Canon
Canonicamente, não há resposta fornecida nos livros. Ele só tem um barco.
He had a little boat, and he rowed about quite quietly on the lake
The Hobbit: Chapter 5 - Riddles in the Dark
Adivinhação
Gollum fez isso
O Gollum é um Stoor (uma raça de hobbit ou hobbit-like ribeirinhos). Parece que eles são perfeitamente capazes de fabricar seus próprios barcos com materiais frescos.
'Long after, but still very long ago, there lived by the banks of the
Great River on the edge of Wilderland a clever-handed and quiet-footed
little people. I guess they were of hobbit-kind; akin to the fathers
of the fathers of the Stoors, for they loved the River, and often swam
in it, or made little boats of reeds.
Fellowship of the Ring: Chapter 2 - The Shadow of the Past
Gollum roubou
O Grande Duende periodicamente envia seus lacaios para trazer peixes de volta do lago. Uma vez que eles sabem que há água lá embaixo, é difícil imaginar que alguém traria um barco rudimentar com eles, ou os materiais para levantar um deles.
They had come on the lake, when they were tunnelling down long ago,
and they found they could go no further; so there their road ended in
that direction, and there was no reason to go that way-unless the
Great Goblin sent them. Sometimes he took a fancy for fish from the
lake, and sometimes neither goblin nor fish came back.
The Hobbit: Chapter 5 - Riddles in the Dark
Filmes
Na trilogia de filmes de Hobbit, o coracle de Gollum foi construído de peles e ossos de duendes (assim como galhos e pedaços de couro de duende)
Props may often have a reference point in our world while, at the same
time, having some aspect to their design or construction that is
uniquely Middle-earthly. One such example would be Gollum's coracle.
'It is.' says Paul [Tobin], 'a small one-man boat in the ancient style
traditionally used in parts of Wales, Scotland and Ireland. The
significant difference, however, is that Gollum's coracle happens
to made out of the skin and bones of his Goblin victims!'
Limited availability of Goblin body-parts meant that the prop
department had to simulate those gruesome materials as well as making
it possible for Gollum to use it in order to paddle across his
underground lake.
The Hobbit: The Desolation of Smaug Official Movie Guide
e
Gollum’s coracle is made of bits of Goblin skin, bones and a few twigs. He has very limited materials down there so he's made quite a
serviceable little vessel with what he had at hand. It’s unclear in
the book exactly what his boat was made of or how it got there, but
this felt to us like a good, practical alternative to something more
traditional. (Alan Lee: Concept Art Director)
The Hobbit: An Unexpected Journey - Chronicles I: Art & Design***