I'm a Clyde (235 lbs) and did my first triathlon last year. It was a sprint distance so the swim was 800 meters as well. There really isn't any substitue for time in the water.........ususally most pools will set aside at least one lane for lap swim even when the kids are there. Once sugestion I would make is to get a full lenght spring suit. The suit will give you a great deal more buoyancy and make the swim a lot easier. That being said from a safety standpoint if you can't get swim time in I'd see if they have a duathlon. It would really suck to do all your hard training and have to DNF in the swim.