From what I saw.
The chain was obviously not stacked too well below decks.The man operating the clutch kept backing it off to get the chain to flow.Once it was flowing it was gone and he couldnt brake it.Didnt need to be deep,it would have fed out just as fast in 20m as 2000m deep,the chain is heavy,the anchor or chain length has nothing to do with it;););););)
Andrew

