Taffrail

A Taffrail is the aftermost railing around the stern of a ship, often, but not always, ornately carved. A taffrail log is an object dragged from the stern of the vessel to calculate the vessel's speed through the water.

External references

[http://www.chantryisland.com/nautical_terms.htm Nautical terms]
[http://www.penobscotbayhistory.org/glossary_popup/show/733 Penobscot Bay history site] on taffrail log
[http://americanhistory.si.edu/collections/navigation/object.cfm?recordnumber=859451 Information about John Bliss and Co. taffrail log] (1867)