Fuel Gauge, slight tube or leave it be

In working towards understanding the fuel delivery system I'd like to get a measure on owners that have either added a fuel gauge or sight tube. The boat originally came with dips. Now one of the dip holes are being used for the diesel furnace. So I have to pull the carpet, open the deck hatch and than I have access to the only dip available (one tank). Has anyone added a fuel gauge or sight tube? If so how do you like the new addition? I am thinking of adding two fuel gauges, but maybe it's over kill for the boating we do right now. But I am feeling lazy and think this might be a nice little addition to the vessel.

Fuel guage

When I bought my current boat some 2 years ago. It had dips and sight glass's.
Sadly bending into the engine bilges to look at the sight glass is arthritically difficult at times! The dip is not on the centerline, but can be used after pulling some access hatches etc. However the tank is double bottomed (1600usgall) to the hull shape which has just necessitated the taking of the hull lines and excel spreadsheet to calc the fuel for every inch of depth. (sadly the original sounding chart had disappeared over the years).

However I have just purchased a Cruz pro programmable fuel gauge along with sender unit and will be fitting that when I get back to the boat in April.
This cruz pro and the floscan's will be my daily information . I will back this up with my sight glass, every 50 hours of running etc.

Can never have enough information!!

Currently cruising in the Caribbean.

Martin

I have both sight tubes and a fuel gage.
One gage, the swing arm type in the starboard tank. Port tank doesn't have one but the tanks have a leveling line between them(1/4 ID).
I find the gage extremely accurate. I can use it to predict how much fuel I will be able to take on within about 10%.
I never look at the sight tubes because that requires crawling into the bilge.
I can also use a dipstick on the port tank and that always agrees with the gage.

Martin J said:

However I have just purchased a Cruz pro programmable fuel gauge along with sender unit and will be fitting that when I get back to the boat in April.

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Your review of the CruzPro gauge will be welcome; I'm considering switching displays, too (and as I understand it, their display should work with our current senders).

-Chris

Before I spent money on fuel gauges....I would go sight glass and a flow meter system such as fuel scan.

While there are accurate fuel gauges, the most common fuel gauges are the most unreliable thing on a boat most often, other than the skipper of course.

Every guy I bring fuel to all summer says either...."the gauge says half full" or I couldn't have used that much yesterday after I filled it". In the end I know who is half full...

Tank Tender

Over the years and 9 different boats, I've had just about all of the tank measuring devises there are. FloScans, Tank Watch, Solo, etc. The best (fool proof) gauge I've ever had (and have today ) is the Tank Tender. No electric or floats...just some 1/4 in plastic tubing & barometric pressure. (The barometric pressure is free!)

The Tank Tender - by Hart Systems, Inc.

A Flow Scan ,,would also be my first choice.

Once its dialed in it is within 1% or 2% and most skippers wont go that far down to keep the fuel cool.

It could easily pay for it self if the boat is cruised.

Floscan Instrument Co. Inc.

www.floscan.com/

FF said:

A Flow Scan ,,would also be my first choice.

Once its dialed in it is within 1% or 2% and most skippers wont go that far down to keep the fuel cool.

It could easily pay for it self if the boat is cruised.

Floscan Instrument Co. Inc.

www.floscan.com/

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They're are way more accurate solutions out such as Maretrons. No need for those big pulse dampeners either.

Check out "Fuel tank filling and gauge" thread in the Kadey Krogen section. I posted photos of our existing sight tube setup.

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.

Bshillam-- The new fuel tank the PO had installed the year before we bought the boat has four saddle tanks and a day tank. Each saddle tank has a sight tube. The day tank has a standard electric sensor fuel gauge with the display on the helm consol. The entire system operates by gravity; the only pumps are the lift pumps on the engines.

It's a terrific system.

Our sight tubes have a shut-off valve at the bottom of each tube. They really should have valves at the tops and bottoms.

Marin said:

Bshillam-- The new fuel tank the PO had installed the year before we bought the boat has four saddle tanks and a day tank. Each saddle tank has a sight tube. The day tank has a standard electric sensor fuel gauge with the display on the helm consol. The entire system operates by gravity; the only pumps are the lift pumps on the engines.

It's a terrific system.

Our sight tubes have a shut-off valve at the bottom of each tube. They really should have valves at the tops and bottoms.

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Good setup Marin. Sight tubes can be enhanced by gallons/liters markings.

psneeld said:

Before I spent money on fuel gauges....I would go sight glass and a flow meter system such as fuel scan.

While there are accurate fuel gauges, the most common fuel gauges are the most unreliable thing on a boat most often, other than the skipper of course.

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I think that's the kind (unreliable) I have.

In our case, sight tubes wouldn't be easy to install, and then also not easy to actually check.

Actually, in the grand scheme of things, our existing (original) analog gauges are close enough... when they're reading anything at all... especially since the redundancy acts like a self-check.

If one says a half and the other says empty (sometimes happens, temporarily), I can usually figure that out. If one says a half and other say a quarter, not to worry, add diesel. Usually adding the same amount to each tank brings 'em up to roughly the same. I think I have a float tube in the starboard sensor that sometimes sticks... sometimes forgets to float...

But since we're not often off-shore, and log everything reasonably closely... it's been easy enough to keep track.

But if I had those nifty digital gauges and knew to the gallon how much we have on board (assuming the sensor thing can be managed), that'd be one more nifty digital thing I could stare at... convince myself how much better accuracy I'd bought...



-Chris

Our boat has two 300-gallon fuel tanks for a total of 600 gallons. Like most of the boats on this forum, our boat is slow....and we average about six gallons per hour when traveling from point-to-point. That equates to about 100 hours of fuel when tanks start full.

We, like most of the boats on this forum, travel about 150 hours per year. So we must fuel about every nine months or so.

We don't need fuel gauges! Sight tubes work fine. We have ball valves at the top and bottom of the sight tubes. I open the valves when we take on fuel, about every eight or nine months.

Should our boat usage dramatically increase, We'll consider a fuel measuring system. Until then, we just occasionally glance at the fuel levels when I'm checking engine oil/coolent levels, etc, in the engine room. Keep it simple!

Ditto !!
Except I have 500 gallons in four tanks and Stewart Warner electric fuel gauges, which have proven to be surprisingly accurate. The tanks are all at the same level and are connected with a crossover system, so they self level. It's easy to compare the gauges and the indications are nearly always identical. (When they aren't the same, it's because I closed the crossover while refueling and forgot to reopen them.) I usually fill up when the gauges reach 1/2 tank which is in the neighborhood of 240 - 260 gallons

We have no idea how accurate the electric fuel gauge on our 60 gallon day tank is. But it doesn't really need to be all that accurate. When it gets down around a quarter full we refill it via gravity from the oposing pair of saddle tanks we're using at the time.

The sight tubes on the forward opposing pair of saddle tanks have gallon markings on the tanks behind the tubes. So we can tell pretty easily how much fuel we have on board. Like Ray, we've found that exact accuracy in fuel quanties on boats like ours is not important. As long as we know about how much we have, we can determine when and if we need more.

To the OP:
If you have mirror image identical shaped/size tanks with an OPEN crossover valve, and the boat is on a level keel, you only need to measure one tank as the the other tank will equalize level. One dip stick would be close enough. Surely as close as any remote gauge other than a sightglass. The bonus is no additional work needed.
Now if your boat has a list, different shaped tanks or the crossover valve is closed, my favorite is the dear old tried and true sight glass.

My boat came with a Tank Tender for both fuel tanks and the water tank.

It's very accurate. When I fill the fuel tanks I'm always within 2 to 6 gallons of my estimate based on the Tank Tender readings. Normally these are 200-250 gallon fills.

The simple solution might be to

1. Measure the tank and find its capacity.Subtract 25% for safety

2 . Fill the tank go for a 10 hour cruise.

3. Fill the tank again .

Note run times in your log , and leave a note ,

Engine hour meter reading xxx, (whatever) its time to fuel or switch tanks.

Pencils can be found at low cost everywhere.

HiDHo said:

Check out "Fuel tank filling and gauge" thread in the Kadey Krogen section. I posted photos of our existing sight tube setup.

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Sight tubes are never wrong, unless you have the top or bottom valve closed.
Don't all why I know.

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 .

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.

Marin said:

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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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

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.

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.

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.

Steve said:

I guess spring loaded, turn to open, close automatically valves may available.

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"Push" to open valves have been around for a long time. The photo below is 7 years old.

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.

Another vote for tank tenders and sight tubes.

markpierce said:

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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