This is probably obvious, but I just want to be sure; I looked at the rules and didn't see it specifically addressed. Is it permissible to swim the 10K postal swim and submit the 5K split for the 5K event as well? (Provided the fees for both are paid, of course). I'd prefer to only have to swim a boring workout once. :)
That seems a little goofy to me. Splits count for everything else. Your 1000 split from a 1650 can count for Top Ten listings, etc. I mean, to swim a 10K you have to also swim a 5K, after all. Why should you have to swim them separately?
Splits count for records, not a separate event. You can't take the first 200 of your 400 at Nats (or any other meet) and ask to be given a place/award for the 200 at that meet, even though you may have set a World Record in the 200.
Is it permissible to swim the 10K postal swim and submit the 5K split for the 5K event as well?
No. I've done all five Postal swims a couple times. In both cases much of he activity surrounding the swims was handled by Marcia Cleveland, the USMS open water chair. She never offered to let me combine them. USMS gives you a little extra patch for swimming all five. If they allowed you to collapse the 5k into the 10k, they'd probably also allow you to swim the 3000 as part of the 6000 (the last two legs of the "quintuple crown"). You'd be getting five for three.
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That seems a little goofy to me. Splits count for everything else. Your 1000 split from a 1650 can count for Top Ten listings, etc. I mean, to swim a 10K you have to also swim a 5K, after all. Why should you have to swim them separately?