How Do You Dip Your Tanks?

[Dockhead]

Originally Posted by a64pilot

The outboard squeeze bulb will work fine, but unless you have an actual low spot in your tank, little puddles of water will sit in different places on the flat bottom of a tank as there will be several low spots, if you have a flat bottom tank, that is when you want a pump and filter so you can move the tube all over the bottom and suction up any little puddles there might be.
I've never, ever gotten anything in my Racors, I put the dual one on too, but have never had a clogged fuel filter in my life, I guess I'm just lucky, but I have never cruised and fueled in far away places either. I do replace my fuel fill O-ring though, I beleive often that is where water comes from.
My Brother had a boat that had ongoing water issues, I traced that down to a stupidly placed fuel tank vent, once I moved the vent, no more water.


If you have water, where is it coming from? Tanks don't "make" water, now all Diesel has some dissolved water in it, that is unavoidable, but I don't think without a large temp drop it will come out of solution?

I think most theories concerning condensation are myths, and that 99% of water in fuel tanks either comes in with a bad load of fuel, or more likely, gets past the o-ring in a flush mounted fuel filler in the deck (AKA the work of the devil), or a tank vent which is in the way of green water.

My boat is very well designed in that respect -- fuel filler is high above deck level under a cover in the side of the cabin top, vent in the cockpit.

So I have never had any water; never found a drop either in my Racors or in my tank when cleaning it.

But if you want it to stay that way, you can't ever let up on the vigilance.

[deblen]

Originally Posted by a64pilot

The outboard squeeze bulb will work fine, but unless you have an actual low spot in your tank, little puddles of water will sit in different places on the flat bottom of a tank as there will be several low spots, if you have a flat bottom tank, that is when you want a pump and filter so you can move the tube all over the bottom and suction up any little puddles there might be.
I've never, ever gotten anything in my Racors, I put the dual one on too, but have never had a clogged fuel filter in my life, I guess I'm just lucky, but I have never cruised and fueled in far away places either. I do replace my fuel fill O-ring though, I beleive often that is where water comes from.
My Brother had a boat that had ongoing water issues, I traced that down to a stupidly placed fuel tank vent, once I moved the vent, no more water.


If you have water, where is it coming from? Tanks don't "make" water, now all Diesel has some dissolved water in it, that is unavoidable, but I don't think without a large temp drop it will come out of solution?

I respectfully disagree-tanks on land & on a boat DO "make" water-from condensation-especially in cool climates.

https://www.youtube.com/watch?v=7FU1a7yDf4w

There are several more videos,etc. if you Google "water in diesel"

[a64pilot]

And yet there are other opinions
Does An Empty Tank Condensate? Photo Gallery by Compass Marine How To at pbase.com

Being a pilot and having it beat into my head from day one, I leave my tank on everything, even the lawnmower, full. I think that helps, can't hurt

[Dockhead]

Originally Posted by a64pilot

And yet there are other opinions
Does An Empty Tank Condensate? Photo Gallery by Compass Marine How To at pbase.com

Being a pilot and having it beat into my head from day one, I leave my tank on everything, even the lawnmower, full. I think that helps, can't hurt

I agree with Maine Sail. It's a myth.

My father always religiously kept his tanks full, and filled up after every single time we took the boat out

He still had water in the tank and diesel bug, which he fought with for decades.

I only fill my tank twice a year and never worry about it being empty.

Never a drop.

That doesn't prove anything, but Maine Sail's different experiments, on the other hand, do.

You can also work the problem with dew points and the amounts of water which air can carry. There's just no way for significant amounts of water to get into your tank via condensation.

[valhalla360]

Originally Posted by Dockhead

I think most theories concerning condensation are myths, and that 99% of water in fuel tanks either comes in with a bad load of fuel, or more likely, gets past the o-ring in a flush mounted fuel filler in the deck (AKA the work of the devil), or a tank vent which is in the way of green water.

.

Agreed, I ran the calculations once and if you have 100 liter airspace in a tank and the air changes over once per day. If every last bit of water condenses and enters the fuel, it will takes over 4 months to get just a cup of water.

In reality, you aren't going to condense anything close to 100% of the water in the air and with a single small vent line, you aren't going to change over 100% of the airspace as the air expands and contracts with daily temperature variations.

Also, to get condensation, you need significant temperature differences. The problem with this is most fuel tanks are separate from the hull. As a result, the air space in the tank and the air space in the bilge tend to go up and down in temperature at similar rates. Minimal temperature differences equal minimal condensation.

Even if condensation forms, a good percentage will evaporate before getting into the fuel. (if you go out into the cold, you eyeglasses will often fog up. Give them a couple minutes and the fog goes away. That's condensate evaporating.)

It's somewhat variable but I would be surprised if you picked up even 1/4 cup of water over a 4month winter layup.

Assuming you turn over your fuel on anything like a regular basis, you just aren't going to pick up significant amounts of water from condensation.

If you come back to the boat in the spring and there is a few cups/half gal of water, your time will be far better spent looking for a leak or other source of water.


Edit: This all assumes 100% humidity. Drop it to 50-70% and there is even less water available.

[deblen]

Interesting results by Maine Sail!!
I hope Maine Sail does further testing with fuel in tank.

Then how does water get in our boats tanks?
Water also accumulates in in-ground & above ground diesel & gas storage tanks-I've had experience testing them.
I will accept some "accidental" contamination happening on the way from refinery thru to end user,but this should be relatively rare & local.

Pour cold fuel in a jug on hot,humid day & you get condensation on outside of jug where the cold fuel touches.-just like an iced drink. Granted there is less volume of air inside tank,and the "touched surface" is under the fuel....

[Dockhead]

Originally Posted by valhalla360

Agreed, I ran the calculations once and if you have 100 liter airspace in a tank and the air changes over once per day. If every last bit of water condenses and enters the fuel, it will takes over 4 months to get just a cup of water.

In reality, you aren't going to condense anything close to 100% of the water in the air and with a single small vent line, you aren't going to change over 100% of the airspace as the air expands and contracts with daily temperature variations.

Also, to get condensation, you need significant temperature differences. The problem with this is most fuel tanks are separate from the hull. As a result, the air space in the tank and the air space in the bilge tend to go up and down in temperature at similar rates. Minimal temperature differences equal minimal condensation.

Even if condensation forms, a good percentage will evaporate before getting into the fuel. (if you go out into the cold, you eyeglasses will often fog up. Give them a couple minutes and the fog goes away. That's condensate evaporating.)

It's somewhat variable but I would be surprised if you picked up even 1/4 cup of water over a 4month winter layup.

Assuming you turn over your fuel on anything like a regular basis, you just aren't going to pick up significant amounts of water from condensation.

If you come back to the boat in the spring and there is a few cups/half gal of water, your time will be far better spent looking for a leak or other source of water.


Edit: This all assumes 100% humidity. Drop it to 50-70% and there is even less water available.

All correct, and it's even worse than that.

There are two factors:

1. How much air is "breathed" into the tank.

and

2. How much water can be condensed out of the air, which gets "breathed".


The answers to both questions depend on the temperature fluctuation of the tank. On a daily basis.

So how much does the temperature of your tank vary, between day and night? The greatest variations will be with tanks which are integral to the hull in a topsides area. The less communication with the topsides, the less the variation. My tank is nowhere near the topsides, and the temperature rarely varies more than one or two degrees (yes, I've measured it).

The amount of air which will "breathe" in and out even with a variation of 10C is very small. For my completely empty tank, 700 liters, it would be 31.5 grams of air which is pushed out when the tank temperature increases by 10C (and that assumes that the tank doesn't expand, which is unrealistic -- the tank might actually expand enough to cancel out the breathing, but let's take the worst case).

So how much water can 31.5 grams of air hold at say 20C? The answer is 15 g per kg of air, which means -- 0.472 grams.

Aha, but that will not condense out when the air is cooled to 10C, because air at 10C also can hold some water, namely 7.8 g/kg. So the maximum amount of water which can condense out is 0.227 grams of water -- that is out of an entire tank of air. That's 2.8 drops.

AND, that is only if the air which is breathed in is at 100% humidity.

AND, that assumes that all the air breathed in, is at the highest temperature.

In fact, air will breathe in at night when the tank cools down, when the air is not at its maximum temperature. I think it actually could be the case, that tank breathing will be more likely to remove water from the tank, than put it in.

AND, a 10C temperature variation is more than probably any boat will ever experience. On my boat I've never seen more than 2C.



So I find it completely clear, that it is utterly impossible for a tank to accumulate significant amounts of water through condensation, and that this is a totally mythical problem. Water in the diesel tank comes from:

1. The fuel (and water can condense out of fuel just as it can condense out of air).

2. Sea water in the filler (flush with the deck fillers -- work of the devil).

3. Sea water in the vent.

Period.


The practice of keeping the tanks full all the time is actually harmful, because it means the fuel is older and sits around longer in the tank. It's much better to buy it as you use it.

[nigel1]

If you want a sample from the tank bottom, use something like this
http://www.humboldtmfg.com/manuals/H...7_man_0411.pdf
we used them on tankers to get fuel/water samples.

Barnakiels suggestion with flexible hose and finger will likely do the accomplish the same and for a lot less money.

[a64pilot]

I think lots of the water comes in the fuel, Military we had to recirculate fuel through a filter / drier and then perform an Aquaglow test, which told us the dissolved parts per million of water in the fuel, we had to continue to recirculate the fuel until the Aquaglow read below a number that I do not remember.
A desiccant filter is very easy to fit on a vent line if you think water is getting in that way, there are many made just for that, sort of like the stink filter you can put on a holding tank vent.

Once I fixed my Brothers vent, and on all boats I have owned, I have never gotten a drop of water.
Actually back in the 70's my Fathers little Cuddy cabin got water in the fuel, we never did determine where it came from, it didn't re-occur.


Sent from my iPad Pro using Cruisers Sailing Forum

[Kenomac]

We've had this discussion before. Install a custom high quality fuel polishing system for around $1500, then never worry or pay $1000 ever again.

[Dockhead]

Originally Posted by Kenomac

We've had this discussion before. Install a custom high quality fuel polishing system for around $1500, then never worry or pay $1000 ever again.

I think a fuel polishing system is a great thing, but it's only one part of the puzzle.

It doesn't clean the tank.

And it doesn't deal with what's at the very bottom of the tank, if it doesn't draw through the bottom like Jedi's and Minaret's.

I will have a fuel polishing system on my next boat (like Jedi's in the diagram above, drawing through the bottom of the tank), but I won't bother on this boat, because it wouldn't accomplish anything meaningfully more than what my dual Racors already do.

[Kenomac]

Originally Posted by Dockhead

I think a fuel polishing system is a great thing, but it's only one part of the puzzle.

It doesn't clean the tank. Yes it does, continuously each time it's turned on.

And it doesn't deal with what's at the very bottom of the tank, if it doesn't draw through the bottom like Jedi's and Minaret's. Designed properly, there should never be residue or build up on the bottom of the tank, the polishing system will continuously wash the bottom of the tank.

I will have a fuel polishing system on my next boat (like Jedi's in the diagram above, drawing through the bottom of the tank), but I won't bother on this boat, because it wouldn't accomplish anything meaningfully more than what my dual Racors already do. We have switchable Racors in addition to the fuel polishing system

Like I said: "Install a custom high quality fuel polishing system for around $1500, then never worry or pay $1000 ever again." Our system polishes 150 gallons per hour and is run 4-5 times per week or nearly every time we run the generator.

Our fuel tank couldn't be any cleaner, now going on three years since the installation.

Good God... spring for the polishing system. What's $1500 in the scheme of things?

[seabreez]

So I think about dipping the tank -- pulling up whatever is at the bottom of the tank and having a good look. I just can't quite figure out how to do it, practically.

I cannot practically dip or measure my tank as the tank is built in fiber glassed under the floor. I only have an access cover for the gauge. And I am also afraid to hit water. My next best option... I lengthen the dip tube (the pickup tube) to 1/8 inch before hitting bottom of the tank and cut the bottom end at 45 degrees. That way I am sure I will pick up any and all the water and dirt that accumulates at the bottom rear of the tank (the lowest spot).

I then added an inline canister type fuel filter, water separator that is visible at all times. It has a valve at the bottom to drain dirt or water should it accumulate. I, like you always careful to where I fuel up and I never had to drain dirt or water out. And the best thing about this is that I can check 100% of the time, not only on maintenance day. Regards, Roger.

[Cheechako]

Buy a small tubular type Plastic hand bilge pump? $15


You don't need to spend $1500 on a polisher. $25 screw on large diesel filter and a Walbro pump will do it for an oft used system.

[s/v Jedi]

Some random points (it's how my brain jumps back and forth

- ever since the beer brewer pipette has been mentioned you got the easiest method to take samples. Don't dismiss those posts thinking it needs to be a glass tube, because it has been posted over and over that a transparent vinyl hose can be used as well.

- there are old ways and new ways to doing things. For fuel pickup the old way was to keep the tube a distance above the bottom of the tank so that dirt wasn't drawn in. The obvious flaws of that plan are 1) you give dirt the chance to accumulate there and 2) you can't use the tank capacity
The new way is to attach a short piece of fuel hose to the end of the pickup tube so that it makes a 90 degree bend and shaped like a "J" picks up from right at the bottom level. Now you can use all fuel and get all dirt and water in the filter where it belongs instead of saving it in the tank