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?
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.
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
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???
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...:D
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.
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.
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.
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.
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.
