Question: May one wind up a mechanical watch on Shabbat which works on a spring mechanism in order for it to continue working?
Answer: This question can actually be divided into two separate issues: Firstly, is it permissible to wind up a watch which is currently not working at all? Furthermore, is it permissible to wind up a mechanical watch that is currently working but must be wound up in order for it to continue operating?
Winding Up the Spring of a Watch that is Not Working
Let us first discuss the law regarding winding up a watch that is currently not working. This would seem to be prohibited, for one of the forbidden works on Shabbat is “repairing a vessel.” Thus, winding up the spring of the watch is its repair, for immediately upon doing so, the watch will begin to work.
Indeed, we find in Rashi’s commentary on Masechet Eruvin (103a) that if one of a violin’s cords became loose (and cannot be used to play the instrument) and the musician turns the knob of the violin in order to tighten the cord, this constitutes the prohibition of “repairing a vessel” on Shabbat, which is a Torah prohibition. It would seem that the same would apply to winding up the spring of a watch, for by “tightening” it, it becomes operational and thus, one who does so has repaired a vessel on Shabbat. Indeed, several Acharonim rule that there is an absolute prohibition to wind up a watch on Shabbat based on the aforementioned words of Rashi.
Maran Rabbeinu Ovadia Yosef zt”l rebuffs this claim (in his Responsa Yabia Omer, Volume 6) because there is a distinction between the two cases, as follows: Regarding the violin, when its cord becomes loose, the violin is broken and repairing it requires tightening the cord. Thus, such a repair constitutes Shabbat desecration. On the other hand, regarding the watch, even without the spring being wound up, the watch is in working order and not in a state of disrepair whatsoever; thus, winding it up does not create an action worthy of being classified as a “repair”. Nevertheless, Maran zt”l concludes by ruling stringently and that one should not wind up a watch that is currently not working on Shabbat, for there is still a concern of repairing a vessel on Shabbat.
Summary: One may not wind up the spring of a mechanical watch which is currently not working on Shabbat. In the following Halacha, we shall discuss more details regarding this law.