Timber Plank (11A21)
This badly eroded timber was found near Fort Bovisand and is unusual as it is covered with small holes on one side. The holes are approximately 5mm square and between 10 to 15mm apart in a semi-random pattern that covers the whole surface. The surface of the holed side has been eroded and attacked by gribble so much of the surface detail is lost while the reverse is much more severely eroded.
The holes show signs of rust and no sign of copper which suggests they were made by iron nails which have long since corroded away. There are no impressions of nail heads on the timber however one nail appears to have been bent over when hit and has left an impression of the side of a nail head that was circular, 10.4mm in diameter and 4.4mm thick. The side of the plank shows a section through nail holes which are tapered and a maximum of 30mm long.
One suggestion is that this is an outer or additional sheathing plank from a ship from below the waterline. The square holes may have been caused by hammering closely spaced iron 'filling nails' onto the outside of the plank which would rust together to form a barrier against attack by shipworm (1,2).
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Images
References
(1) Bingeman J. et al, 2000, Copper and Other Sheathing in the Royal Navy, IJNA 29.2: 218-229
(2) McCarthy M., 2005, Ships' Fastenings From Sewn Boat to Steamship, Texas A&M Press, ISBN 1 58544 451 0, p102