Originally Posted by psneeld
Can always burn it down low, pump out till sucking air...
Mark that on sight tube (or add fuel till it becomes visible and you know that is reserve).
Then add and mark accordingly.
You can either stop at the top of the sight gauges or go till venting (oil pads under vents of course.
That way you are sure, not "estimating".
You may have had full tanks and the sight gauges were blocked or "shut off" ( hopefully not insulting your intelligence but there are some unusual or broken valves out there).
+1 This is what we did on NWD. We did not have any calibrated markings for our sight gauges. After doing similar work on both tanks, we left one EMPTY. We had discovered the tanks are not symmetrical from bottom to top. We then filled it up until it started to show on the sight gauge, so I know how many gallons to the bottom of the sight gauge, which is just above the level of valve for the fuel supply. Then filled it 10 gallons at a time (we did this when the fuel dock was slow, believe me!), marking a piece of tape as we went. This is now our template to create permanent marks for our sight gauge guards, calibrated to the nearest 10 gallons (on 200 gallon tanks.) I can quickly visually estimate my gallons on board to the nearest 5 gallons, and with a tape measure reasonably measure my fuel use within a gallon or so if I really wanted to, if I'm sitting in calm conditions....for most of my sight gauges its between 1" and 1 1/8" per 10 gallons....
After we did this, once we were in a position to run the other tank down to nothing we did the same thing to mark it... It took us a while simply because I didn't want to have one tank completely full and the other completely empty at the same time... We actually went a little over 1/2 tank at a time on each side.... then the rest of the way once we'd done that.
As to comments/pictures of builders tags on fuel tanks... ha! I don't think all TT's got them. I uncovered almost every surface of my tanks during the work I did on them, and while I believe I was seeing the original surfaces (as once I removed the sound baffling I found a page of a newspaper laying on the port side tank from the year she was built!) I found no builder plates at all....My tanks appeared to have been built by a craftsman who bent and welded the tank to fit the space it needed to fit - the tanks are similar but not exactly the same.