an integrated system can do is compute true wind from apparent wind if the mast-top wind speed and direction is integrated. And the new solid state mast top instruments are appealing to eliminate moving parts up there and bird perches. (A few years ago when my mast was down I prewired a N2K cable up there in anticipation of this day.) But if I do this, am I not turning the backbone of my system into essentially a lightning rod? The network cable will go right to the highest point on the boat. Doesn't seem like such a good idea especially here in Florida. Comments?
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