I believe what you are thinking about is known as a shroud needle
pic here about 3/4 of the way down the page
http://www.hurstwic.org/history/arti...orse_ships.htm
I'm sure i have a more detailed pic in a book somewhere, just finding it is a bit of a challenge
p.s you could try contacting these people
http://www.vikingeskibsmuseet.dk/index.php?id=1246&L=1 I remember hearing something about them having problems with the shroud needles breaking on one of their replicas, Sea Stallion