Take any Boat NPC, and change the destination co-ordinates.
Or find one of your boat npc's and paste it here, along with your TFS version and someone might edit the script / explain how to do it.
Here's My Npcs XML File
<?xml version="1.0" encoding="UTF-8"?>
<npc name="Captain" script="data/npc/scripts/Captain.lua" walkinterval="2000" floorchange="0">
<health now="100" max="100"/>
<look type="129" head="19" body="69" legs="107" feet="50" addons="0"/>
<voices>
<voice text="I know a secret place hihi" interval2="100" margin="1" yell="no"/>
</voices>
<parameters>
<parameter key="message_farewell" value="Good bye. Recommend us if you were satisfied with our service." />
<parameter key="message_walkaway" value="Good bye. Recommend us if you were satisfied with our service." />
<parameter key="module_keywords" value="1" />
<parameter key="keywords" value="name;" />
<parameter key="keyword_reply1" value="My name is Captain from the Royal Tibia Line." />
<parameter key="keyword_reply2" value="Where do you want to go?" />
<parameter key="keyword_reply3" value="I'm not sailing there. This route is afflicted by a ghost ship! However, I heard that Captain Fearless sails there from Venore." />
<parameter key="message_greet" value="Welcome on board, |PLAYERNAME|. Where may I sail you today?"/>
</parameters>
</npc>
Here's The Lua (The Name Of The Captin In-Game is "Captin" if you want to know that as you can see in this script

local keywordHandler = KeywordHandler:new()
local npcHandler = NpcHandler:new(keywordHandler)
NpcSystem.parseParameters(npcHandler)
-- OTServ event handling functions start
function onCreatureAppear(cid) npcHandler

nCreatureAppear(cid) end
function onCreatureDisappear(cid) npcHandler

nCreatureDisappear(cid) end
function onCreatureSay(cid, type, msg) npcHandler

nCreatureSay(cid, type, msg) end
function onThink() npcHandler

nThink() end
-- OTServ event handling functions end
-- Don't forget npcHandler = npcHandler in the parameters. It is required for all StdModule functions!
local travelNode = keywordHandler:addKeyword({'secret place'}, StdModule.say, {npcHandler = npcHandler, onlyFocus = true, text = 'Psst say secret place please'})
travelNode:addChildKeyword({'yes'}, StdModule.travel, {npcHandler = npcHandler, premium = true, level = 0, cost = 0, destination = {x=1130, y=1245, z=7} })
travelNode:addChildKeyword({'no'}, StdModule.say, {npcHandler = npcHandler, onlyFocus = true, reset = true, text = 'We would like to serve you some time.'})
keywordHandler:addKeyword({'sail'}, StdModule.say, {npcHandler = npcHandler, onlyFocus = true, text = 'Where do you want to go? Secret Place? Or Oken?'})
keywordHandler:addKeyword({'job'}, StdModule.say, {npcHandler = npcHandler, onlyFocus = true, text = 'I am the captain of this ship.'})
keywordHandler:addKeyword({'captain'}, StdModule.say, {npcHandler = npcHandler, onlyFocus = true, text = 'I am the captain of this ship.'})
npcHandler:addModule(FocusModule:new())
The New Hunt Spawn Is Called "Hell" And The Pos Is "32284, 31954, 7" <-- There You Come While Sailing