David Calabro suggests (personal communication) that the plural sands here in Alma 2:27 is an error for sand; that is, he proposes that the original text read “the sand of the sea”, not “the sands of the sea” (the reading of the printer’s manuscript). Elsewhere the Book of Mormon text has three other occurrences of “the sand of the sea” but none of “the sands of the sea”:
The last example shows that scribe 2 of 𝓟 (also the scribe in 𝓟 for Alma 2:27) wrote “the sands of the sea”, but in that instance Oliver Cowdery, in his proofing of 𝓟 against 𝓞, corrected the plural sands to the singular sand. Also note that the 1830 edition reads in the singular. For this part of the text (from Helaman 13 through the end of Mormon), the 1830 edition was set from 𝓞, not 𝓟; thus it is probable that 𝓞 read “the sand of the sea” in Mormon 1:7 and that scribe 2 of 𝓟 accidentally wrote the plural “the sands of the sea”, which Oliver corrected to “the sand of the sea”. We should note, however, that here in Alma 2:27 Oliver Cowdery did not correct the plural sands to sand when he proofed 𝓟 against 𝓞. It is therefore possible that 𝓞 itself read in the plural.
Consistent with the singular sand in Isaiah 10:22 (listed above), the current King James Bible has only the singular “the sand of the sea” (nine other times). However, the plural is found in the Apocrypha, which was in the original 1611 King James Bible:
The Apocrypha also has one other occurrence of the singular: “who can number the sand of the sea”, in Ecclesiasticus 1:2.
The plural usage is fairly common in English. Literature Online provides 31 citations of “the sands of the sea”, with dates from 1589 to 1996 (including the one from the 1611 King James Apocrypha). It also provides 24 citations of the singular “the sand of the sea”, dating from the 1611 King James Bible to 1990. This variation argues that either singular sand or plural sands is possible in Alma 2:27. Since the plural usage is possible, the critical text will maintain the single occurrence of “the sands of the sea” in Alma 2:27, even though this plural sands may very well be an error for the singular sand.
Summary: Retain in Alma 2:27 the use of the plural sands in “the sands of the sea”, the reading in 𝓟 and in all the printed editions; this plural reading is possible in English, although the occurrence in Alma 2:27 could be an error for “the sand of the sea”, especially since scribe 2 of 𝓟 seems to have accidentally written “the sands of the sea” in Mormon 1:7.