[Rune Son of Bjarne]

Maybe the Goblins did build the boat, but I doubt it.

First of all it would make more sence for gollum to build it as he could actually need one, I don't see why the Goblins would need it and if they did I think they would build more than one.

Also boat building was never the Goblins strong side, but the riverfolk on the other hand had some skill in this area. So Gollum would probably be better at boat building than the, not that this proves anything at all.

I also think that if the goblins was to explore a lake they would go more than one, at least two goblins would be required and if I remember correctly then Gollum was quite careful when it came to Goblins. I don't think he would dare fighting more than one at the time, even if he did have the ring.