PSA: Indoor to Outdoor swimming: SCY vs LCM paces
Warning: I am a better observer of swimming than I am a swimmer. I'm pretty mediocre in the pool myself, but I've learned a thing or two watching my kids who are real swimmers. :-)
It's this weekend or the past one where the outdoor 50 m pools (LCM = long-course meters) pools open in a lot of the country, and most of us do most (all?) of our indoor training in a SCY pool (= short-course yards = 25 y). The obvious question that comes out is how to translate training paces. If you aren't used to swimming LCM, you will quickly find that your SCY paces are WAY off in the sense that it is a LOT more than twice as long to get to the other side.
This comes from two (and I think 3) things. First a meter is about 10% longer than a yard. Thus, right away, your 100 m time is going to be ~10% longer than your 100 yd time. A lot of people figure that out but still don't understand why they are even slower than that.
The main additional factor is the missing turns. Of course, this depends on how good your turns are. However, a good push-off more than makes up for all but the worst of turns. If you think about it, you'll realize that you're going faster right after the push-off than any other time as you go across the pool. The rest it is a battle to slow down as little as possible. :-)
For very round numbers, you might estimate that you lose 1-2 seconds per turn. Now your calculation is that you have to first add 10% to make up for the distance and add 1-2 seconds per missed turn after that. Last summer, my daughter swam 200 SCY in 2:00.01. (The 1:59.3 in the relay doesn't count....gives her something so shoot for!). So let's do the math for her swimming that same 200 as LCM: (120 sec x 110%) + 2 x (1.5 sec) = 135 seconds, or 2:15. Now, to be honest, I think there is a third factor, which is that most people have their best strokes coming off the push-off and tire or lose a little form (just a little!) in the last 10-15 m of a LCM pool. I think this is observable even at a swim meet with experience competitors. (I discount the very, very best swimmers.) So this 2:15 is probably a bit of an underestimate.
The good news is that there are converters out there that can give you a more specific idea without having to experiment a lot on your own. Two free iPhone apps are "Swim time Converter" and "Swim Times". Even then, however, you are only going to get a good general idea. Why do I say that? Because those are designed for good swimmers, and even the powers that be cannot agree on the exact factors. There is an NCAA one (that is the most commonly used one as far as I can tell) and a USA swimming one. There is also an Australian one and a NFHS (high school) one. They all give slightly different values...which is a lesson that you just can't take them too literally.
The NCAA conversion to LCM for a female swimmer doing a 2:00.00 200 SCY is 2:17.30, but for a male, it is 2:18.73. Apparently the NCAA has decided that men and women turn differently! Regardless, these converters, which can also be found on various web sites, are a good first guess. Most of them, however, will only let you put in distances and strokes that correspond to the usual competitive distances. For anything other than that, you have to make up your own factor, such as I outlined above.
One word of warning about the converters: there are three correspondences that most of the calculators do without you asking:
- 500 SCY ~ 400 LCM
- 1000 SCY ~ 800 LCM
- 1650 SCY - 1500 LCM
This is because these are the closest distances in the usual competitions. It's very rare to have a 400 SCY or 1000 M LCM race, for example.
Regardless, the take-home lessons are.
- Don't feel too discouraged when your 100 LCM pace seems ridiculously slow relative to your SCY. It's not just you.
- There are converters out there that will give you a good idea, but they won't be perfect, particularly because of the turns. If you're in the neighborhood that the converters suggest (maybe a bit slower than they suggest), you are probably fine.
Remember the sunscreen! 
Comments
I've done all my IM training for CDA in an indoor 25 m YCMA pool...and for the swim race rehearsal that I did last week I moved over to the SMU outdoor 50 meter pool - figuring it would give me a more challenging RR. I, of course, discovered what you have laid out - which is I was slower than I anticipated being. I ended up getting the 3800 meters done in 1:06:41 (1:45 pr/100m) - had I done the RR in the indoor pool I would have expected to finish 1:00:09 (1:35 pr/100m).
Thanks for articulating these thoughts for us!
I would like to add a thought/comment to the "its the turns" comment...I got this from Tower 26 (Gerry Rodrigues)...
Its not just the "speed" you get from the push off...that speed carrys over into your first few strokes and for a few strokes/moments you have excellent form...
Gerry actually prefers SCY pools for "less accomplished" swimmers becuase the more turns give them more opportunities to be swimming(and ingrain) good form....
Add approx 15 seconds per 100m long course to convert to short course yards? See http://www.swimmingworldmagazine.com/results/conversions.asp