It’s a common word, but an object to be regarded “with deep misgivings” – and found to have a beautifully uneven distribution. It appears, of course, in chapters where beings and waters interact (5, 8, 9, 10, and 14). Please find the derivatives “Boatmen” and “Boatload” already in the Concordance.

• 5.012 He had a little boat,
• 5.014 Gollum got into his boat
• 5.050 beginning to climb out of his boat
• 5.052 so that Gollum had to get back into his boat
• 5.056 Gollum began to get out of his boat.
• 5.058 This time he did not go back to the boat.
• 5.089 and flapped back to his boat,
• 5.103 in his boat again,
• 5.105 and the splash as Gollum leapt from his boat.
• 8.009 There is a boat against the far bank!
• 8.014 The boat is sure to be tied up,
• 8.016 and see if you can see the boat
• 8.018 and you would have dropped it on to the boat.
• 8.020 It is lying on the boat;
• 8.021 and with a piece of stick fended off the little black boat
• 8.021 in time to seize the boat
• 8.024 That’s as many as the boat will hold at a time.
• 8.027 How are you going to push the boat
• 8.028 and you can draw the boat back.’
• 8.029 in case any hidden guardian of the boat appeared.
• 8.030 thrusting the boat away from the bank,
• 8.030 while the boat span slowly off
• 8.032 and lamenting the loss of the boat
• 9.019 sometimes they were loaded on to flat boats.
• 10.007 and there had been fleets of boats on the waters,
• 10.009 boats rowed out from the piles of the town,
• 10.037 boats
• 10.045 three large boats left Lake-town,
• 14.016 into laden boats
• 14.016 The Master himself was turning to his great gilded boat,
• 14.017 They could all get into boats for all he cared.
• 14.025 Then the many boats could be seen
• 14.025 and most of their boats
• 14.042 He had not boats or rafts enough for his host,

Tolkien, J.R.R.. The Lord of the Rings: One Volume (p. 7). Houghton Mifflin Harcourt. Kindle Edition.