Greetings once again from a very hot south Florida,
In eruvin 43 the Gemorah presented the question whether techum has a ceiling of ten tefachim or not. One of the nafka minas is by the case of the boat. If techum does have a ceiling then the members of the boat did not establish ther residence on the outset of shabbos being that they were ten tefachim over the floor of the ocean.
A member of the daf asked the following question. Earlier we saw that Rava maintains that the place in which a person is making his place of residence has a quasi- reshus hayachid status associated with that area, in that his makom sh'visah goes up ad-infinitum like a reshus hayachid. Would it then not follow that it would also go down infinitely like a reshus hayachid so that even if techum does have a ceiling, a person's makom sh'visah would go down into the techum to create his residence?
again, thank you for the wonderful work.
(a) We find, however, that Rashi (33a, DH v'Hu Niskaven) implies that we make the area above ten Tefachim into a Reshus ha'Yachid only l'Hakel , where doing so would be a leniency, so that his Eruv will take effect when he placed it in Reshus ha'Yachid, but not l'Hachmir.