Short answers, pulled from the story.
Wat Yannawa is called the boat temple because King Rama III ordered a viharn built in the shape of a Chinese junk during his reign. The two chedis on the deck represent masts, and the altar at the back represents the wheelhouse. The Thai name Wat Yannawa itself translates as the boat temple.
King Rama III built the junk-shaped viharn because he believed the Chinese junk was becoming obsolete due to new ship types arriving in Bangkok. He chose this form as a means of historical preservation, wanting to fix the image of the junk permanently in stone at a site that would be visited and tended across generations.
Wat Yannawa is located on Charoen Krung Road in the Sathon district of Bangkok, Thailand.
The temple was originally called Wat Kok Khwai, a name that referenced the community of Dawei people in the area who bought and sold buffalo. It was later renamed Wat Kok Krabue before receiving its current name, Wat Yannawa, during the reign of King Rama III.
The stern of the junk-shaped viharn enshrines four Buddha statues and replica footprints with Thai and Chinese inscriptions. The two chedis that serve as masts differ in size: the larger has 20 wooden recesses and the smaller has 16. A room within the structure holds relics believed by some to come from Buddha.
A building on the exterior grounds of Wat Yannawa enshrines a Buddha relic from Sri Lanka. The temple also houses three statues of the Goddess of Mercy in a separate Chinese-style building on the grounds.