Open water fitness vs the pool

I can't tumble turn either and find that I do much better comparatively speaking in open water swims that I do pool swims.  I, however, find that in the pool I start out every lap determined to swim fast but by halfway through I am going slow, so my speed issue is the opposite of yours in the pool. When I got into Triathlon about five years ago and was trying to teach myself to swim front crawl and trying to see what I need to do to prepare for open water races vs. lap swimming in a pool I found an article written by a guy that did open water swim races for the coast guard.  He noticed that his open water swim speed was faster than his pool swim speeds at shorter distances.  It took him a few years to figure out what was different but it came down to the fact that in open water he was doing hip driven swimming and when he was in a pool he was doing shoulder driven swimming.  I wasn't sure what these were when I read the article but he had some drill to work on hip driven swimming and he also when through why hip driven swimming was the most effective for open water swimming and any race distance over 400m. 

I did four sprint triathlons last year.  Two were open water swims (although one had the swim canceled due to severe weather) and two were pool swims.  My swim times were in the top 5% on the OWS and they were at about the 25th percentile on the pool swims.  I think my wetsuit helps a lot on the OWS, I think that drafting helps a lot on the OWS, I think being comfortable in open water helps me on the OWS.  I know that the turns kill me on the pool swims.  I practice flip turns for  2-3 weeks leading up to one of the races with a pool swim but was slower with my unfinished technique than I was with the open turns that I have been using for 5 years so I used the open turns on race days.  I think the biggest thing for me is that I don't like wall turns.  Open water doesn't require wall turns so it comes easier to me.