Lignum vitae was used as bearing material in nuclear submarines as 
recently as the 1970s, end-grain set to rub against steel main drive 
propeller shaft where it runs through the hull, wood blocks adjustable 
as they wear, lubricated by the oils in the wood, and cooled by the 
slight flux of sea water and oily fresh water in and out of the bearing.

I have seen hard maple (sugar maple) knots used as bearing material in a 
late 19th century turbine water power with vertical wooden shaft, wet 
service duty at the bottom of the shaft, within the cast iron turbine 
housing, a knot of wood with a "football" shape was set into the end of 
the shaft, and it fit into a socket made of the same wood set into a 
square socket in the cast iron housing. Location: southern New Hampshire.

John
www.HistoricHomeWorks.com

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