The Art of Pool Length Measurement

Hi, Anna Lea, We are so fortunate to have a School of Engineering at Southern Illinois University. I consulted with the professor who teaches surveying. He and his students will be measuring our 50 meter X 25 yard pool next month. I also asked his advice concerning measurement using a tape for those who were not so fortunate as to have free surveyors. I shared this information with Pieter Cath and these guidelines will be included in the LMSC handbook. Also, the directions on the final revision of the Pool Certification form are a bit simpler than those you listed in your message. GUIDELINES FOR POOL MEASUREMENT The 2003 USMS Rules provide that results from events conducted in pools that do not meet the minimum pool length requirement (minus 0.00M) shall not be acceptable for Record Applications or Top Ten submissions. All competition pools shall be measured in each lane. In measuring your pool, the goal is to meet the minimum length requirement. Your pool should not be shorter than 50.00 meters (164 ft, 1/2 inch) for long course; 25.00 meters (82 feet, 1/4 inch) for short course meters; and 25.00 yards (75 feet) for short course yards. Pool certification shall be reported on the USMS pool certification form. Certification data need only be filed once unless structural changes have occurred since original certification. If your pool has a moveable bulkhead, you must have an initial pool certification on file for each lane. In addition, for pools with moveable bulkheads, course measurement of the two outside lanes and a middle lane must be confirmed at the conclusion of the session (each day of the meet). HOW TO COMPLY: First check with your LMSC or the USA Swimming LSC to see if a pool certification is already on file. If so, check that the measurement was done with a steel tape or electronic distance measuring device. Fiberglass tape is not acceptable. Also check to see that each lane was measured. Electronic measurements are superior to tape measuring techniques. The services of a professional land surveyor may be your best choice. Check with the Civil Engineering department of your local university. They may be willing to do your pool measurement as a project for surveying students. Some community colleges also offer surveying classes. Each state has a State Professional Land Surveyors Association which maybe able to provide free or inexpensive services to your non-profit organization. Perhaps you have such equipment already on hand and know how to use it properly. If so, you need to be aware of the tolerance levels of your equipment over the distances required. It must be accurate to the 1/100th of a meter (1 cm). To achieve this accuracy, the markings on the tape must be to the millimeter, thousandth of a foot, or eighth of an inch. There are handheld laser devices available, priced around $500, that can measure over these distances with accuracy to the millimeter. If you must measure with a tape, use a steel tape longer than the distance to be measured. Typically, this would be a 200 ft tape for 50 meter pools and 100 ft tape for 25 yard or 25 meter pools. Be attentive to the markings of the tape. Some are marked in tenths of a foot, others in feet and inches, others in meters. Fiberglass tapes are not permitted. The tape should be supported at the same elevation every 20 ft. to prevent sag. This can be accomplished using kickboards, support poles, or threading the tape through pull-buoys. Thus for a 50 meter pool you should have at least 9 kickboards. Be sure that your tape is taut. Unsupported tape over 50 meters will require about 44 pounds of tension to eliminate sag, 30 pounds over 25 yards/meters. The tension can be determined using a tension handle attachment to the tape. Measure your pool with touchpads in place if they are generally used in competition. Have touchpads at each end of the pool if that is your usual configuration. Note on the certification form whether touchpads were in place for the measurement and how many were present per lane. Most touchpads have a thickness of 8 mm (.008 meters) but could extend out further in the pool if they are not flush with the wall. If a visual inspection indicates irregularities in the wall of the pool, one can use a waterproof vertical level of the appropriate length (80 cm minimum) to make sure the wall is vertical. If the level cannot be submerged, one can fasten a yardstick or other device to the level in order to reach the required depth. Only if the walls bow inward toward the pool would an actual measurement be necessary.

Hi, again, Anna Lea, New Rule 105.1.5 states: "Results from events conducted in pools that do not meet the minimum pool length requirement (minus 0.00M) shall not be acceptable for Record Applications or Top Ten submissions." In an earlier draft of our Guidelines for Pool Measurement, we had this wording: "Your pool should not be shorter than 49.995 meters (164 ft, 1/2 inch) for long course; 24.995 meters (82 feet, 1/4 inch) for short course meters; and 24.995 yards (74 feet, 11 7/8 inch) for short course yards." Pieter asked for the above wording, but then he changed back to the 50.00 meters, 25.00 yards in the final version of the Guidelines in an attempt to avoid confusion. Nonetheless, he agrees that the earlier wording is more precisely correct and coincides more closely to the directions on the Pool Certification form. At any rate, the following information regarding the accuracy of the tape is still in the Guidelines and should help in deciding the quality of tape to purchase: "To achieve this accuracy, the markings on the tape must be to the millimeter, thousandth of a foot, or eighth of an inch. "

I have a couple of concerns here. When measuring the pool, one has to allow for touch pads (as stated in the instructions). If you never plan to have touch pads, there is no problem. If you are going to have touch pads, then you either take your measurement with the touch pads in, or you allow for them in your calculation. For long course pools, sometimes touch pads are put in both ends of the pool. ( I would also suggest that this is also important with pools that have bulkheads). If you are fortunate enough to have supervised students from an engineering class, they may forget to take that into consideration. There are handheld laser devices available, priced around $500, that can measure over these distances with accuracy to the millimeter. Mary, would you let us know where these devices can be purchased, in the past we have seen laser measuring devices with this accuracy costing more than $5,000. Electonic pricing is always coming down, so devices this accurate may be available. If they are, I think we would like to purchase one. If any measurement is very close, ie about 50.03 meters, and the measurement is made with a metal tape, remember that the tape was probabily calibrated to a measurement made at 20 Deg C. If the temperature is warmer (or cooler), you may have to calculate the length after including the co-efficient of expansion. michael

Hello, Michael, We plan to measure our pool with touchpads in place at both ends of the 50 meter pool because that is the configuration that we generally use for long course. If we find the pool is too short, we will measure with touchpads at just one end and discontinue our practice of using touchpads at both ends. World records have been set at our facility and the previous measurements seem to have given us sufficient space for two 8 mm touchpads. We'll see. While I don't want to promote any particular brand of laser apparatus, an Internet search produced this Canadian website for a LEICA Disto Lite Laser Distance Measurer which is said to be accurate to the millimeter at the distances we require: www.deakin.com/product.cfm Aprox. US Price:   $449.08 This product was also shown at the following US website, but no price was listed. www.forestry-suppliers.com/.../View_Catalog_Page.asp With regard to the coefficient of expansion, an earlier draft of the Guidelines for Pool Measurement included the following information. "Steel tapes are standardized at 68 degrees Fahrenheit. The coefficient of expansion on most steel tapes is .0000065 ft per ft and average 0.01ft every 15 degrees over a 100 ft distance. If your water/air temperature were around 83 degrees, you would experience a stretch of your tape of 0.01 ft using a 100 ft tape or 0.02 ft with a 200 ft tape. Thus your pool may appear to be shorter than it really is. Record the measurement without correction for temperature. Also record the temperature. Only if your pool measurement comes up short would the temperature factor need to be considered." We felt this too technical to include in the final version, since the stretch of the tape at higher than the 68 degree standard would not have much impact. The greatest source of measurement error with a tape is sag. Hope this is helpful.

Mary, You state that the tape must have an accuracy of 1/100th of a meter (0.010m) over the distance measured (I'm assuming 50 meters). The pool certification form that I quoted stated that the tape's accuracy must be 0.005m. That's twice the accuracy of 0.010m. Did your figure, 0.010m, come from Pieter Cath? The reason I ask is that usually the price of the measuring device goes up as the guaranteed level of accuracy goes up. In our case, we're going to have to purchase a tape because one of our pools has a movable bulkhead.

I can't tell you the *pride* I feel reading this thread!

Hi, Michael, I think the tolerance has to be less than 0.5mm I believe the tolerance required is less than 5 mm = 0.005m, approximately 1/8 inch. You're not going to get better than 1/8 inch tolerance using a steel tape and the human eye, either. If world records havebeen set at your facility, it should have already been measured. I don't think your pool has to be remeasured unless it has undergone reconstruction or you are using a bulkhead. Yes, our pool has been measured in the two outside lanes and center lane which was all that was required prior to January, 2003. Now we must measure all lanes, which we will do using an electronic distance measuring instrument (infrared) on December 16th, courtesy of the Southern Illinois University department of Civil Engineering.

While I don't want to promote any particular brand of laser apparatus, an Internet search produced this Canadian website for a LEICA Disto Lite Laser Distance Measurer which is said to be accurate to the millimeter at the distances we require: www.deakin.com/product.cfm Aprox. US Price:   $449.08 from that page: DISTO lite is a one-person operated unit, measuring distances from 0.3m to over 100m. Measure areas and volumes comfortably and quickly with ±3 millimeter accuracy, even in difficult or unreachable places. This product was also shown at the following US website, but no price was listed. www.forestry-suppliers.com/.../View_Catalog_Page.asp From that page Designed for fast, accurate and efficient measurements, from 1" to over 330" with ±1/8" accuracy! 1/8" equates to a little more than 3mm. I think the tolerance has to be less than 0.5mm. I was hoping for an inexpensive laser measuring device that will meet specs. Maybe it is out there. World records have been set at our facility and the previous measurements seem to have given us sufficient space for two 8 mm touchpads. We'll see. If world records havebeen set at your facility, it should have already been measured. I don't think your pool has to be remeasured unless it has undergone reconstruction or you are using a bulkhead. michael

Mary: You are correct on the .005 distance. Sometime I am going to get the dimensions straight between centemeters and millimeters. (of course my favorite dimensions is furlongs per fortenight - but that is in the English system). But being a gluton for punishment, lets revisit the co-efficent of expansion for a moment. "Steel tapes are standardized at 68 degrees Fahrenheit. The coefficient of expansion on most steel tapes is .0000065 ft per ft and average 0.01ft every 15 degrees over a 100 ft distance. If your water/air temperature were around 83 degrees, you would experience a stretch of your tape of 0.01 ft using a 100 ft tape or 0.02 ft with a 200 ft tape. Thus your pool may appear to be shorter than it really is. Record the measurement without correction for temperature. Also record the temperature. Only if your pool measurement comes up short would the temperature factor need to be considered." We felt this too technical to include in the final version, since the stretch of the tape at higher than the 68 degree standard would not have much impact. The greatest source of measurement error with a tape is sag. " Lets assume as your example the temperature is 83F, then the tape would expand about 5 mm. If you already have a tape that is 5 mm long (the degree of uncerntainty of tape and still meeting spec at that length- this would be on the long side) your 50.00 M pool will measure out at 49.99 (it fails). If I am thinking correctly (and there is no guarantee about that), sag would introduce an error that would make the pool appear to be longer than it is. In a thread on the USMS forum titled "The Losers" on page 4 of discussion, I wrote about trying to calculate the true length when there is sag. "Rob Copeland wrote back "a true 25 meter pool is measured with a 0.1 meter sag (about 4 inches), in the tap, the length on the tape would read 25.001066663 meters" According to Rob, the formula used to calculate the segment of a parabola is s = sqrt+* ln)/(c/2)] Where: s = tape distance, h = midpoint sag and c = true pool length." To me it appears that the sag introduces less error than expansion, but the errors are going the other way from the coefficient of expansion. (co-efficent of expansion errors make the pool appear shorter than it is (if the temperature is warmer than 20C.) sag errors make the pool appear longer than it is. It might be that the errors cancel out each other. I should also say that my head hurts when looking at the equation and I did not recalculate Robs findings (so if I am wrong, I am blaming Rob). I think in the final analysis, there are going to very few pools that are going to come so close to the 50.00M min length. However, I would think that it would be good if we asked for the ambiant temperature when the people make their length measurement (as you seem to suggest), so that we can recalculate a pool that is short by 1-2cm. This may only affect one or two pools in the country, but better to have pools where we can legitimately swim for records than not have them because of bad measuring protocols. To change the subject a little I have not seen seen us provide guidence on the setting up of a pool with a bulkhead. The distance should be measured before the meet begins and it must be measured at the end of each day. If someone is setting up a 50 M pool that has a bulkhead and two standard 8mm touch pads (pads at each end), the pool is being measured with a laser that has a 3mm + or - . What should be the distance from the edge of the pool to the beginning of the bulkhead? I would suggest the distance should be 50.19M. This allows for both pad (0.16M) plus the measurement error. just a thought michael

Anna Lea: We purchased a steel tape with nyon coating (won't rust) at Lowe's. If my memeory is correct we paid less than $30. It is a 200' tape I think. Worked quite well.