Fuel tank volume calculations

What calculation Zappi?

Okay, here's the easy way for you to do this.

At the fuel dock, syphon the remaining fuel out of the tank until the engine

quits. Dip the tank, measure up two inches and mark this zero.

Fill the tank (from the pump) stopping, dipping and marking the stick in

whatever increments your little heart desires, 5 gallons, 10, whatever.

OR, keep the tank topped up, then you'll know you always have lots of fuel,

minimize condensation problems and avoid sediment in your fuel line while

enjoying the benefit of a well balanced boat (providing it was designed

properly).

-Tom

 

"avoid sediment in your fuel line" - the feed should come out of the lowest point of the tank anyway.

 

Should it? As you wish 775.

-Tom

 

It absolutely is not as I wish. It is the way it should be done. Do you want **** lurking in there waiting for the first rough weather to clog your feed or filter, or do you just wanna' get it out of there and into a filter to be discarded? A tapped-for-draining sump is a distant second best option.

 

I thought I posted it but apparently I was thinking of cheerleaders and didn't. Empty the tank and then mark it as you fill it. If you try and calculate it by the shape of the tank it will probably be off as the boat and tank won't set level in the water. A stick is only going to give you a crude idea anyway, and if the boat is jumping around or the stick is wet, you won't be able to tell much. You need to put a gauge on it if it's important.

 

That's ("It would be easier for you to go inside and plug it into a program than to simply have already calculated "four inches is twenty gallons, five is twenty seven, six is 36, or whatever"? You don't even need to do that - just fill it and mark the stick you'll use every five gallons as you put it in. I'd do the calculation for you but I couldn't get the thumbnail to come up.") a good idea!

 

If that simple little equation I posted is too difficult, perhaps things are worse than I thought Its a no brainer to use the equation and mark a stick off for fuel level. Same thing can be used to calibrate a fuel gage.

Edited to add that I just replaced a shop made FG tank with a Moeller plastic one because of ethanol issues. The tank was not exactly accurate to the drawing dimensions and was about 22 gallons effective instead of the stated 25 gallons. I also did not allow for the wall thickness in the formula given for which I would allow 1/4" for each wall.

 

Tom, it's not so simple. I asked you how you arrived at the constants? Is that formula out a tankerman's book or what? I'm a little dense here, I 'spose. I just would like to know that formula. Like all math, plugging it in doesn't teach us - we have to understand the "why". Sorry, can you help me out? I help my kids but it has been 30+ years since I had math and I have no idea!

 

Tom, you and I learned this stuff before pocket calculators and it wasn't particularly hard. These kids have a world wide web and are climbing mountains over this. I'm fairly sure this is pre-high school math folks. In collage, the first pocket calculators appeared for me, but we weren't permitted to use them in class.

This is can be handled a few different ways, the easiest is the trapezoidal rule, which is 1/2 the sum of the parallel sides, times the altitude, times the length.

You could also use the trapezum rule which is treating it like an irregular quadrilateral, where the end plane is divided into two triangles, then combine the area of these, again multiplying by it's length.

If you really wanted to get anal about it, you could use Simpson's or Durand's Rule also.

 

Okay, Smartasses. I can explain volume = L * (b1 + (b2 - b1) * h1 / h + b1) * h1 / 2 the formula I posted. Can you please explain where the constants came from in this Gallons in tank = h(885 + 11.44h)/231
h = height of gas in tank in inches formula? That's all I'm asking. Do your numbers derive from the formula I posted? I couldn't see the drawing for some reason and I have no idea where the numbers 855, 11.4, and 231 come from. Just like in school - SHOW YOUR WORK. You've had sufficient time to go look it up! it's been two pages!
A problem with this forum is most people are much more in tune with impressing themselves than helping. I might as well be trying to get Wiki answers from the stupid global economics thread.

 

Oh my God people, get a grip.

This is simple math or even simplier, fill the frig'en tank.

22 gallons, 26 gallons, 85 gallons, "Did you check my calc?"

It's about 11 cubic feet (if we must work in imperial) and that's about

70 imperial gallons, maybe 75 US, how many bushels???

If you're trying to figure out your tank volume then take some

responsibility and figure it out. It's your *** on the line if you run out of

fuel. Don't ask, or even trust, somebody else to do it for you.

This thread should be renamed: How Stupid Can We Get

-Tom

 

Tom, it's purely academic for me. Sorry, maybe 'cause I have four kids, I treat everything as an opportunity to learn or teach and I just got a little pissed at the condescension of some that don't know the math any better than I. Why is it stupid? I'm calling some people out. If everybody can talk about how much better they are than everyone else, they can, at least, back it up with... something! "Harumph...slide rule, these kids, bla, bla, bla." Why, one might ask, would a man with so much to offer...offer this? Does every thread here have to devolve to this upmanship?

 

I agree with Tom.

Except Tom, YOU should get the grip Gallons ? or is it Gallings. Haven't we decided to use the metric system so everyone can get their math right ?
Right


Calculating the volumes of different shapes is very easy. While we can give advice here, the onus is still on the person who asked the question to do a bit of research instead of expecting a spoon feed. I'd hate to be taught like a kid, except if she's good looking with nice ****.
Sorry, that slipped out

In grade 2 we learned that you devide the shape, in this case it's a rectangle and a triangle - the rectangle which is calculated by multiplying Length, Width and Height, where Height is the depth of the fuel.

The triangle is calculated Side Angle Side (you can search it in Wikipedia yourself good grief, basic trig) where the Angle is fixed and again the Side and Side is the depth of the fuel. Since the angle is small the extra length in the slanted side is negligible and the two sides can be assumed the same, but you can also measure the length of it and calculate to the nearest drop.

Once you have to two volumes they simply gets added and you know the amount of fuel in the tank.


Logic tells me no one is going to sit on the water with a calculator and calculate the fuel level. If the tank is transparent ie PE, then you can make marks on the side to see the level, if it's ie SS then you may have a stick you push in it to measure the level, or you may use an electical fuel level indicater, the latter is the obvious choice and it is convenient.

In all cases you want to calibrate the measurements. Simplest is probably to add a known abount of fuel and mark the level, add the next known amount of fuel and mark the level and so on. Do not exceed full You don't even need a calculator to follow this method, you just have to do it.

You may also want to impliment a bit of a reserve for emergencies. Nothing is as bad as trying to add fuel to the empty tank in bad weather.

 

OK, sorry that I don't sit here at the computer all the time. While away, apparently some felt I was being "superior" or some such s**t. Actually, I was just giving the opportunity to do some dog work for themselves.

It's just grade school math, not rocket science. The "constants" are not constants at all, just the results of calculation based on the particular tank. Looking at the end of the tank, there is a rectangular section 15" x 18" and a right triangular section 7" x 18" and the length is 59". The h in this case is 18" and the volume is (15x18 + 7x18/2)x59 = 19635 in^3. Divide that by the cubic inches in a gallon and the answer is 85 gallons.

Of course, we don't know the width at the top of the triangular section for partial full tank so we have to calculate it as another variable. Here comes a little trigonometry. The ratio of height to base of the end triangle is the same at all heights or: (22-15)/18 = 0.388. Therefore the area of the triangular section at any height is 0.389h x h/2. That is where the second h comes in.

So the derived formula for the volume of the tank is:
(15h +0.389h/2)x59
or simplified a bit to 885h + 11.44h^2 or h(885 + 11.44h)
To get gallons, divide by 231 cubic inches per gallon.

If the actual dimensions and thickness of the tank walls is known, subtract that from the dimensions I used. This kind of piecemeal division of any tank with flat sides will allow calculating the tankage.

I am very sorry if this sounds (fill in what ever you like here) but I thought the method based on the simpler math would be easier than those other formulas to understand. On the other hand, this is not a classroom and Mark is not the teacher. I don't feel any particular obligation to "show my work" but did so anyway.

For an existing tank, the method of pouring known amounts in the tank and calibrating a stick or gage works well and most have used that but for a new design, it's nice to know the available volume of a space ahead of time.

Edited to add: Yes, I can guess who gave me a negative rep.

 

I'm not asking to be spoon fed. I asked a simple question because I couldn't see the picture. Thank -you for showing your work.