The wikipedia article for bowline gives two pronunciations /boʊlɪn/ or /boʊlaɪn/.
The history section says:
The bowline's name has an earlier meaning, dating to the age of sail.
On a square-rigged ship, a bowline (sometimes spelled as two words,
bow line) is a rope that holds the edge of a square sail towards the
bow of the ship and into the wind, preventing it from being taken
aback.
This is what I was expecting; yet, we pronounce it as /boʊ/ not /baʊ/.
The same section goes on to say:
The bowline knot is thought to have been first mentioned in John
Smith's 1691 work A Sea Grammar under the name Boling knot.
What does "Boling" refer to? How is it pronounced?
If it is pronounced /boʊlɪŋ/ then I can imagine the 'g' being dropped in usage,
producing /boʊlɪn/, which was somehow applied to the spelling "bowline".
When and why did /boʊlaɪn/ (as opposed to /baʊlaɪn/) become a coherent pronunciation?
— IPA —
/ɪ/ = i in pit
/аɪ/ = i in ride
/aʊ/ = ow in how
/oʊ/ = o in joke
Best Answer
John Smith, 'boling', and the 'boling knot'
The term Boling knot appears in John Smith, A Sea Grammar: With the Plaine Exposition of Smiths Accidence for young Sea-men, enlarged, published not in 1691 (as the Wikipedia article on bowline erroneously states) but in 1627. Here is the relevant paragraph from Smith's Grammar:
Elsewhere in the same chapter of the Grammar (titled "How all the Tackling and Rigging of a Ship is made fast one to another, with their names, and the reasons of their use"), Smith discusses the function of the boling itself:
This John Smith is most familiar to people today as the Englishman in the Pocahontas story. Smith uses the word line in the sense of "rope" multiple times in the course of the Grammar, and he identifies certain specific types of rigging in compounds that use that spelling: leech lines, Knave- line, smiting line, clew line, rayling lines, Dipsie line, Log line, Sounding line. The three exceptions to this usual pattern are boling, ratling ("all those small ropes doe crosse the Shrouds like steps are called Ratlings"), and marling ("Marling is a small line of untwisted hemp, very pliant and well tarred, to sease the ends of ropes raveling out, or on the sides of the blockes at their arses").
As for bow, Smith spells that word in his Grammar as you'd expect him to when it stands alone, as in the chapter on ship building:
Of course, this spelling provides no clear indication as to whether the normal pronunciation of bow in Smith's time rhymed with "how" or with "low."
If a bowline is (as Merriam-Webster's Eleventh Collegiate Dictionary reports) "a rope used to keep the weather edge of a square sail taut forward"—that is, toward the bow—there is little reason for Smith to have preferred the spelling boling over bow line unless (in 1627) "boling" closely approximated the standard sea-man's pronunciation of the term at that time. This in turn would suggest that the pronunciation 'bō-lən (to use Merriam-Webster's system of pronunciation symbols), which the Eleventh Collegiate gives as the more common pronunciation of bowline today ('bō-'līn is the only other named variant) was already very nearly in place in English speech in 1627.
Other early matches for 'boling', 'bow-line', and 'bowline'
Boling also appears (and bowline does not) in Elisha Coles, An English Dictionary: Explaining the Difficult Terms that are used in Divinity, Husbandry, Physick, Philosophy, Law, Navigation, Mathematicks, and Other Arts and Sciences (1676):
This same entry, with minor changes in capitalization, also appears in editions of Coles as late as 1732.
Nathaniel Bailey, Dictionarium Britannicum: Or a More Compleat Universal Etymological English Dictionary (1730), however, lists two spellings—bow-line and bowling:
However, Bailey's An Universal Etymological English Dictionary, second edition (1731) drops the entries for bowline/bowling and for bowling knot, and retains only a brief three-part entry for check the bowline, ease the bowline, and run up the bowline, defined as "{Sea terms} which import, let it be more slack."
The earliest match for the spelling "bowline knot" is from Daniel Baron Lescallier, Vocabulaire des termes de marine anglois et françois (1777), a French-English dictionary of nautical terms:
But an English-Swedish dictionary from 20 years early has no compunction about switching from bowline to boling-knot in the same block of phrase translations. From Jacob Serenius, An English and Swedish Dictionary (1757):
Even earlier, Daniel Defoe, in Letter 53 of Miscellany Letters: Selected out of Mist's Weekly Journal (1722) opens one with the salutation "Mist, you Haul-Bowline Dog..."
William Falconer, An Universal Dictionary of the Marine (1784) has multiple instances of bowline, including this entry for the term: