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Old 02-19-2015, 11:30 AM   #21
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Sight tubes in the engine room are a weak spot for fires IMHO . They may get brittle of crack and voila you could have a problem . I just have a good dip stick handy , doesn't hurt to put some water paste on it once and a while too for an added bonus . Of course some tanks you can't dip .
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Old 02-19-2015, 01:57 PM   #22
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I think the only way a sight tube on a diesel tank could be a fire hazard is if you already have a fire going. If a sight tube cracks or breaks under normal circumstances all that will happen is a few cups of fuel will end up in the bilge. This is assuming, of course, that the operator is smart enough to keep the valves on the sight tube closed at all times other than when checking the amount of fuel in the tank.
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Old 02-19-2015, 03:01 PM   #23
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I think the only way a sight tube on a diesel tank could be a fire hazard is if you already have a fire going. If a sight tube cracks or breaks under normal circumstances all that will happen is a few cups of fuel will end up in the bilge. This is assuming, of course, that the operator is smart enough to keep the valves on the sight tube closed at all times other than when checking the amount of fuel in the tank.
Actually, if true 'gauge cocks' are used in the sight tube installation, the lower valve contains a ball-check valve to prevent fluid from escaping if the tube is broken. It also provides a drain for servicing. Penberthy is one of the popular suppliers. The valves are sold in upper/lower sets. An added benefit is that they have 4 ears that allow ss guard rods to be installed to protect the tubes. A little expensive, but in the grand scheme of things, fly stuff.



As Marin stated though, best practice is to run with the valves closed, at least the lower valves.

I gotta try to remember that one . . . . . . . like seacocks
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Old 02-19-2015, 03:11 PM   #24
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For those leery of sight gauges, but have fuel fills not straight enough for a hard dip stick can possibly use a sounding tape.

It's nothing more than a very flexible tape measure with a weight on it.
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Old 02-21-2015, 07:23 AM   #25
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IF a stick or tape can be used to read a tank, remember there are shmeer on compounds that will tell you how deep the water in the bottom of the tank is.

Many fuel pickups are raised a couple of inches , so one never knows till the water gets rough.
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Old 02-21-2015, 09:25 AM   #26
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Check the position of the valves, off, as they should be except when checking the fuel level. Then open, check the level and close. I guess spring loaded, turn to open, close automatically valves may available.
In a fire this tube will surely melt but probably so will the engine supply and return hoses and their valves will usually be open, not to mention the jugs of engine oil.
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Old 02-21-2015, 10:11 AM   #27
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I guess spring loaded, turn to open, close automatically valves may available.
"Push" to open valves have been around for a long time. The photo below is 7 years old.
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Old 02-21-2015, 11:04 AM   #28
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Those simple arm type gauges are actually fairly accurate if you know how to use them. What they are really is repeatable. that is every time the fuel is the same level in the tank they will give the same readout.
Mine were marked in 1/8 tank intervals but it was easy to interpolate to 1/16 tank. Knowing the tank capacity I could figure how much fuel was used. The key was to calibrate the gauges as I filled the tanks. e.g. If they read half full I would measure how much fuel it took to fill them form that point on it always took the same amount from half full.


You can easily do the same from any level . Then I could easily predict how much fuel I needed or how much fuel I had used on a trip. Lots simpler and cheaper than flow scans and good enough for me.
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Old 02-21-2015, 11:34 AM   #29
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Another vote for tank tenders and sight tubes.
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Old 02-21-2015, 12:26 PM   #30
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I use a flow scan to monitor fuel use/rate and the tank tender to measure the levels in the six fuel and water tanks.
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Old 02-21-2015, 12:35 PM   #31
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They're are way more accurate solutions out such as Maretrons. No need for those big pulse dampeners either.
Although my 32' Halvorsen has a FloScan, it's not the easiest thing to calibrate...no matter what anyone says. In my (new to me) boat, the addition of the multi tank "Tank Tender" is most welcome! Other than a sight tube, the "Tank Tender" is the most accurate devise out there. (Dip sticks not withstanding.) MY OA 42 has both.
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Old 02-21-2015, 12:37 PM   #32
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Question on the Flosan.....Since there is a return line, is there a way of calibrating these to somewhat accurately measure Accurate fuel usage since some is being returned to the tank?? Or is installation in the final feed line accurate?

I have mechanical float gauges on both tanks...One easy to read through a glass port in the settee foor, the other I have to pull some panels to see. Not a big deal, and they appear pretty accurate, but i am curious on the Floscan.
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Old 02-21-2015, 12:54 PM   #33
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Question on the Flosan.....Since there is a return line, is there a way of calibrating these to somewhat accurately measure Accurate fuel usage since some is being returned to the tank??
This is done automatically in the FloScan's algorithm. The hardest thing to accomplish is an accurate calibration of the "fuel used." Instructions came with the unit for the calibration procedure but do to my limited ability to comprehend instructions, I never achieved the 1% accuracy that FF speaks of. Although it sounds neat, I would never buy another one.
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Old 02-21-2015, 01:53 PM   #34
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Although my 32' Halvorsen has a FloScan, it's not the easiest thing to calibrate...no matter what anyone says. In my (new to me) boat, the addition of the multi tank "Tank Tender" is most welcome! Other than a sight tube, the "Tank Tender" is the most accurate devise out there. (Dip sticks not withstanding.) MY OA 42 has both.

Yes that's what's nice about the maretron's. They make them super simple to calibrate. Google Maretron FFM-100 Manual to get and idea
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Old 02-21-2015, 01:56 PM   #35
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Question on the Flosan.....Since there is a return line, is there a way of calibrating these to somewhat accurately measure Accurate fuel usage since some is being returned to the tank?? Or is installation in the final feed line accurate?



I have mechanical float gauges on both tanks...One easy to read through a glass port in the settee foor, the other I have to pull some panels to see. Not a big deal, and they appear pretty accurate, but i am curious on the Floscan.

Yep, the Maretrons measure both sides. Cool thing is you can set the display up to display any combination of numbers you want like return amount NMPG, etc. The Maretron flow sensors even have temp sensors in them.
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Old 02-21-2015, 02:07 PM   #36
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Yep, the Maretrons measure both sides.
Ah...I see. They have a flowmeter on the return leg as well...

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Old 02-21-2015, 03:32 PM   #37
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This is done automatically in the FloScan's algorithm. The hardest thing to accomplish is an accurate calibration of the "fuel used." Instructions came with the unit for the calibration procedure but do to my limited ability to comprehend instructions, I never achieved the 1% accuracy that FF speaks of. Although it sounds neat, I would never buy another one.
I didn't even attempt to calibrate the FloScan. Actual fuel consumption is about 70% of that displayed, so I just use mental arithmetic.






FloScan factors both fuel to engine and well as the return to tank, so there are two measuring devices for the engine.


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Old 04-21-2015, 07:24 PM   #38
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sight tubes

We bought a trawler about 9 months ago. Though she is work in progress she is functional and we have taken numerous short day and weekend trips locally learning our new boat. Her twin tanks approx. 400 gallons were filled upon us receiving the boat. I have been watching the sight glasses pretty regularly and became concerned when they didn't show the fuel usage I figure we were using knowing how many hours I had run the engine. I had checked the valves at the top and bottom more than once to ensure they were open. This weekend while in the engine room checking things over I reached over and thumped the fuel tanks. To my horror they sounded really empty still showing about 3/4 full in the sight tubes in both tanks. I shut the valves drained the sight tubes and reconnected them. turned the valves on and low and behold they show about 1/8 full each tank. I am confused how can sight gauges be that far off. Do I have a venting issue. Ideas anyone? Considering a alternate fuel monitoring system that doesn't require going to the engine room to look. But I figured the sight glasses were probably the most accurate way to go and it never hurts to take a peek in the bilge.
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Old 04-21-2015, 08:34 PM   #39
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Sight glasses are accurate. They require that both the top valve and bottom valve be open at the same time to get a reading. At times valves are installed incorrectly and it may appear to be in the open position when in fact it's closed. So, "open" the bottom valve and then open and close the top valve to see if you get a reading in one of the positions. If not, change the position of the bottom valve and repeat the top valve routine. You should get a reading. If not, you probably have a clog in one of the valves. The sight glasses do not depend on a vent to operate. Good luck.
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Old 04-21-2015, 08:48 PM   #40
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I figured the sight glasses were probably the most accurate way to go and it never hurts to take a peek in the bilge.
They are. So as Hmason suggests, you have some sort of problem with the valves on the sight tubes or you are positioning them incorrectly.

They should be closed at all times unless you are actually taking a reading. This is to prevent a fuel spill into the bilge of your boat if a tube cracks, splits, or breaks and having that fuel pumped overboard by the bilge pump(s) and netting you a big fine if the spill is traced back to you.

When you want to know how much fuel is in a tank, open the valves at each end of the tube. get your reading, and then close the valves again. The fuel level in the sight tubes will not change again until you open the valves again for another reading.
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