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?
Former Member
Cool discussion -- I am learning a lot. Keep it going :)
'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.
Those things based on radio waves in the consumer market are what I'm referencing. Products such as this:
Irwin Laser Tape at Amazon.com
Those _are_ around $50, and yes, they _are_basically worthless for anything more detailed than an inch or two.
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.
Well, I've measured a couple of pools with the Disto Pro, and signed my name to several pool length certification forms as fully believing that my measurements were accurate to the tolerances specified by USMS.
No, I'm not a certified surveyor, and never claimed to be. I feel a whole lot more confident with our laser measurements than I was with any metal tape measurements we did before.
-Rick
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.
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:
www.servco1.com/con_ts.htm
or:
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.
www.auto-met.com/.../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.
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.
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.
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.
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.
I wonder if someone will eventually come up with a method of measuring pools using GPS. With the technology getting more precise, could it be only matter of time? Just a thought . . . nothing more!
Originally posted by Phil Arcuni
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.
Yeah, error theory can be tough even for a fair amount of left-brainers to wrap their mind around. With right brainers, you can pretty much forget it.
It does not make much of a difference, probably till you get to around an inch...
Then again, if they want to be that accurate, then they have to go away from the touch pads, and come up with some sort of a photo finish... Of course, that wouldn't work with flipturns, would it??? ;)
The more I think about how it all works... Even though there is a big disparity (or in my professional opinion HUGE disparity) between what the rules say, and how it's actually being done, they're probably fine - talking practically.
When you look at it theoretically, it's all goofy.... but hey, it works.
Watching it, for me it's got that nails on the chalkboard effect, so, if or till they ask me to help out, I just have to turn the other way.
You know, it's like watching a lap swimmer with a snorkle, paddles and fins doing laps with open turns, and calling it competetive training and saying they're gonna get a fastskin to help them get faster.
I'm also willing to bet that most of the bulkheads get places in a much mpore accurate position than, with current methods being used, are able to measure them.
