I have been working for my professor all day (well - a dinner break) and I am not yet done with my tasks - so just briefly:
I did make my two days of swimming this week so that day 2 could be the variation workout (i.e. not the .6 mile lap swim). Here is what I ended up with and think will work for the summer - hopefully I will get stronger as time goes by, because this was pretty tough.
2 full laps of freestyle or front stroke or crawl (whatever its called)
2 full laps of backstroke (water up my nose!)
1 full lap of kickboard (my legs are so weak)
(full lap means back to where I started)
so it ends up to be 1000 yards - just 50 short of the 21 lap swim :)