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Old 16-12-2012, 03:52   #1
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Brilliant Idea from Dashew

I was reading this:


SetSail» Blog Archive » Cruising With NMEA 2000 – A First Hand Look The Maretron System, And A Few Other Observations

And noticed that Dashew is using water pump">raw water pump temps as a proxy for raw water flow. What a great idea! A $20 under-bolt temperature sensor is all you need in a N2K system.

I think I'll be doing that on my new system, for both main engine and genset. Obviously, it won't tell you anything once the impeller blades have disintegrated, but you'll get a sharp warning some time before that happens.

He's also measuring exhaust elbow temps. I'm less clear about how he does that -- maybe he just brazed a tab on the elbows.
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Old 16-12-2012, 04:08   #2
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Re: Brilliant Idea from Dashew

I think I might stick one of these on my main engine exhaust elbow, if I can figure out how to do it. My exhaust elbow is a massive piece of solid, shiny stainless steel. I don't quite imagine how to attach the sensor other than jubilee-clipping it on (hose-clamping it on). Maybe there's some kind of heat-conducting epoxy I could use? I don't fancy taking it off and having it welded.
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Old 16-12-2012, 05:54   #3
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Re: Brilliant Idea from Dashew

Not saying all this information doesn't have a use, but doesn't it seem a little paranoid and where would it end? I have occasionally thought that a flow switch would be useful in the engine supply line (but haven't worried about it enough to research it).

PS - I wouldn't weld that elbow, at last to start with. Do an easy method, the clamp or a drilled/tapped fitting.
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Old 16-12-2012, 06:01   #4
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I have always been stunned that we don't instrument raw water flow and that we live with the resulting impellor failure. A 5-10k engine and no manufacturer fits a 50 dollar sensor.

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Old 16-12-2012, 06:12   #5
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Re: Brilliant Idea from Dashew

How are the temp sensors interfaced to N2K?
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Old 16-12-2012, 10:37   #6
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Re: Brilliant Idea from Dashew

A normally open snap switch rated at 200 degrees f. hose clamped to the exhaust elbow and connected to the engine alarm circuit in parallel with the oil pressure alarm sensor is a simple and cheap way to get your attention.
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Old 16-12-2012, 10:55   #7
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Re: Brilliant Idea from Dashew

Quote:
Originally Posted by Dockhead View Post
I think I might stick one of these on my main engine exhaust elbow, if I can figure out how to do it. My exhaust elbow is a massive piece of solid, shiny stainless steel. I don't quite imagine how to attach the sensor other than jubilee-clipping it on (hose-clamping it on). Maybe there's some kind of heat-conducting epoxy I could use? I don't fancy taking it off and having it welded.
You can buy metal "snap disc" thermostats in various temperature ratings from places like Grainger. Put it on your metal exhaust elbow and wire it to a piezo alarm. I did that on my little diesel 12 v gensets I made. Cant remember for sure but think I used the 180-200 degree version...
3F11-100 - WHITE RODGERS - DISC THERMOSTAT, SNAP ACTION | Newark
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Old 16-12-2012, 11:13   #8
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Re: Brilliant Idea from Dashew

Quote:
Originally Posted by Don Lucas View Post
Not saying all this information doesn't have a use, but doesn't it seem a little paranoid and where would it end? I have occasionally thought that a flow switch would be useful in the engine supply line (but haven't worried about it enough to research it).

PS - I wouldn't weld that elbow, at last to start with. Do an easy method, the clamp or a drilled/tapped fitting.
I don't anyone would say that the fact that your exhaust is just about to burn down from lack of raw water flow is "too much information" . I think actually that it is absolutely fundamental. Raw water flow interruption is a common problem, bad impeller, baggie in your seawater strainer, and you usually only find out about it when the exhaust is burning through (which can sink you, on top of the other damage) and your engine is already overheated. Yes, I d*mend well want early warning, and think everyone needs it. It baffles me that all boats aren't delivered with such an alarm.
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Old 16-12-2012, 11:15   #9
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Re: Brilliant Idea from Dashew

Quote:
Originally Posted by Paul L View Post
How are the temp sensors interfaced to N2K?
Maretron makes a temp module which will read four temp probes and two pyrometers, and feed all this data into the network.
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Old 16-12-2012, 11:19   #10
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Re: Brilliant Idea from Dashew

Quote:
Originally Posted by Cheechako View Post
You can buy metal "snap disc" thermostats in various temperature ratings from places like Grainger. Put it on your metal exhaust elbow and wire it to a piezo alarm. I did that on my little diesel 12 v gensets I made. Cant remember for sure but think I used the 180-200 degree version...
They are good idea.
The circuit is very simple. Use a digital thermometer to measure the normal running temperature and select a thermostat with a rating just above this. Or they a cheap enough to buy a few and try them till you find the lowest value that does not trigger.

However I think A digital readout of multiple temperatures is great. I am a gadget freak and love all this information, but a word of warning many people never look at gauges, so an alarm backup is a not a bad idea.

When you have multiple gauges reading temperatures in different areas its easy to loose track of what is normal. A trick we used in experimental aircraft was to rotate the gauge so that 12 oclock represented "normal". A whole bank of gauges could therefore be scanned and anything out of the ordinary immediately stood out.
These display ergonomics become important if gauges are to provide worthwhile warning of abnormal conditions.
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Old 16-12-2012, 11:37   #11
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Re: Brilliant Idea from Dashew

I've got the excess water flow routed into a cockpit drain that is right next to the helm position. It makes a distictive (water flowing in a pipe) sound when the water is flowing. Works well. Simple.
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Old 16-12-2012, 11:41   #12
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Re: Brilliant Idea from Dashew

A couple of other options
EX-1 and
Wet Exhaust Temperature Alarm by Borel Manufacturing Inc.
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Old 16-12-2012, 12:03   #13
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Re: Brilliant Idea from Dashew

Exhaust temp is critical. Most Diesel engine manufacturers will measure it under various conditions on a new build before they certify the engine/application. (usually larger engines)
The snap disc is a good emergency warning though.
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Old 16-12-2012, 12:19   #14
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Re: Brilliant Idea from Dashew

This is the kind I would suggest although I don't think this particular one is N2K.

http://www.halyard.eu.com/Downloads/...t%20System.pdf
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