Page 1 of 2 12 LastLast
Results 1 to 20 of 31

Thread: How do you measure the length of a pool?

  1. #1
    Very Active Member
    Join Date
    Jan 2002
    Location
    Menlo Park, CA
    Posts
    114

    How do you measure the length of a pool?

    I would like any suggestions on how to do this with a tape. (This is pretty non controversial, right?) I have spent a career trying to figure out how to measure things, and I am curious. From the comments in this group, the problems I mention below must have been solved.

    First you stretch the tape along the side of the pool. That would work well, but how are you sure you are aligned with the walls, or that the walls are square? Also, you need to measure in several lanes, rather than the side.

    So you get in the pool and hold the tape against the walls, 1 foot below water level. The problem is that the tape sags, and any measurement will overestimate the length of the pool by a significant amount. You could pull the tape tighter, but I suspect before the tape gets tight enough, your tape will stretch or break. (I used to assign that as an intro physics problem). I suppose you could build a support structure across the pool, but that would be a pain in the neck, and you would have to move it from lane to lane.

    Getting the water out of the pool would make that support structure easier, but the water weighs a lot. It almost certainly causes the walls to bend outward, especially in the deeper pools. (How do the people who design above ground, temporary competition pools do it?) I don't know how much the walls will move, but how do you account for that? (and by the way, how do the masons make sure their plaster/tiling is correct in an empty pool?)

    Here is an idea - you lower the water level by a foot or so, and build a *floating* support structure for the tape. I think that would solve most of the problems. Has anyone done that?

  2. #2
    Active Member GZoltners's Avatar
    Join Date
    Jan 2002
    Location
    Durham, NC
    Posts
    76
    How about measuring along the top of a competitive lane line? Those get cranked pretty tight and are also floating.

    How about let the measurement instrument sag and use hyperbolic functions to determine the length? You can measure the drop from vertical using a laser and a ruler.

    Swim fast,
    Greg

  3. #3
    Very Active Member jim thornton's Avatar
    Join Date
    Jan 2002
    Location
    A, A
    Posts
    2,106
    Blog Entries
    261
    Phil,

    I recently was asked to give a toast in celebration of the immortal memory of Robert Burns, poet laureate of Scotland. In the course of my research, I discovered that Burns--the so-called Ploughman's poet who spent a good deal of his life as a farmer--came up with a classic method of measuring the weight of a hog. I realize this is somewhat different from measuring the length of a swimming pool, but perhaps his method might be somehow adapted to the latter pursuit.

    In any event, here's what Burns suggests:

    (1) Get a perfectly symmetrical plank and balance it across a sawhorse.

    (2) Put the hog on one end of the plank.

    (3) Pile rocks on the other end until the plank is again perfectly balanced.

    (4) Carefully guess the weight of the rocks.

  4. #4
    Participating Member
    Join Date
    Feb 2002
    Location
    Minneapolis, MN
    Posts
    14
    I'm curious too.

    The University of Minnesota hires someone for the big meets. They are "on call" for appropriate measurements. I was told that they take many factors into consideration including humidity and water temp. Hmmm, doesn't the pool either measure-up or not? We were also told that the going rate for the "expert" to come in for a Sunday Masters meet is probably around $700. Even if they are 7 X high, who wants to pay that???

  5. #5
    Very Active Member sparx35's Avatar
    Join Date
    Sep 2003
    Posts
    457
    this should have been done when built..the pool regs require this....seek the installer...!!
    ps sorry this reply is a few yrs late....ive bin outta town...
    live to swim,,,,,swim to live

  6. #6
    Very Active Member
    Join Date
    Jul 2003
    Posts
    101
    Actually I saw them measuring the pool at Nationals. It appeared that they were floating the tape on some sort foam blocks in the lane and then pulled the slack out to take the measurement. I only saw them in the end lane, not sure how (or if the do) measure the center also.

  7. #7
    Very Active Member knelson's Avatar
    Join Date
    Mar 2003
    Location
    Seattle, WA
    Posts
    7,282
    Blog Entries
    534
    Step one: throw away tape.
    Step two: buy laser.

  8. #8
    Very Active Member Conniekat8's Avatar
    Join Date
    Aug 2003
    Location
    Mission Viejo, CA
    Posts
    1,412

    Re: How do you measure the length of a pool?

    Originally posted by Philip Arcuni
    I would like any suggestions on how to do this with a tape. (This is pretty non controversial, right?) I have spent a career trying to figure out how to measure things, and I am curious. From the comments in this group, the problems I mention below must have been solved.

    First you stretch the tape along the side of the pool. That would work well, but how are you sure you are aligned with the walls, or that the walls are square? Also, you need to measure in several lanes, rather than the side.

    So you get in the pool and hold the tape against the walls, 1 foot below water level. The problem is that the tape sags, and any measurement will overestimate the length of the pool by a significant amount. You could pull the tape tighter, but I suspect before the tape gets tight enough, your tape will stretch or break. (I used to assign that as an intro physics problem). I suppose you could build a support structure across the pool, but that would be a pain in the neck, and you would have to move it from lane to lane.

    Getting the water out of the pool would make that support structure easier, but the water weighs a lot. It almost certainly causes the walls to bend outward, especially in the deeper pools. (How do the people who design above ground, temporary competition pools do it?) I don't know how much the walls will move, but how do you account for that? (and by the way, how do the masons make sure their plaster/tiling is correct in an empty pool?)

    Here is an idea - you lower the water level by a foot or so, and build a *floating* support structure for the tape. I think that would solve most of the problems. Has anyone done that?
    Well, It just so happens that I'm a Land surveyor (in addition to being a civil Engineer), we;re experts, and the last word on doing theese things (according to the laws and most civil codes, and according to the Professional Land Surveyors Association etc...).
    I've already told the guys at the SPMA I'll look at the requirements, and write down the procedure and recommend how it should be done etc...
    I'd love to write more about it, but I'm short on time right now.
    -Connie
    I'd rather be swimming http://www.mastersmvnswim.org/

  9. #9
    Very Active Member Conniekat8's Avatar
    Join Date
    Aug 2003
    Location
    Mission Viejo, CA
    Posts
    1,412
    Originally posted by knelson
    Step one: throw away tape.
    Step two: buy laser.
    Nope. No Lasers.
    For one, you can't do it accureately enough with a home depot laser... There is pretty severe signal dispersion and mis-reflection near water. You get a ton of false readings.

    You may have meant the EDM (Electronic distance meter) which works based on radio waves... It's very different from a laser.
    But, no need to buy a $50,000 dollar piece of equipement.
    -Connie
    I'd rather be swimming http://www.mastersmvnswim.org/

  10. #10
    Very Active Member Conniekat8's Avatar
    Join Date
    Aug 2003
    Location
    Mission Viejo, CA
    Posts
    1,412
    Originally posted by GZoltners
    How about measuring along the top of a competitive lane line? Those get cranked pretty tight and are also floating.

    How about let the measurement instrument sag and use hyperbolic functions to determine the length? You can measure the drop from vertical using a laser and a ruler.

    Swim fast,
    Greg
    Each tape, when properly tensioned has a factor for it's own 'catenary sag' that can be calculated.
    The problem with tapes around pools is that you can't tension it properly, and what you end up with by just hand pulling is anyone's guess.

    If it's to be done with a tape, ot should be done with 4 range poles, an offset tape (layiong flat on the side of the pool, an no worries about the sag) and couple of right angle prisms... But, again, it has to be done properly.
    it's called 'station and offset' measuring, and it would be much more precise and accurate than what I see being done now.
    -Connie
    I'd rather be swimming http://www.mastersmvnswim.org/

  11. #11
    Very Active Member Conniekat8's Avatar
    Join Date
    Aug 2003
    Location
    Mission Viejo, CA
    Posts
    1,412
    And, in gheneral, I've noticed that the USA Swimming requires that the pool be certified by a professional land surveyor, or a civil Engineer qualified to perform Land Surveys (not all of them are).
    In a nutshell, by making that requirement they got it right when it comes to getting the pool certified.
    This do-it-yourself measuring th pool is tanamount to a lap swimmer claiming that he'll get to the olympics by doing laps, not realizing that that there's little (a lot) more to it than just swimming laps.
    -Connie
    I'd rather be swimming http://www.mastersmvnswim.org/

  12. #12
    Active Member
    Join Date
    Jan 2004
    Location
    Keystone Heights, FL
    Posts
    36
    Cool discussion -- I am learning a lot. Keep it going

  13. #13
    Very Active Member
    Join Date
    May 2004
    Location
    Woonsocket
    Posts
    148
    Originally posted by Conniekat8
    And, in gheneral, I've noticed that the USA Swimming requires that the pool be certified by a professional land surveyor, or a civil Engineer qualified to perform Land Surveys (not all of them are).
    In a nutshell, by making that requirement they got it right when it comes to getting the pool certified.
    This do-it-yourself measuring th pool is tanamount to a lap swimmer claiming that he'll get to the olympics by doing laps, not realizing that that there's little (a lot) more to it than just swimming laps.
    Suppose you are running a 3 day state meet in a pool with a bulkhead. To be correct you would have to measure the pool 4 times. Can you give us a very rough estimate on what it would cost to have a qualified Land Surveyer to do that many measurements?
    Howard

  14. #14
    Very Active Member
    Join Date
    Feb 2002
    Location
    Watertown, MA
    Posts
    520
    We do it was laser here in New England. We picked up a Leica Distro Pro 4a laser, which has accuracy better than required by USMS rules. I put it together on a contraption that involves some magnetic levels and a cutting board, so that you can mount the laser (and a target) in the gutter, flush to the wall, on each end, and get an accurate measurement. We measured an 8-lane 50 meter pool in about 10 minutes total.

    I don't have the device with me now... I should take some digital pictures of the rig and post them. The laser device itself cost about $600.

    Don't try to use anything that's based on radio waves... those things, as far as I know, are barely accurate to an inch. (These are the $50 devices you find at Home Depot.)

    -Rick

  15. #15
    Very Active Member Conniekat8's Avatar
    Join Date
    Aug 2003
    Location
    Mission Viejo, CA
    Posts
    1,412
    Originally posted by Howard


    Suppose you are running a 3 day state meet in a pool with a bulkhead. To be correct you would have to measure the pool 4 times. Can you give us a very rough estimate on what it would cost to have a qualified Land Surveyer to do that many measurements?
    It depends on what part of a country you're in, as their hourly rates vary drastically, depending on a local economy and local real-estate values.

    For the measurements, the stuff a surveyor would have to do is pretty basic (compared to the other stuff they normally do), they would probably charge you about an hour to do this, it would be two guys for an hour... (it would take less then that, but most would charge a minimum of an hour) each time they come out.
    You want to hire someone who is close, not someone who would have to drive two hours to get to the pool.

    In Southern California, in LA area, a 2 man crew wouldcost around $180 per hour, 200 miles away, the prices can be down to a $100/per hour for a 2 man crew.
    In other parts of the country, with different rates, it could be as low as $50 per hour for a 2 man crew.

    If it's on a weekday, near the end of the day, and you make friends with a local surveyor, they may be able to just swing by and do the measurememnts really quickly for you... as a donation, or as a favor.
    -Connie
    I'd rather be swimming http://www.mastersmvnswim.org/

  16. #16
    Very Active Member Conniekat8's Avatar
    Join Date
    Aug 2003
    Location
    Mission Viejo, CA
    Posts
    1,412
    Originally posted by osterber
    We do it was laser here in New England. We picked up a Leica Distro Pro 4a laser, which has accuracy better than required by USMS rules. I put it together on a contraption that involves some magnetic levels and a cutting board, so that you can mount the laser (and a target) in the gutter, flush to the wall, on each end, and get an accurate measurement. We measured an 8-lane 50 meter pool in about 10 minutes total.

    I don't have the device with me now... I should take some digital pictures of the rig and post them. The laser device itself cost about $600.

    Don't try to use anything that's based on radio waves... those things, as far as I know, are barely accurate to an inch. (These are the $50 devices you find at Home Depot.)

    -Rick
    I'm quite familiar with Leica products, as well as with Geodimiter, Trimble, Carl-Zeiss and many others.
    This is a typical piece of equipement that a surveyor would bring with him:
    http://www.servco1.com/con_ts.htm
    or:
    http://www.servco1.com/theodolites.htm or: http://www.servco1.com/ts.htm

    'those things based on radio waves' you're talking about are sophisticated pieces of equipement that run in the range of $ 50K to 80K or more, and are used for high precision surveys. Not something that you pick up at Home Depot, not something that's even sold there.

    It's Disto-Pro (drop the "r"), as in Distomat-Pro, which is a Low end construction grade piece of equipement.
    http://www.auto-met.com/leica/distopro.htm
    (still, better than the tape) based on the written USMS requirements of the required precision of the measurement, a construction grade instrumen't won't do. Then again IMO, those requirements need to be rewritten... By a professional.
    I read and re-read and re-read the USMS rules on the measurements, and I can guarantee you that the device you have does not fit the rules... Even though the device may be adequate for what USMS realistically needs, it's the way the rules are written.

    Back to the Disto-Pro, still, you have the issue of laser near the water, and also, even though the equipment claims to be +/- 1.5mm, depending on how you line it up, you're going to get bigger discrepancies than that.
    -Connie
    I'd rather be swimming http://www.mastersmvnswim.org/

  17. #17
    Very Active Member
    Join Date
    May 2004
    Location
    Woonsocket
    Posts
    148
    Originally posted by Conniekat8


    It depends on what part of a country you're in, as their hourly rates vary drastically, depending on a local economy and local real-estate values.

    For the measurements, the stuff a surveyor would have to do is pretty basic (compared to the other stuff they normally do), they would probably charge you about an hour to do this, it would be two guys for an hour... (it would take less then that, but most would charge a minimum of an hour) each time they come out.
    You want to hire someone who is close, not someone who would have to drive two hours to get to the pool.

    In Southern California, in LA area, a 2 man crew wouldcost around $180 per hour, 200 miles away, the prices can be down to a $100/per hour for a 2 man crew.
    In other parts of the country, with different rates, it could be as low as $50 per hour for a 2 man crew.

    If it's on a weekday, near the end of the day, and you make friends with a local surveyor, they may be able to just swing by and do the measurememnts really quickly for you... as a donation, or as a favor.
    The added cost of up to 700+ per meet might be enough to keep a smaller local meet from actually being held. I don't know who wrote the original rules but it may be that they didn't want to write them in such a way that the meet host was going to have to face the choice of having the meet or having the pool measured. On the other hand, given the way it's written and how hard it is to accurately measure with a tape it's questionable if the results are worth the paper they are written on.
    Howard

  18. #18
    Very Active Member Conniekat8's Avatar
    Join Date
    Aug 2003
    Location
    Mission Viejo, CA
    Posts
    1,412
    Originally posted by Howard


    The added cost of up to 700+ per meet might be enough to keep a smaller local meet from actually being held. I don't know who wrote the original rules but it may be that they didn't want to write them in such a way that the meet host was going to have to face the choice of having the meet or having the pool measured. On the other hand, given the way it's written and how hard it is to accurately measure with a tape it's questionable if the results are worth the paper they are written on.
    You got my point there!!!
    One of the things I have to do, that I haven't gotten around to yet is figure out just how much time difference an inch or half an inch or few milimeters make, time wise at certain swimming velocities, and from there come up with a reasonable set of tolerances in the pool length measurements.
    Measurements will NEVER be exact, there is always some slop in them. The important part is to come up with an acceptable +/- tolerances. Yes, that would mean that some of the finishing times cary a certain level of uncertainty.

    There is a a large volume of literature written on 'error theory' and how to make adjustments for them etc... Something I had to study at length for the business I'm in.

    One of toughest thing for 'lay' people to understand is that the measurements and results will never be 'exact', but that they're still good, and comparative.

    Explaining all this in detail can be a very lengthy process... I wouold like to, but I really can't afford the time to get into an in depth discussion about it here. I'm sorry.
    -Connie
    I'd rather be swimming http://www.mastersmvnswim.org/

  19. #19
    Very Active Member
    Join Date
    Mar 2002
    Location
    Menlo Park
    Posts
    328
    A long time ago I participated in this discussion, arguing that an excessive attention to pool length was both unnecessary and harmful to the availability of pools and competitions.

    Boy, did I get slammed!

    I followed that up by arguing that measuring a pool to the accuracy desired was both difficult and expensive, and I implied that almost everyone was unqualified to do it (nothing has changed my mind on that, either.)

    Once again, I was at my most controversial (evidently (and except for the very long ago 'America' thread).)

    After the pool length controversy, I have seen at least one local pool no longer able to host sanctioned Masters events, even though it had been doing so for at least 20 previous years (and I think USS continues to hold meets there.) Every local pool that hopes to host a meet has been measured with a steel tape by local USMS officials.

    I now take the attitude that most people seem satisfied with the method of measurement, and there are pools that can still host meets. The last thing we need is to remeasure pools and either disqualify more pools or make the whole process more expensive.

    This is one case where the right way is the wrong way.

  20. #20
    Very Active Member
    Join Date
    Mar 2002
    Location
    Menlo Park
    Posts
    328
    You got it, Connie, but this is a very unresponsive group to any even-not-very sophisticated uncertainty analysis. Believe me, I tried.

    And you are also right in your intuition that it does not make much of a difference -- even in the most extreme case the effect is in the thousandths of a second.

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •