DOUBLE ENTENDRE
She [the boat] has a bluff bow, lovely lines.
Bow - (5th definition) - noun - the front part of a ship.
Bluff - (1st definition) - having a broad and flattened front.
Here we have a literal interpretation:
The boat has a broad and flattened front and has a nice shape.
She [a woman] has a bluff bow, lovely lines.
Bluff - (1st definition) - adjective - having a very open, honest, and direct way of talking that is friendly but not always polite.
1a. a broad and flattened front
Bow - (1st definition) - intransitive verb - to bend the head, knee, body in reverence
Consider the 3rd and 4th definitions as well to see the many forms of BLUFF and bluffing
Here we have a metaphorical interpretation:
She bends her body to show respect rather quickly and freindly but maybe deceptively, she also has (lovely lines) a beautiful body.
Because of the boat being referred to as a she, combined with the fact bow has two seperate meanings for a boat and a woman, the author has created a double entendre.
This is done by a writer exploiting ambiguity and puns.
Per the arguments below I have cleaned my answer up to make the poetics more apparent. I sometimes write quickly and fail to consider that not everyone is of the same reading capability or I may sometimes be ambiguous unintentionally.
At most, you could say that the author did not intend to do this. Which would make it out of context in relation to the authors desire of meaning. However, I think the author intended to mean this as a way to embellish HER.
SHE IS A DEADLY, DECEPTIVE, GRACEFUL, BEAUTIFUL THING.
Morever, both contructions follow pragmatic rules of literature.
Although there are no specific instances of 'bluff bow' [adj + verb] there are instances of other [bluff+verb] formations as well as many other [adj + verb] formations. Which concludes this formation is acceptable at least colloquially.
bluff run - 1) used to signify a practice race or 2) a sample test
- "Are you going to participate in the 5K bluff run?"
- "We are going to conduct a bluff run on the fire alarm"
It's up to YOU to decide what you think the author's intentions are.
Resources from Merriam-Webster and Google Ngram