Hand over fist
Quickly and continuously.
This is probably of naval origin. I hesitate to say definitely as the earliest reference to it, although clearly referring to pulling on a rope, doesn't explicitly mention ships.
The allusion in this phrase is to the action of hauling on a rope. An earlier version of the phrase was 'hand over hand', which dates to the mid 18th century. This is found in a paper by Cooke in the Royal Society's Philosophical Transactions for 1736:
"A lusty young Man attempted to go down (hand over hand, as the Workmen call it) by means of a single Rope."
Not longer after that William Falconer's An universal dictionary of the marine, 1769 has this entry:
"Main avant, the order to pull on a rope hand-over-hand."
The term is now used to suggest speed and profusion, especially in financial dealing, e.g. 'making money, hand over fist'. In the 18th century 'hand over hand' and the later 'hand over fist' had a different meaning though and meant 'making steady progress'. 'Hand over fist' is a little more descriptive of hauling on a rope than 'hand over hand', after all, when we grab on a rope to pull it we do make a fist and then reach forward with our other open hand. This term makes an appearance in William Glascock's The naval sketchbook, 1825:
"The French ... weathered our wake, coming up with us, ‘hand over fist’, in three divisions."
Many of the early citations refer to slow steady progress - exactly what could be expected if a ship were being pulled closer to another by means of a rope.
The 'making money hand over fist' figurative use is a clear allusion to grabbing handfuls of money and pocketing it. This is later, but not much later, in Seba Smith's The life and writings of Major Jack Downing, 1833:
"They... clawed the money off of his table, hand over fist."
See other Nautical Phrases.