(grin) first of all the Boatman is Domaphles, no a, less you offend one who is alot more noble.
Point 2 - he only offers to ferry you to the island. If you paid attention, he said he would leave at first light or something like that.
Point 3 - He never promised you a Rose Garden or getting into the protected walls of Allesandra. Once on the island you must solve the next puzzle yourself. Something to do with a triangle perhaps?
Finally, if you get there, then must get home on your own. Skyflight works if you have the skill and a mount :)
Written by my hand on the 15th of Midwinter, in the year 1127.