The Rema in Hilchos Shabbos (end of 262) writes, one should dress himself in Shabbos clothes immediately after washing himself in honor of Shabbos, therefore, to ensure one is able to do the above he should only wash himself close to Shabbos. The Mishnah Berurah (260:4) writes, if one washes himself with hot water on Thursday it is not considered kavod Shabbos, however, if that’s the best one can do then it’s ok, however, the nearer to Shabbos the better. The Aruch HaShulchan (260:6) writes, it’s best to wait until after midday, as it is more recognizable that it is being done in honor of Shabbos. Therefore, when it comes to washing oneself for Shabbos, it is certainly best to wait until erev Shabbos, and not to wash oneself on motzei Tisha B’Av. If one washes himself on motzei Tisha B’Av, it is not really considered kavod Shabbos, since it is not considered kavod Shabbos, it is no different to washing oneself during the Nine Days, therefore, it should be avoided. This is how R’ Shlomah Zalman would pasken (Shalmay Mo’ed 93). Nonetheless, if there is a great need, i.e. one is very uncomfortable, then he may be lenient and wash himself, since strictly speaking according to the Shulchan Aruch, refraining from meat and wine on motzei Tisha B’Av (and the Mishnah Berurah adds washing clothes and washing one’s body) is considered a minhag kosher [good custom], and not a strict obligation.
Even when one washes himself on Friday in honor of Shabbos, he should make sure to only wash himself once, he shouldn’t wash himself on the morning and then a second time in the afternoon. The heter to wash oneself in the morning is because of kavod [honor] Shabbos, if one washes himself again the afternoon, it shows that the first washing wasn’t really for kavod Shabbos.
However, if one is too busy to have a haircut Friday afternoon, and therefore has one on Friday morning, he is allowed to wash himself off from all the hairs, and he may wash himself a second time in the afternoon just before Shabbos (see Netai Gavriel 89:6). Similarly, one who tovel’s [immerses] himself on Friday morning in honor of Shabbos, is allowed to have a shower then, as it is all considered kavod Shabbos.
Being as the entire heter to wash oneself before midday on Friday is due to kavod Shabbos, it’s obvious that it is forbidden to go to the beach on Friday morning, the entire is kavod Shabbos not a blanket heter, and going to the beach is hardly considered kavod Shabbos. However, from midday and on, then strictly speaking it’s ok, however, from the poskim it seems that for a talmid chocham it is fitting to refrain from doing so. The Sha’arei Teshuvah (558:2) quotes from poskim: “G-d fearing Jews are accustomed to be stringent the entire day, so writes the Elyah Rabbah, that from the Bach it seems that one should be stringent the entire day, and so is fitting for a talmid chocham”. Therefore, even though the custom is not to be stringent with the dinim of aveilus after midday, one should refrain from doing positively exciting things, such as going to the beach (see Netei Gavriel 89:13). However, the general practiced custom seems to be lenient in regards to the above.
