Andrew Mclean, curator for the National Trust, said: “It is fabulous that new material relating to the Delaval family is still coming to light as we are always interested in finding out more about the family.
“Admiral Delaval was an important naval figure so anything that relates to his career at sea is fascinating.”
Caroline Hodges, a director of Boldon Auction Galleries, said: “The documents give a real insight into historic naval warfare.
“The document asking for details of stocks and consumption of food and other goods by the ships is like a very basic spreadsheet to be filled in and sent back.
“In the days before modern communications they had to rely on these letters gong back and forth. They give a picture of everyday life and how they went about their business on board ship.
“We hope that the documents stay in the North East.”
GEORGE Delaval was a Navy captain in 1695 and also served as an envoy to Morocco and Portugal.
In 1718 he was promoted to the rank of rear admiral and served on the Royal Oak.
In the same year he wrote to his brother: “I intend to persuade Sir John Vanbrugh to see Seaton and to give me a plan of a house or to alter the old one.”
The decision was taken to demolish the old house and build the mansion which stands today.
In 1720, a total of 220 men were employed on the project.
But George did not live to enjoy his palatial new home. In 1723 he died after a fall from his horse.
Whatever you need this Christmas, go to www.LocalMole.co.uk - the fast, accurate local business directory.