One Tree Island - Operational Considerations for Boating and Diving

Weather

Weather forecasts are available daily from station managers. With respect to diving operations, the Dive Coordinator must satisfy him/herself that the weather and sea conditions at the proposed site(s) will not compromise the safety of any personnel. However, the Station Manager has the final say as to whether boating (and thus diving) activities are permitted in marginal or rough weather/sea conditions.

Tides and currents

The tidal range around One Tree Island can be up to 3.5 metres and strong currents are associated with these spring tides.

Tide tables for One Tree Island are available from the station managers, and shall be consulted prior to any diving or boating operations taking place.

Divers, Snorkellers and Boat Operators must always check the current strength and direction before entering the water, and anticipate any increase in current flow or change in direction.

Dive coordinators and leaders must be aware of precautions that must be exercised with regard to currents. Prior to entering the water the Dive Coordinator, Dive Attendant / Boat Person and dive team must discuss the rescue procedures to be followed; should one or more divers be caught in a current whilst other divers are still underwater / on-site:

  • Diving in currents stronger than a diver can easily swim against is strongly discouraged.
  • All divers involved in diving in strong currents must be experienced in this type of diving and be tethered to the boat or use a surface float so their location is always visible.
  • An experienced boat handler with knowledge of local conditions must be in charge of the vessel.
  • Where an anchored vessel is being used for untethered SCUBA operations in strong currents, a float line must be used by all divers and a current line of at least 30 metres length and 10mm diameter must be streamed behind the vessel.
  • The divers must only work 'up-current' of the vessel, and must remain in buddy contact.
  • It is strongly recommended that divers descend and ascend along the anchor line.

A diver on the surface caught in a current downstream of the dive boat's current line, should remain calm, and fully inflate their BCD and their surface signalling device. A whistle should also be used to attract the Dive Attendant's attention.

Diving in currents demands an extra level of fitness and divers must pay particular attention to their air supply, as air consumption can be dramatically increased due to the extra exertion involved in diving in currents.

Operational cut-off limits for diving from a marine vessel

  • Boats less than 6 metres length: Diving on the windward reef edge when wind speeds are in excess of 15 knots and/or significant wave height is in excess of 1.5 metres should not be undertaken.
  • Boats 6 metres in length or greater: Diving on the windward reef edge when wind speeds are in excess of 20 knots and/or significant wave height is in excess of 2.0 metres should not be undertaken.

Boating (and thus diving) outside the reef crest during a Strong Wind Warning is at the manager's discretion. As per the University of Sydney Diving Operations Manual, weather and sea conditions must be evaluated by the Dive Coordinator and discussed with all divers. Attention should be paid to weather and sea conditions beyond the sheltered areas of the reef, such that in the event of a rescue or search operation being required to be conducted at sea, i.e. away from sheltered conditions, it would not impose unsafe conditions for any persons or vessels involved.

No diving operations are to take place outside the reef crest during a Gale Warning issued by the Bureau of Meteorology.

No diving is to take place outside of the lagoon system when surface visibility is less than 100 metres.

Vessels must be anchored safely and securely. Immediately upon entering the water divers must check that the anchor will hold securely for the duration of their dive, and that no parts of the anchor rope will become damaged by chaffing on coral or reef (consideration must be given here to the fact that conditions, such as tidal currents and wind speed / direction may change throughout a dive, i.e. a boat's position may shift through 180 degrees in a short period of time).

Underwater visibility

Underwater visibility in the lagoons and around the outer reef edge may be dramatically reduced with ebbing tides, to less than 2 metres. This should be considered before every dive. Measures should be considered and taken if necessary, prior to any dive, which may assist divers to operate in poor visibility.