Dive 2 — The Survey Ring (First Hexagon)

Safety and gas bind before the survey does. Adapt to the conditions or stop — a partial ring is always a valid outcome.

Dive 2 is the first complete survey. The camera enters the water for the first time, and the team runs the full six-station ring around a fixed hub, producing the dive's first density reading. The calibration from Dive 1 — the kick count K and the visibility r — is carried in on the slate, and the survey geometry (R = 2r, the six stations, the heading table) was computed dry in the planning session between the dives. Nothing is measured here that was not already established; Dive 2 executes the plan.

The pattern, in one line. 2r kicks, add 60°, six pictures — the rule the diver carries, developed in Module 4. From the hub the legs run:

Leg Compass Distance Arrive at

out from hub 000° 2r kicks center 1

1 → 2 120° 2r kicks center 2

2 → 3 180° 2r kicks center 3

3 → 4 240° 2r kicks center 4

4 → 5 300° 2r kicks center 5

5 → 6 000° 2r kicks center 6

6 → 1 060° 2r kicks back at center 1 — ring closed

A 360° panorama is taken at each of the six centers. The stop rule is six pictures, not a compass reading: note that 000° appears twice (the leg out and the leg 5 → 6), so "stop when the compass reads north" is ambiguous, while counting six captures is not. Arriving back at center 1 on the closing 060° leg confirms the ring is shut.

Performance requirements. By the end of this dive the student will have:

1. Carried the calibration (K, r) and the computed geometry (R = 2r, the heading table) into the water correctly.

2. Run the complete six-station ring from a fixed hub and a fixed north: out 2r on 000°, then five legs of 2r at +60° increments, a panorama at each of the six centers, closing the ring. (Six stations, six captures. Counting the initial swim-out and the closing leg back to the first center, that is seven legs swum in all — but the count that governs the dive is pictures, and it is six.)

3. Operated the 360° camera at each station from a stable, neutral, no-contact position.

4. Worked the two-observer protocol — one diver as photographer and station-keeper, the other as recorder — producing a reconcilable count.

5. Counted only reef-associated organisms, and held buoyancy and no-contact throughout.

Equipment for this dive. Standard scuba kit with a nitrox computer set to the analyzed mix; the 360° (full-surround) camera; a compass; the survey slate carrying K, r, and the heading table. No reel or guide line.

Pre-dive briefing. Confirm the hub (the reference point), how north is set, and that it must be the same north for all six legs. Confirm the gas plan and the gas-limited turn-around, and the no-reel, no-contact discipline. The ring pattern, the two-observer roles, and the counted set are executed as stated in the performance requirements (Modules 4–6).

The dive.

1. Descend to the hub; establish neutral buoyancy and horizontal trim; set and confirm north.

2. Leg out. On 000°, swim 2r kicks to center 1.

3. Capture. From a stable, no-contact position, take the 360° panorama. The recorder notes the station and the in-water count of reef-associated organisms.

4. Walk the ring. Add 60° to the compass (120°), swim 2r kicks to center 2, capture. Repeat — 180°, 240°, 300°, 000° — a panorama at each center, until six captures are made.

5. The closing leg (060°) returns the team to center 1, confirming the ring is shut.

6. Ascend with a safety stop.

Post-dive. Offload the six panoramas. The recorder's in-water tally and the post-dive image count are compared at each station; their disagreement is the counting error for the dive (Appendix A.5). Each station's count is divided by the area its capture saw, giving that station's density; the dive's site index is the average of the six station densities — the densities are averaged, never the counts pooled over a summed area. The calculator does this arithmetic from the slate (Section Four); the formulas are in Appendix A.3 and A.7. Debrief the navigation (did the ring close within tolerance?), the count reconciliation, buoyancy, and no-contact.

Assessment. The dive is satisfactory when the student has run the complete six-station ring from a fixed hub and north, operated the camera from stable no-contact positions at all six centers, produced a reconcilable two-observer count of reef-associated organisms, and computed (topside) the six densities and their average. Navigation that fails to close the ring within a reasonable tolerance, or counts that cannot be reconciled, are remediated before Dive 3.

Depth range. 6–18 m, at a depth representative of the survey, consistent with the gas plan (gas and no-decompression time both hard limits, either reached first).