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?
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Former Member
Let's say it takes 15 seconds to swim across a 25 Yard pool... (we do that in practice on 25Y sprints)
15s/25Y=0.6 Yards per second
That converts into 1.8 feet per second.
Now, the times are measured in 1/100's of a second...
At the above velocity a swimmer will tavel 0.18 feet in 1/10th of a second
and will travel 0.018 feet (or 4.5 mm) in 1/100th of a second.
Measuring something to 0.02' or 0.01' in surveying is considered high precision, and for the USMS purposes would be cost prohibitive. Plus, with the touch pads there is a lot more slop than that just in the way they are mounted...
The real question is, considering th equipement used, the pools the touchpads etc, what would be reasonable uncertainty in the finishing times for the athletes. Is +/- 0.02" in time an acceptable uncertainty? +/- 0.2" would give a total of 0.04" in time, which would translate into a pool length tolerance of 4*0.018'=0.072 or around 18mm (almost 2CM). With the touchpads and a tape strapped across the pool, it's going tpo be very hard to determine the pool lenght (at the time the events had been swum) to that level.
Touchpads bow, bulkhead may shift, and there are errors in measurements, and I've seen the condition of the tapes that are often used, kinks, rust etc... I wonder if the tapes were to get calibrated, how they'd hold up.
Realistically, from what I've seen I would make an guesstimate that the measurements that are being perfoprmed right now are around +/- 2 cm (4cm or just under 2" total potential length error.)
But that's just the guesstimate. To be able to trell for sure, we'd have to have a set of comparative measurements done.
Anyway, the question remains, what is the acceptable uncertainty in the finishing times? That will determine how, and to what precision the pools need to be measured.
And yes, there will always be uncertainty in finishing times.
Sorry to burst some people's bubbles. Just because something is measured to 1/100th of a second, doesn't mean that the measurement is necessary reflective of reality, as we see it.
Hey Jeff,
Hypothetically speaking... Do you have access to a theodolite or a total statin or something similar, and if your local pool(s) needed to be measured, would you be able to donate that service?
What are the 2 man survey crew hourly rates in your area?
Let's say it takes 15 seconds to swim across a 25 Yard pool... (we do that in practice on 25Y sprints)
15s/25Y=0.6 Yards per second
That converts into 1.8 feet per second.
Now, the times are measured in 1/100's of a second...
At the above velocity a swimmer will tavel 0.18 feet in 1/10th of a second
and will travel 0.018 feet (or 4.5 mm) in 1/100th of a second.
Measuring something to 0.02' or 0.01' in surveying is considered high precision, and for the USMS purposes would be cost prohibitive. Plus, with the touch pads there is a lot more slop than that just in the way they are mounted...
The real question is, considering th equipement used, the pools the touchpads etc, what would be reasonable uncertainty in the finishing times for the athletes. Is +/- 0.02" in time an acceptable uncertainty? +/- 0.2" would give a total of 0.04" in time, which would translate into a pool length tolerance of 4*0.018'=0.072 or around 18mm (almost 2CM). With the touchpads and a tape strapped across the pool, it's going tpo be very hard to determine the pool lenght (at the time the events had been swum) to that level.
Touchpads bow, bulkhead may shift, and there are errors in measurements, and I've seen the condition of the tapes that are often used, kinks, rust etc... I wonder if the tapes were to get calibrated, how they'd hold up.
Realistically, from what I've seen I would make an guesstimate that the measurements that are being perfoprmed right now are around +/- 2 cm (4cm or just under 2" total potential length error.)
But that's just the guesstimate. To be able to trell for sure, we'd have to have a set of comparative measurements done.
Anyway, the question remains, what is the acceptable uncertainty in the finishing times? That will determine how, and to what precision the pools need to be measured.
And yes, there will always be uncertainty in finishing times.
Sorry to burst some people's bubbles. Just because something is measured to 1/100th of a second, doesn't mean that the measurement is necessary reflective of reality, as we see it.
Hey Jeff,
Hypothetically speaking... Do you have access to a theodolite or a total statin or something similar, and if your local pool(s) needed to be measured, would you be able to donate that service?
What are the 2 man survey crew hourly rates in your area?
