One with an actual coach on deck. And a team atmosphere is even better.

I swam in squads when I was a kid and competed in swim competitions from primary school all the way through high school.Once I started triathlon training I couldn't bring myself to swim with a squad,partly because I was in the hotel industry and my work hours were very anti-social and partly because the squad thing no longer interested me.This year marks 30 years since my first Ironman and I still refuse to swim in a squad or even share workouts with friends.I can't bring myself to follow any of the overly complicated swim sets that are part of the world of swimming instead I swim pretty much continuously in every session only stopping to attach whatever swim aid I want to use.Yes I do speedwork and yes I do drills but they are all part of the almost non-stop sessions that I do.I tried to watch the clock last month for some more traditional speedwork sessions but that lasted two days before I lost interest.

The most effective training "secret" I personally have is that I am able to train hard by myself all the time,something that other triathletes have told me they can't do without the squad or coaching environment pushing them.If I were to align myself with any of the methods of well known coaches out there I guess it would be Brett Sutton.

I still can't run to save my life though...
.
.

 You should EXCEL at running if you are super self-motivated and like to train solo!

Running well for the typical AGers is all about committing to putting in LOTS of easy miles and then a small dose of good, hard speedwork on top, consistently. You don't need a coach to monitor your technique, and you don't need to feel the technical challenges of group race/riding!

Give me a pool under 20°C and a clock on the wall. That's enough for me.

Yes, I hear you. But you are extremely experienced in the sport. What I am trying to say rather ineloquently is that attempting to become a good or even just competent triathlon swimmer by reading a book, viewing videos, or signing up for an online program is not nearly as effective as on-deck coaching and being part of a squad of swimmers just like you. It creates an effective learning and positive competitive atmosphere.

My biggest improvement have come from long continuous swims, usually 7K-10K long, incorporating the last 2K using the largest paddles I could find, to gain some strength. I have no formal training, and no swimming background. I started in 2016 with youtube videos, and did a bunch of anything but real swimming. Then I tried intervals like 50's and 100's, and seemed to be stuck at 2:00/100 forever. When I calculated how much time I was wasting at the end of the pool, I decided screw it, if I'm going to suck, I might as well suck at being able to swim 2.4 miles continuous. I fell in love with cranking my swim radio shuffle, and just swimming my ass off, as long and hard as I could. It didn't take long before I was going 5K three times a week, and now I'm hitting 10K two to three times a week. I'm still not fast, but I'm a lot better than I thought I could ever be, that first year or so. I've been hitting my 2.4 mile split at the pool @ 1:11 - 1:14 . I'm a loner, and don't train with anyone. I swim early in the morning, and usually have the pool to myself.

---

Athlinks / Strava

I've had similar experience with the dreaded 'long-continuous swim' as you.

I did mainly all (hard) intervals for my first several years of swimming as a no-talent AOS swimmer. Was rare for me to swim anything longer than a 500, and most of it was 100s-200s, on various rest from 5s to 20s. Kept the intervals on a pretty good effort too, definitely Z3+.

Definitely didn't make the vaunted breakthroughs that everyone here seems to crow about with intervals. Got to like 1:47/100 and got stuck there. Granted, I wasn't swimming any more than 10k/wk, but it wasn't like the intervals were making me any faster in the long run.

In contrast, long continous swims, like 75-90 mins seem to really boost my swimming at all distances. I do swim these hard enough that the last 15 minutes are pretty tough, I'm def not just z1 easy the whole way. These even help if I do 'em on the Vasa erg, but they're tough and annoying enough that I hate doing them even though I have no excuse not to!

I use swimplan.com

New Zealand based outfit. Top notch.