I did a bit of searching in hopes that someone might have posted a reference guide for measuring the fuel level in the W32 fuel tanks. But, alas, I came up empty handed. Of course, I could just start with an empty tank and add fuel 5 gallons at a time,marking a stick as I went along. But that would mean completely emptying one of my tanks (which I would prefer not to do) and I would still only have a very rough estimate in 5 gallon increments. So I decided to come up with a table by means of mathematical calculations. The chart assumes the standard ~ 35 gallon tanks, as shown in Bud's Service Manual...
http://www.westsailparts.com/ServiceManual/index.php?chapter=G#G-01
(If you'd like to use my calculations, but aren't interest in how they were derived, simply jump to the end of this post.)
The challenge to this method, of course, is that the W32 tanks are such weird shapes. While this makes better use of the available space, it greatly complicates the calculations.
The basic formula was derived from the method for calculating the volume of a trapezoid tank...
volume = L * (b1 + (b2 - b1) * h1 / h + b1) * h1 / 2
There are two factors that complicate this simple method.
1) The two ends are different shapes.
2) The wall facing the hull is completely skewed.
In fact, the shape isn't really a trapezoid at all, but the formula works if you make two calculations, one volume based on the shape the forward wall and another volume based on the shape of the aft end wall, and then average the two volumes. To allow for the skewed outer wall, I made the calculations as though each tank was comprised of two individual tanks, splitting them horizontally where the hull-side wall changes dimensions at the forward end of the the tank. I'm actually not sure if I needed to do this, but it was easier for me to visualize the results in my head. (My college days of math and science are way too far behind me.)
Since I built an automated PHP routine to perform all the calculations inside of a "loop", it made little difference how many increments were used. As such, the volumes where calculated for every inch in height. The loop could just as easily have been repeated for every millimeter in height, but that would have been really anal retentive, wouldn't it? I simply wanted something that gave me a gauge to account for the odd tank shape, without the need to manually add and mark the measuring stick at 5 gal (or even 1 gal) increments.
Once I had the volume calculations in cubic inches, it was a simple matter to convert from from cubic inches to gallons by mutilplying Volume times the constant 0.0043290. In making the calculations, I allowed for a 1/8 inch of wall thickness and also chose to disregard the first inch of fuel in the bottom of the tank, because even if you could suck the tank that low, why would you want to? (If you chose to include the first inch, simply add 0.8 gal to all displayed values.
The resulting chart should give a quick and dirty method to get current fuel levels using a simple dowel, marked in inches. At one point, one of tanks had a sight gauge, but it was removed for some reason. If your tank(s) do have a sight gauge, it should be a really simple matter to use these calculations to make a reference chart behind the gauge.
I'm posting this in hopes that others find it helpful. I know I would have preferred to find the calculations ready-to-use. I no longer use my math skills as I once did. So if anyone finds discrepancy in the calculations, please let me know.
Jack Webb, aboard s/v Drifter
PS: If anyone has actually done the manual measurement using 5 gallon cans, I'd love to know how your calculations compare with mine. And if anyone else is anal enough to want to see the actual calculations made, inch by inch, let me know and I'll be happy to post them.
