Is one allowed to set up a hammock on Shabbat? Like hanging up a hammock between trees, poles etc.? In this case the hammock is temporary to be slept in/used over Shabbat but will be taken down after Shabbat. If it’s temporary, is it still considered Boneh if it’s simply being attached?
Refer to Shemiras Shabbos Kehilchasa 16:16
(Feldheim version, Vol. 1 pp.191-192)
a. One is allowed to rock on a swing or in a hammock, as long as it is not fixed to a tree, even on one side.
b. 1) One is allowed to use a swing or hammock hung from a pole or bar between two trees, provided that
a) the swing or hammock was in place before Shabbos or Yom Tov and
b) the trees are firm enough not to sway with the rocking motion.
The reason is that in this case no direct use is being made of the trees, since the swing or hammock is not attached to them, but rather to the pole or bar, which, in turn, is attached to the trees.
It is forbidden to attach the swing or hammock to the pole or bar on Shabbos or Yom Tov.
Also refer to Rabbi Dovid Ribiat's The 39 Melochos - Vol. 2, p.294:
Rabbinical restriction of Kotzair [reaping]
A number of activites were Rabbinically restricted because they could lead inadvertently to the Melocho of Kotzair, including the following restrictions:
- Use of a tree (e.g. climbing a tree, tree swings, hammocks etc.)
- Smelling fruits attached to a tree
- Handling and eating fruits from a tree on Shabbos.
a) Using a tree (משתמש באילן) It is forbidden to use a tree on Shabbos and Yom Tov. "Use" un this Halachic context means, among other things, climbing a tree, leaning against a tree, or sitting on it.
The Sages prohibited using a tree on Shabbos because this type of activity is likely to lead to the transgression of Kotzair. This restricted activity is known as משתמש באילן (Mishtameish B'ilan). A person climbing a tree, or swinging and leaning on a tree is prone to inadvertently detach part of the tree, e.g.. breaking off some bark or a branch or twig etc. The Sages therefore imposed a form of Muktza status upon the trees.
The usage of any part of the tree is forbidden, including branches and exposed roots (that are above 3 Tefochim - approximately 12 inches - from the earth). The restrictions on usage of trees includes the following:
- Climbing a tree
- Leaning against a tree
- Shaking a tree
- Placing objects upon a tree
- Removing objects form a tree (e.g. dislodging a ball from bushes)
Tree swings and hammocks that are fastened directly to a tree are also considered as using the tree.
Merely touching a tree, however, is not classified Halachically as use, and is permitted, as long as doing so does not cause the tree to move or shake at all.