Hi Group,
As I dig into my new boat, the question of how to measure fuel volume comes up. After climbing into the port cockpit locker and measure length and width I found the height concealed by the plywood framing surrounding the tank fixing it in place. It seems the depth may not be uniform so I'm not sure how to calibrate a fuel dipstick. does anybody know how to correlate inches of fuel to volume on our boats? I'm an english major BTW..
1 cu inch = .004329 gallons. I'm assuming you know how to calculate the volume in cubic inches, L"xW"xH", where height is the dipstick mark in inches from the bottom of the tank. It does not matter if the tank is tilted as long as the dipstick measurement is made near the center of the length dimension. You can prove this to yourself empirically using a clear Tupperware container filled with water. Make a mark in the center then tilt the container. The depth does not change. Pete
But Pete, what if the depth of the tank is not uniform? In other words what if the tank is 12 inches deep at the Stern and 16 inches deep forward, in other words it's not a cube.
Ah grasshopper, you learned nothing from the Tupperware lesson in my last post. Because of gravity the surface of the fuel in the tank is level. That represents the length and width of the cube. The tank is a tilted cube and measuring the depth midway along the length gives you the mean depth or height as if the tank was 14" on each side instead of 12" and 16".
(http://i1121.photobucket.com/albums/l505/banjoband/tanklevel.png)
Pete
Intern, The next trip to the boat I will get the fuel log then post the information. Allen
On Journey, I waited till the tank was empty,then added 5 gals at a time and marked the dip stick as it went up. Hope to GAWD I never lose that stick!
What's so complicated about gallons in tank = L"xW"x Dipstick" x .004329? LxWx.004329 is a constant. So now you only need to multiply two numbers to determine what's in the tank. Pete
Our dip stick hole (tank filler neck) is in the front of the tank, at the lowest part of the tank. So the calcs wouldn't work unless you did an integration of the volume as it is an irregular volume. (no constant for the lower part of the tank). My 5 gal method proved this as the marks for the lower volumes were farther apart than the ones in the cubic area near the top of the tank.
Yes, if you have the same 4" of slope forward and aft, the marks on first 4" of you dipstick will be further apart/gallon. Once the depth at the front of the tank gets to 4" you can accurately calculate the amount of fuel in the tank by subtracting 2" from the dipstick reading and multiplying. A backup position incase you calibrated stick ever goes missing.
I didn't think this was important because I always believed that was ill-advised to run a diesel tank down that low. At 2" on the dipstick you are probably looking at maybe a 3 gallon reserve and sediment. Some wave action and your sucking air into the lift pump.
I figured the original 50 gallon tank to be 24" x 32"? Let me know and provide the slope and I'll generate an app that will calculate your fuel in gallons.
Pete
Here is an Excel Spreadsheet that will calculate the volume of any rectangular fuel tank in gallons with a known slope front to back based on a dipstick measurement made at the deep end of the tank.
(http://i1121.photobucket.com/albums/l505/banjoband/tankcalc.png)
I tested this with an actual tank using water and its accurate. It calculates the volume of the right angle wedge when the dipstick measurement is below the slope of the tank. Note the second order expression (square) for you Math types. No integration needed. Simple geometry.
If I can't attach the actual file (out of space on the site) there is enough info here to type it in if you have a few minutes and if you know Excel.
Sorry about the typo here is the correct excel equation for cut and paste
= IF(B4<B8,(0.0021645*(B4^2)*B7*B6)/B8,0.004329*B7*B6*(B4-(B8/2)))
Pete
As promised here's the IPhone app for calculating fuel tank capacity and remaining fuel for any size of tilted rectangular tank using a dipstick calibrated in inches and measured at the deep end.
(http://i1121.photobucket.com/albums/l505/banjoband/tankapp.png)
You need to download the free spreadsheet app at the Appstore from Luminant Software. The format for the equation changes a little to this: = IF("B1<B7";(0.0021645*(B1^2)*B4*B5)/B7;0.004329*B4*B5*(B1-(B7/2)))
Pete
OMG I love this group! really appreciate the enthusiasm for all my foolish questions. I'm with Pete on not wanting to wait till the tank is low to dump fuel in and measure-seems like 90% of diesel engine issues are dirty fuel related and that's just daring the pump to suck up sediment. Pete, I can't measure the slope because the tank is framed in with timbers supporting the sides and holding it in place. Am I correct in assuming you have measured the slope and its 4"? Or is that just theoretical for the sake of demonstration?
Pete: You really went above and beyond the call of duty on this one. What am puzzled about is it seems like you guys must be configured differently than we are. We have a fuel gage that is supposed to be visible through a round clear window in the cockpit floor. While I can't read it through the window because it is all scratched up, I can read it directly from inside the starboard locker. Are you guys just checking the gage accuracy by a dipstick through the fill port, or do you not have a gage? In out installation, snaking a dipstick down the fill port through the hose and into the tank seems like accuracy would be suspect, unless I could calibrate it, not because the math isn't right, but because I wouldn't know how deep it was, or where in the tank it ended up.
I'm going to assume that 50 gallon steel tanks that Pearson installed have all rusted and had to be cut-up and removed. In its place owners have had to install smaller tanks capable of fitting though the sail locker opening. My 365 has a 30 gallon plastic tank with a fuel gauge sender. My plan is to turn the sender unit so the float is in the deep end. Then I will calibrate the gauge reading in inches. From there I can use the dipstick app to convert that to actual gallons.
I also think that many Pearsons have panels in the sail lockers that seal the engine compartment off. My Pearson has no such paneling at the moment. My problem with my current install is that I cannot carry enough fuel.
Pete
I have original tank, had it inspected about 6 months ago thinking from all that others have gone through that I would need to replace.
No rust, no leaks, no sludge, no algae...
Inspector said probably has always been kept full & stored good fuel????
I know my boat used to be in Florida, then in San Diego.
So it's not a location advantage.... maybe all the PO's left her in the dock?
That's what I thought until I took the tank out. Had a previous owner painted the tank I would have been even more convinced I was OK.
If you look at this picture:
http://s1261.photobucket.com/user/barrylab1/media/Relentless/Fuel%20Tank%20R%20R/Tank%20Removal/IMG_0070.jpg.html?sort=3&o=3 (http://s1261.photobucket.com/user/barrylab1/media/Relentless/Fuel%20Tank%20R%20R/Tank%20Removal/IMG_0070.jpg.html?sort=3&o=3)
you can see the corners had rust much worse than the others. The tank sat on plywood which held moisture, and accelerated the rusting process. I decided to replace it with an Aluminum replica, and when I brought the old tank to the fabricator, it began to leak the few ounces of diesel left in the tank. It was a disaster waiting to happen.
Thanks for posting those pictures of the original steel tank. I'm curious how you got it out in one piece. I did not think that was possible. Do you have the outside dimensions from the fabricator ?
It's got a mostly a flat bottom with a radius at the deep end that is somewhat insignificant in calculating volume. So the calculations for volume should work well. But the filler and dipstick opening is several inches up from the deep end.
Pete
I had to remove the engine and have it rebuilt. While it was out, I pumped the tank into a 55 gal drum, detached the connections and it came out over the plywood box without too much swearing.
I had a new tank built to the dimensions Dale gave me in a .dxf file, and it was an exact replica.
I had it built out of 0.125" 5052 marine grade aluminum, then painted it with zinc chromate primer and an epoxy two part over that.
I then replaced the plywood under the tank with acetal and machined some acetal standoffs for the staps I'm holding it down with (stainless).
I tried posting the .dxf, but this site doesn't like attachments so here's the link to the photos including a screen shot of the .dxf
http://s1261.photobucket.com/user/barrylab1/library/Relentless/Fuel%20Tank%20R%20R/Tank%20Install?sort=3&page=1 (http://s1261.photobucket.com/user/barrylab1/library/Relentless/Fuel%20Tank%20R%20R/Tank%20Install?sort=3&page=1)
Thanks for the drawing Barry! I was planning to remove the eng and change the tank in New Zealand this year, so having the drawing really helps to shop out a bid before I rip it out and lug it around for a template.
Can I ask how much you paid for fabrication as a reality check on how much I should shell out?
Cheers!
Wayne
Thank Dale (i.e. Maruska).
He put it together back when he had time to do these things. It sure came in handy for me.
Unfortunately I live near Boston, so everything is outrageous. I paid $620.00 to have it built to my specs. I've heard others say they had it done for $400.00, but that was in Texas. Be careful with the fittings. I tried anti-seize materials, but the brass to aluminum junction at the tank kept leaking air. I switched to a Nylon fitting there, and it stopped leaking. I had to ground the fuel solenoid so the rest of the fuel system wouldn't need to rely on the engine ground, but it's working well now.
I got around to measuring my tank. And using the dipstick calculator, turns out its only 20 gallons. I can't go anywhere on that. I measured the sail locker opening it appears I might be able to fit something in the range of 25 x 30 x 13 through that opening. That would get me up to around 42 gallons.
Anybody swapped out their tank with the motor in place? Would like to hear what you were able to get in there.
Thanks, Pete
Pete,
I replaced my tank with the engine in place, but I removed the nav station and the bulkhead separating the nav area from cockpit locker. I brought the tank fwd and out the companion way hatch. Even if you could get the tank out of the locker (which you can't), you might not be able to get it up and past the fore and aft stringer that runs from the rudder post support to just fwd of the engine (one on each side). I had to cut mine away and replace it once new tank is installed. If you boat is one of the few with a quarter berth, you can remove it, then pull the tank fwd around the engine.
http://s1278.photobucket.com/user/scherzoja/media/New%20fuel%20tank/P5109331_zpsqjaoor1d.jpg.html
http://s1278.photobucket.com/user/scherzoja/media/Quarter%20Berth%20and%20Nav%20desk%20rebuild/3_zpsttk7dgbk.jpg.html
Good luck Pete.
For those of you who are considering replacing tank with one of same size, you might want to consider shortening to 25" and widening to 29". This maintains the ~50 gallons, but gives you more room between tank and engine, enough to get you head between the two and it makes work on that part of the engine much easier. Just be sure you can get that new dimension tank in place (between the cockpit supports (those glassed 2x4 posts at fwd end of cockpit.
I replaced my fuel tank in 09 via engine removal used mizzen and main halyards set the engine on the gallie sole. I had the new tank made by Florida Marine Tanks (305-620-9030) They made the original tank. The main difference the new tank is aluminum old was steel . I think the old steel tanks outlasted the aluminum ones. So I had the new tank made twice as thick as standard with no fuel gauge sending unit or port. Total Invoice was 529.00. Allen
Just replaced our tank in New Zealand. I removed the engine as I wanted to do a minor overhaul to it anyways, then brought the tank out the companion way. Replaced with a .125 inch aluminum tank built at the Riverside Drive marina in Whangarei. We used the drawing that is posted up on this thread and it was totally accurate. Cost was ~&400 USD.
You can see pictures of the removal, including the cabinet cutting required on Dana's most excellent blog: http://www.galleywenchtales.com/2016/02/heave-ho-out-she-goes.html