⚙️ Conditions Assessment Logic
GO bar (Fred's thresholds)
Wind < 10 kt · Swell < 1.0 m · Viz ≥ 5 m · Temp: no floor
Hard ceiling → wind ≥ 28 kt OR swell ≥ 2.5 m = NO, no exceptions
Exception: fully enclosed harbour sites are exempt from the swell ceiling only (ocean swell can't reach them) — the wind ceiling always applies.
McFadyen thresholds (30 years of Sydney field notes)
< 10 kt wind → GO for most ocean shore dives
10–15 kt → caution zone: always MAYBE regardless of other factors
≥ 15 kt → unsuitable for boat & most ocean shore dives
≥ 20 kt → "stay in bed" (McFadyen's exact words)
Shelter / exposure multipliers
Harbour sites (Clifton Gardens, Camp Cove…): swell ×0.03, wind ×0.52
Sheltered-direction sites: swell ×0.32, wind ×0.52
Exposed sites: swell ×1.30, wind ×1.25
Default (semi-exposed): swell ×1.00, wind ×1.00
Swell period multiplier (effective swell height)
Period < 8 s → ×0.80 (short chop, less impact)
Period 8–12 s → ×1.00 (baseline)
Period 12–16 s → ×1.20 (longer groundswell, more surge)
Period > 16 s → ×1.40 (long-period swell, wraps headlands)
🌊 McFadyen Surge-at-Depth Formula
surgeDepth (m) = period² ÷ 4
E.g. a 12-second swell period: 12² ÷ 4 = 36 m. Surge is felt at depths shallower than this figure. Sites where this depth exceeds their max dive depth show a ⚠ surge warning on the card. Source:
michaelmcfadyenscuba.info page 813.
👁 McFadyen Visibility Vocabulary (8-level scale)
| Label | Range |
|---|
| Shithouse | < 2 m |
| Very Poor | 2–4 m |
| Poor | 4–6 m |
| Fair | 7–10 m |
| Good | 10–15 m |
| Very Good | 15–24 m |
| Excellent | 25–30 m |
| Exceptional | > 30 m |
Note: visibility shown in app is inferred from swell/wind, not measured. It's a rough guide. For measured viz before heading out, check Abyss and local dive shop reports.
🤿 Wetsuit Guide (Sydney waters)
| Temp | Suit |
|---|
| > 22°C | 3mm shorty or skin |
| 19–22°C | 3mm full |
| 16–19°C | 5mm full |
| 13–16°C | 7mm full or drysuit |
| < 13°C | Drysuit recommended |
Sydney ranges: ~18–22°C summer, ~16–18°C winter. Cold tolerance varies — these are general guides only.