How to use this planner
What this tool calculates
This planner solves two linked spearfishing problems: how long you must rest between dives and how long your float line needs to be. Enter your dive time and depth for the quick result, or log a full session to see each dive's required surface interval, session totals, and a safety flag for any dive that breaks the 2:1 AIDA minimum.
Method & Formulas
Surface Interval Rules
The minimum surface interval is calculated two ways, and the larger of the two is used:
1. Time-based (AIDA): SI_min = dive_time × 2 (seconds)
2. Depth-based (for dives > 30 m): SI_min = (max_depth_m ÷ 5) × 60 seconds
Recommended (spearfishing): SI_rec = dive_time × 3 (or user-selected multiplier)
Source: AIDA International (Association Internationale pour le Développement de l'Apnée) and DAN Southern Africa dive medicine guidelines.
Float Line Length
Float line length = max_depth × multiplier
Standard multiplier: 1.5× (reef, bluewater)
Kelp/rock multiplier: 1.33× (depth + one-third)
Pelagic/tuna multiplier: 2.0×
Source: Verified against expert spearfishing guides — the 1.5× rule is the widely-cited industry standard; the 1.33× ("depth + a third") is used by South African spearo practitioners.
Steps
- Quick Planner: Enter your dive time (seconds), max depth, effort level, and float line scenario. Results update instantly.
- Session Log: Add each dive in order. Set your session window (total hours available) and your preferred safety multiplier. Hit "Calculate Session" to get a table with per-dive intervals and a go/no-go for the window.
- Export: Download a CSV dive log, print a clean summary, or share your session link.
When & why you'd use this
Before a session: Plan how many dives fit in your window, and what intervals to keep. Avoid the temptation to rush back down when fish are stacked — the numbers keep you honest.
After a session: Log dives retrospectively to spot intervals that were too short. Any dive flagged in red had a surface interval shorter than the AIDA 2:1 minimum — a real decompression and blackout risk.
Float line purchase: Enter the deepest depth you plan to hunt and see the minimum line length to buy. A line that pulls you toward the surface while you're on the bottom is a serious hazard.
⚠ These are planning estimates based on published guidelines, not a medical tool. Every diver is different. Never dive if you feel discomfort, dizziness, or breathlessness regardless of what the timer says. Always dive with a buddy. This tool does not replace qualified freediving instruction from a certified agency (AIDA, SSI, PADI Freediving, Molchanovs).
Frequently Asked Questions
How long should my surface interval be between freedives? +
The AIDA-recommended minimum surface interval is 2× your dive time. A 90-second dive means at least 3 minutes on the surface. For dives deeper than 30 m, use the depth-based rule: max depth (m) ÷ 5 = minimum minutes on the surface — so a 40 m dive requires an 8-minute interval. For spearfishing with real exertion, most coaches recommend 3× dive time as your working rule. Never dive again if you still feel breathlessness or a racing pulse regardless of the clock.
How long should my spearfishing float line be? +
The standard rule is at least 1.5× your maximum dive depth. Diving 15 m? Minimum 22–23 m of line. In rocky reef or kelp, the "depth + one-third" rule (1.33×) is used by many South African spearos. For bluewater tuna or large pelagics, over-rig with 2.0× or more — a fish that sounds can drag a float under and lose your whole rig. The line must never pull you toward the surface while you're working the bottom.
What is the 3:1 surface interval rule in spearfishing? +
The 3:1 rule means resting at least 3 minutes at the surface for every 1 minute underwater. It is a conservative extension of the AIDA 2:1 minimum. Spearfishing coaches favour the 3:1 ratio because hunters push harder and work the bottom more than pure freedivers, which elevates CO2 and depletes oxygen faster. The first 30–60 seconds after surfacing should be active CO2 flush breathing; the remaining time is relaxed breathe-up before the next dive.
Can freedivers get decompression sickness (DCS)? +
Yes. Freedivers can develop DCS — known historically among Polynesian pearl divers as "Taravana" — from repetitive deep dives with short surface intervals, even without compressed air. Risk rises significantly above 30 m with inadequate rest. DAN Southern Africa recommends limiting dives deeper than 50 m to one deep dive per day, and beyond 55 m to once per 24 hours. Following the 2:1 (minimum) or 3:1 (recommended) surface interval rule dramatically reduces DCS risk at recreational spearfishing depths of 5–25 m.
What is the correct breathe-up technique before a freedive? +
The breathe-up is 1–2 minutes of slow, diaphragmatic breathing at the surface before submerging. It lowers your heart rate, balances blood gases, and activates the mammalian dive reflex. Never hyperventilate — it lowers CO2 without raising O2 content, removes the urge to breathe, and dramatically raises the risk of shallow-water blackout. A safe breathe-up ends with a full but relaxed inhale, not a strained one. If you feel dizzy, lightheaded, or notice tingling — stop and wait longer.
How many dives can I safely do in a 3-hour session? +
It depends on your dive time and depth. Using the 3:1 rule, a 90-second dive at 15 m needs 4.5 minutes rest. Each dive cycle = 1.5 min (dive) + 4.5 min (rest) = 6 min per cycle. In a 3-hour (180 min) window, that's roughly 30 dive cycles — though fatigue, current, and surface conditions will reduce that in practice. Use the Session Log above to plan exactly how many dives fit in your window given your actual times.