The Hoodwinkers by Monica Edwards.
 
In this new Romney Marsh story Tamzin, Meryon, Rissa, and Roger discover that that whiskery old rogue Jim Decks is once again up to his nefarious activities. And this time he is hoodwinking innocent Americans who, with their love of"history", are convinced that Jim's old boat belonged to William the Conqueror.
 
Jim must obviously be wooed away from these money-making schemes to a more honest line of business. The discovery by Rissa of the drowned village of old Winklesea gives them all an idea. Could not Jim take trippers out to see the ruins charging them so much per head? But how can they afford an engine for the boat? And can Jim be persuaded to adopt the idea? The way to make the money is soon solved and with no lack of adventures. But persuading Jim is another matter; that is until Hookey Galley gets the same idea.
 
Illustrated by Geoffrey Whittam.