It's incomprehensible that I routinely make 5-6 hours available twice a week for a long ride or brick workout, and, yet, seemingly, it seems impossible to allot just short of 2 consecutive hours to the discipline of swimming for any given day of the training week.
Incomprehensible, until the obvious fact bitch slaps you: swimming long sucks. There I said it. Great swimmers, in particularly the great ultra distance swimmers, must either be the most imaginative people in the world, or whatever is antipodal to thought and imagination. (Phelps might come to mind here by his personal detractors)
The reasoning for this conclusion results from what mental feats (or disasters) that are required to spend 2-6 hours a day staring at the black line of the bottom of the pool or the nothingness of a lake or dark ocean. (People who train in tropical paradises including corral reefs and/or tiger sharks obviously fair better).
Yes Dave Scott famously responded when asked what he thinks about when swimming a 7000 meter workout: "breathing". And therein lies the proof. We all know Dave Scott was a robot. They probably forgot to automate the breathing function into his subconscious.
Also there is the 'easy out-ness' of swimming in the pool. Around 3000 meters you say. Man I'm tired. Time to go 30 yards yonder to the warm hot tub or showers. Cycling doesn't afford this temptation. When 50 miles from home when you realize you are tired you HAVE to say, suck it up loser, get pedaling. Takes immense effort to do this in a pool. Especially when, as stated, you are staring at a black line beneath you.
Yet all this complaining is tangential to my real point. You must, simply, swim long every once in a while. Acknowledge these draw backs and just do it. Like work. Punching the clock. Get it done.
Like cycling, swimming is one of the sports where you can train distances in excess of your race discipline. Bike 150m, then 112 is much more manageable. Swim 7000m, 3800 is a cake walk. (Obviously running does not follow this rule. You should not exceed 22-24 miles before your IM. However, AFTER, in the off season, I surely encourage you to run a 50k or 50 miler to recalibrate your sense of 'long')
So I swam 5000 today (5 x 1000). That's over 1200 more than I'll need for IM. While that's a paltry distance for a real swimmer it does give me a modicum of confidence. All week I had been doing drills and speed work. But in the end, there is no avoiding it, get out there and swim long. Feel the ache and burn and want to stop, and just stop looking at the clock and the tempting locker room door that leads you away from that damn black line of boredom, monotony, and, eventually, madness.