How to structure an 8-week build for a half-Ironman swim.

Most triathletes I work with have been swimming for years. They put in the yards. They show up to masters practice. They do their open water sessions when the weather allows.

And then race day comes, and they still get out of the water exhausted, disoriented, and thirty seconds per hundred slower than they swim in the pool.

The problem isn't volume. It's structure.

An 8-week build for a 70.3 swim isn't just about getting fitter in the water. It's about training the specific skills, positions, and energy systems that a 1.2-mile open water race actually demands — and those are different from what most pool training develops.

Here's the framework I use.

Before you start: know your baseline

Before week one, you need three numbers:

Your CSS (Critical Swim Speed) — swim a 400 and a 200 for time. Your CSS pace per 100 is approximately: (400 time − 200 time) in seconds. This is your threshold pace — the pace you can sustain for 30+ minutes. All aerobic work in this plan is done at or slightly slower than CSS.

Your current 1500m time — this tells you where your endurance base is. If you can't swim 1500m continuously, extend the base phase below before moving on.

Your target race swim split — work backward from this. If you want to swim 35 minutes for 1.9km, you need to average about 1:50/100m. Know the pace.

The 8-week structure

This plan is organized into three phases. Don't skip ahead.

Phase 1: Aerobic foundation (Weeks 1–3)

The goal here is not speed. The goal is building your aerobic base at controlled intensity and cleaning up the technical inefficiencies that cost you energy over distance.

Weekly volume: 3 sessions, 2,000–2,500m per session Intensity: Mostly Zone 2 — comfortable, conversational pace

Session structure:

• Warm-up: 400m easy + drill set (focus on catch and rotation)

• Main set: Long aerobic intervals — e.g. 5 × 400m at CSS +10 seconds, 30 sec rest

• Cool-down: 200m easy

Key drill work to include:

• Catch-up drill for stroke timing

• Fingertip drag for high elbow recovery

• Side kick drill for body rotation

Don't skip drills in this phase. The habits you build here carry into the race-specific work later. Bad habits at easy pace become disasters at race pace.

Phase 2: Race-specific skills (Weeks 4–6)

This is where most training plans fall short. Pool work is fine for building fitness, but a 70.3 swim has variables that pools don't replicate. This phase addresses them directly.

Weekly volume: 3 sessions, 2,500–3,000m per session Intensity: Mix of CSS and above-threshold work

Skill 1: Sighting Add sighting every 6–10 strokes in your pool sessions. Lift eyes only — not your head — and return immediately. Practice the pattern until it costs you almost nothing in stroke rhythm.

One session per week, swim the entire main set with regular sighting built in. You'll notice your pace drop by 3–5 seconds per 100 initially. That's normal. By week 6, it should cost you almost nothing.

Skill 2: Drafting position If you have a training partner, practice swimming directly behind their feet — 30–50cm back. Legal drafting in triathlon can save 20–30 seconds per 100m. This is a skill you train, not luck you rely on.

Skill 3: Mass start simulation This one is uncomfortable and therefore usually skipped. It shouldn't be. Start two or three swimmers from the same wall at the same time, in adjacent lanes, without space. Get used to contact. Get used to disrupted breathing. Get used to finding your rhythm after being hit.

Skill 4: Wetsuit swimming If you race in a wetsuit, train in it at least once a week during this phase. Wetsuit swimming changes your position in the water, your shoulder range of motion, and your stroke rate. Racing in a wetsuit you've never trained in is asking for problems.

Phase 3: Race prep and taper (Weeks 7–8)

Week 7 — peak week: This is your highest volume and intensity week. It should feel hard.

• One long swim of 3,500–4,000m (for 70.3; adjust if training for sprint)

• One race-simulation session: swim your target race distance continuously, in open water if possible, at goal race pace

• One quality session: 10 × 100m at race pace, short rest

Week 8 — taper: Volume drops by 40%. Intensity stays. The goal is to arrive at race day feeling rested but sharp — not sluggish from too much rest.

• Session 1: 1,500m easy, technical focus only

• Session 2: Short quality set — 6 × 100m at race pace, full recovery

• Session 3 (2 days before race): 800m easy, some sighting practice, race-day warm-up rehearsal

Race morning

This is often completely ignored in training, which is a mistake.

Your race-morning warm-up determines how the first 200m feel. And the first 200m of a mass start triathlon swim determine a lot about the next 30+ minutes.

If the race allows water warm-up, take it. Swim 200–400m easy, include 4–6 race-pace strokes to activate your neuromuscular system, and practice your breathing pattern. Get your goggles positioned and your wetsuit settled before you're on the start line.

If there's no water warm-up, do dry-land activation: arm swings, shoulder rotations, a few minutes of elevated heart rate. Your first strokes will still feel hard — accept that, don't fight it, settle into your pace by 200m.

The honest truth about 70.3 swim preparation

Eight weeks is enough to make a meaningful difference. It is not enough to fix everything.

If your technique is fundamentally broken, eight weeks of volume won't fix it — it will just ingrain the bad habits more deeply. If that's you, spend the first two weeks doing nothing but drill work and short sets, not yardage.

If your aerobic base is solid and your technique is decent, this framework will produce a noticeable split improvement. Every athlete I've run this with has seen somewhere between 2 and 9 minutes off their previous 70.3 swim.

Start with the baseline numbers. Trust the phases. Do the sighting work even when it's boring.

That's how you stop surviving the swim and start racing it.