> The pass is 500 metres (1,600 ft) across, but the main navigation channel (the "throat" or "narrows") contracts down to only 100 metres (330 ft) with a 20-metre (66 ft) deep shoaling region. Most of the rest of the pass is broken reef.[8]
> On one side is Cook Strait with a tidal range up to 2 metres (6.6 ft), and on the other side is Tasman Bay with a tidal range up to 4 metres (13 ft).[9] This can result in substantial pressure gradients across the pass, complicated by a phase or time difference of about 25 minutes between the high tides on either side. Peak flow in the throat of the pass is around 4 metres per second (13 ft/s).[10]
> Near to the pass are deep holes where strong vertical flows can occur.[11] In 2000, student divers taking part in a drift dive during the local ebb flow were separated from their surface float and caught in a whirlpool. This dragged them into "Jacob's Hole", a 68-metre (223 ft)[12] deep depression south west of the pass. The depth of this descent resulted in multiple fatalities. The group appears to have been drawn deep into the hole and then returned to the surface again. A dive computer record of one of the survivors show a depth of up to 89-metre (292 ft). According to the coroner's report, the accident occurred on a falling tide, so the current was flowing from the south west to the north east.[13][14]
https://en.wikipedia.org/wiki/Te_Aumiti_/_French_Pass
> The pass is 500 metres (1,600 ft) across, but the main navigation channel (the "throat" or "narrows") contracts down to only 100 metres (330 ft) with a 20-metre (66 ft) deep shoaling region. Most of the rest of the pass is broken reef.[8]
> On one side is Cook Strait with a tidal range up to 2 metres (6.6 ft), and on the other side is Tasman Bay with a tidal range up to 4 metres (13 ft).[9] This can result in substantial pressure gradients across the pass, complicated by a phase or time difference of about 25 minutes between the high tides on either side. Peak flow in the throat of the pass is around 4 metres per second (13 ft/s).[10]
> Near to the pass are deep holes where strong vertical flows can occur.[11] In 2000, student divers taking part in a drift dive during the local ebb flow were separated from their surface float and caught in a whirlpool. This dragged them into "Jacob's Hole", a 68-metre (223 ft)[12] deep depression south west of the pass. The depth of this descent resulted in multiple fatalities. The group appears to have been drawn deep into the hole and then returned to the surface again. A dive computer record of one of the survivors show a depth of up to 89-metre (292 ft). According to the coroner's report, the accident occurred on a falling tide, so the current was flowing from the south west to the north east.[13][14]