The Oxford English Dictionary (OED) calls "yaugh" and "yaught" obsolete forms of "yacht." That dictionary's entry for "yacht" includes these quotations:
"1616 R. COCKS Diary (Hakl. Soc.) I. 118, I esteemed he came to spie..whether our shipp and the Duch yaught staid for to take the Amacon shipp. ... 1630 R. Johnson's Kingd. & Commw. 40 The Emperour (who yet had never greater vessell than a Punt or Yaugh upon the Danuby). 1645 in Sussex Archæol. Coll. XLVIII. 129 Paid for tow and nails used aboute my Lords Yought at Pemsie. Ibid., To unrig my Lord's Yaught."