Wiktionary
clap on
vb. (context nautical transitive English) to temporarily add something to an existing part, especially to add an additional sail to take advantage of a fair wind
WordNet
Usage examples of "clap on".
I bade him good morning, standing to leeward of him on the quarter-deck, and he saluted me with a clap on the back.
While Jack was struggling with his duties as a host and adjuring the steward 'to clap on to its beakhead' and 'to look alive', James turned to Stephen with a fellow-guest's smile and said, 'Is it not possible that I have already had the pleasure of being in your company, sir?