The Gemara in Berachos (24b) teaches: היתה טליתו חגורה על מתניו מותר לקרות שמע – “one who has a garment covering himself from waist down, may recite krias shema”. Rashi explains, as long as one is covered from waist and down, even if his top half is naked, he may recite krias shema. The Gemara continues, that when it comes to tefillah one has to cover his heart as well. Rashi explains, when one davens he has to dress as if he is standing in front of a king, and stand in fear etc., however, for krias shema one doesn’t.
L’halachah the Rambam (Hilchos Tefillah 4:7) writes:כיסוי הערוה כיצד אע"פ שכסה ערותו כדרך שמכסין לק "ש לא יתפלל עד שיכסה את לבו ואם לא כסה לבו או שנאנס ואין לו במה יכסה הואיל וכסה ערותו והתפלל יצא ולכתחילה לא יעשה – “How does one cover his ervah? Even if one covers himself the way one covers himself for krias shema, he shouldn’t daven shemonah esrei until he covers his heart. If he doesn’t, or he is in situation where he can’t, as long as he covered his main ervah (from the waist down) and davened, he fulfills his duty, however, ideally one shouldn’t do this.”
The end of the Rambam, ולכתחילה לא יעשה – “ideally one shouldn’t do this” is very difficult, as the Rambam already said: לא יתפלל עד שיכסה את לבו – “he shouldn’t daven shemonah esrei until he covers his heart”, so what is he adding?
The Biur Halachah (91:1 d.h. yotsa) explains, that the Rambam is teaching us that if one is in a situation where he doesn’t have what he needs to cover himself, it’s better that he doesn’t daven at all. R’ Chaim Kanievsky (Ishei Yisroel 10:9) adds, that this applies even if one will end up missing sof zman tefillah. By krias shema there is a heter to read it, if one covers himself from waist down, however, when it comes to tefillah there is no heter, and one has to cover his heart, if he can’t, he should refrain from davening. However, the Aruch HaShulchan (91:4) argues on the Biur Halachah and maintains, that under pressing circumstances one may daven shemonah esrei without covering his heart. This is also how the Kaf HaChaim rules, although he adds, if he can easily get hold of clothes he should.
The above is in regards to shema and shemonah esrei, the question is, if birchas hanenin is similar to shema or shemonah esrei: if it’s like shema then even if one is only wearing swimming trunks it would be ok, if however, it is similar to shemonah esrei then according to the Biur Halachah it would be a problem.
The Shulchan Aruch (206:3) in regards to birchas hanenin rules, that one shouldn’t make a berachah unclothed, and one must cover his ervah. However, it’s not clear if it helps to be covered from waist down, or if one has cover his heart as well. However, in Hilchos Krias Shema where the Shulchan Aruch rules that for shema it’s ok to be covered from waist down, the Mishnah Berurah comments that the above is only under pressing circumstances, however, ideally for shema and all berachos one shouldn’t. From the Mishnah Berurah it’s clear, that when it comes to reciting berachos, one should ideally cover his heart as well.
Halachah lemaseh, one should certainly try to cover himself, from waist and up when reciting a berachah. In regards as to exactly how much one needs to cover, there is a Tevuas Shor (1:38) in regard to Hilchos Shechitah who writes that one should cover himself from “his heart until his neck”, however, the poskim don’t bring this. However, certainly, one should either cover himself with a towel or put on a top before making a berachah. This is how R’ Elyashiv would pasken (see V’Zois HaBerachah 1:4).
In regard to birchas hamazon, R’ Shlomah Zalman Auerbach (Halichos Shlomah, Perek 2, He’orah 73) that one shouldn’t say it whilst only wearing swimming trunks, and one should either cover himself properly, or get dressed first, as birchas hamazon is similar to shemonah esrei (as is clear from Orach Chaim 183:8).
