Sentence:  He and Gerald usually challenged the rollers in a sponson <WSD>canoe</WSD> when Gerald was there for the weekend; or, when Lansing came down, the two took long swims seaward or cruised about in Gerald's dory, clad in their swimming-suits; and Selwyn's youth became renewed in a manner almost ridiculous,nb.... 
Meaning of the word marked with <WSD> tags:  A small long and narrow boat, propelled by one or more people (depending on the size of canoe), using single-bladed paddles. The paddlers face in the direction of travel, in either a seated position, or kneeling on the bottom of the boat. Canoes are open on top, and pointed at both ends.