In a message dated 7/27/03 12:03:40 AM, Arild writes: << The limitation of most of these systems is that the display is an analog meter movement. I checked the website and found no indication that the technology is sufficiently advanced to give excellent accuracy. Tank Watch does use a more reliable method and with care can achieve good accuracy. >> A problem with Tank Tender type fluid measurement systems, and in fact all measurement systems that measure the fluid height in a tank is that a calibration table of fluid height vs. volume must be made to accurately estimate the amount of liquid remaining. This is no big deal if the tank is rectangular but does require a bit of calculation if the tank is cylindrical, tapered, or irregualar in shape. For tanks of unknown geometry, the best way to prepare this calibration table is to start with the tank empty, then sequentially add known amounts of fuel or water and note the reading on the gauge. The analog reading on the gauge is another problem. The 3" dial face of the gauge permits only about 10" of scale length. This permits only about 100 incremental measurement steps when seen from a normal control panel viewing distance. But then trawler owners tend to obsess over precision measurements. The gas gauge on my car has only 4 increments, and those of dubious accuracy. I havn't run out of gas in years. Larry Z

A problem with Tank Tender type fluid measurement systems, and in fact all measurement systems that measure the fluid height in a tank is that a calibration table of fluid height vs. volume must be made to accurately estimate the amount of liquid remaining. This is no big deal if the tank is rectangular but does require a bit of calculation if the tank is cylindrical, tapered, or irregualar in shape. For tanks of unknown geometry, the best way to prepare this calibration table is to start with the tank empty, then sequentially add known amounts of fuel or water and note the reading on the gauge. REPLY Quite true! Which is why a flow gage with a totalizer is often a better way to go for something critical such a fuel remaining. Scan flow and Bendix makes a very nice fuel flow instrument with gallons per hour and miles per gallons ( when combined with GPS) as well as the totalizer count. Flat horizontal tanks are harder to measure than tall vertical tanks since the same amount of liquid will result in much less vertical change in the wide flat tank than the tall narrow tank. Larry wrote: The analog reading on the gauge is another problem. The 3" dial face of the gauge permits only about 10" of scale length. This permits only about 100 incremental measurement steps when seen from a normal control panel viewing distance. But then trawler owners tend to obsess over precision measurements. The gas gauge on my car has only 4 increments, and those of dubious accuracy. I havn't run out of gas in years. REPLY While it's true about the gauges and ultra precision may be not be required, boats with multiple tanks do require a better means of determining tank content. Dave Gerr makes that point clear in his article in Professional boat Builder. He discusses the need for transferring fuel to maintain proper trim. Another article by David Blount NA in the same issue discusses some other aspects of maintaining trim. While that article deals more with the hydrodynamics of hull shape and the effect of water flow, he makes the point that over powered hulls can be adversely affected by a slight bow down trim such as caused by tankage and weight of fluids. If you have a large holding tank forward or a large water tank aft this can affect hull performance in certain conditions. Hulls that fit into the semi displacement design class are more prone to this than heavy full displacement hulls. I would guess the issue of obsessing over ultra precise measurements is not restricted to Trawler owners. The wisdom lies in knowing when to fuss over precision and when to be satisfied with approximations. < grin> --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.423 / Virus Database: 238 - Release Date: 11/25/2002