First of all; while present Czechia is landlocked and the Kingdom of Bohemia was also landlocked for most years of its existence, Czechs are no strangers to seafaring.
Probably the most famous Czech in this regard was Augustine Herman, born around 1620. He was a businessman, an outstanding cartographer, a corsair sailing the ship "La Grace" and later a member of the advisory board of the director-general of New Amsterdam (present day New York).
Another one was Kryštof Harant of Polžice and Bezdružice, born in 1564. A noble, a diplomat, a warrior, a writer, a traveller. He sailed around the eastern half of the Mediterranean Sea and wrote a book about his adventures called "Journey from Bohemia to the Holy Land, by way of Venice and the Sea".
There were countless Czechs joining naval crews in search for a new home during the 30-Year War when they were forced to either convert to catholicism or to go into exile.
There are several theories of what is the etymology of the term and how the greeting found its way into present day Czech.
I would be sceptical about this explanation. I couldn't find any proof about this version. Neither it is clear from these rumours whether Igor simply used the English word "ahoy" or if it was a Czech term, eg. "hou" used in Czech to herd cattle.
An abbreviation of the latin phrase "Ad HOnorem Iesu", which means "For the honour of Jesus". The abbreviation AHOI might have changed to AHOJ over time since Jesus is called "Ježíš" in Czech. It doesn't make much sense for English though since the English word "ahoy" doesn't match any transcription of Jesus' name. There is also little probability that common sailors in 17th/18th century would greet themselves with an abbreviation. Therefore it doesn't seem that the Czech word "ahoj" was born this way.
The most likely origin is this one: The English term "a hoy" which evolved into the greeting "ahoy" was brought to Bohemia through German rivers where freighter crews and other ship travellers would meet and spread the greeting. Another helping factor would also be the rise of walking tourism and canoe/paddling tourism in late 19th and early 20th century in these regions.
Probably the oldest written proof of origin is in the Otto's encyclopedia from 1888 which still uses the archaic form "ahoi" and relates the term to interaction of officers and crews on warships. It also defines the term as a naval greeting and a rower club greeting. The text fragment in Czech is here:
"Ahoi (ohoe), heslo užívané na válečných lodích asi v tom smyslu jako u vojska pozemního volání „Kdo tu?“ Stráž na lodi oslovuje v noci každý blížící se člun voláním: „Člun ahoi!“, načež řídič člunu musí odpověděti, koho k lodi přiváží. V kterém člunu mimo posádku nikoho není, ten hlásí v odpověď: „Na palubu!“; v kterém jsou důstojníci, ten odpovídá podlé toho, jakou hodnost zaujímají, voláním: „Důstojníci )!“ – Štáb!“ (náčelnictvo) – „ Komodor!“ – „Admirál!“ Přiváží-li se člunem velitel, hlásí se jménem lodi, které velí. Řidič osloveného člunu, který k lodi nehodlá přistati, volá v odpověď: „Dále!“– Ahoi užívá se též jako pozdravu námořního a zejména jako hesla veslařských spolků."
In any case, we do know that around 1920 canoe tourism in Czech part of Czechoslovakia was already widely popular and the term "ahoj" already widespread among paddlers.
It is worth mentioning that followers of tramping and canoe riding back then were a specific social group dreaming of faraway lands, seas, the Wild West, etc. and generally seeking romance in the countryside. "Ahoj" was their trademark greeting and while they valued considerate treatment of nature, they haven't necessarily valued other "high" ideals of other social groups like Sokol members (the Czech equivalent of the nowadays Scout organisation). Sokols had/have their own official greeting "Nazdar!", which can be translated as "Let us succeed!".
Another note can be found in the Pocket Vocabulary of the Czech Language, edition 1935-1937; the word is already established in the form "ahoj" and is defined as a greeting of sailors, ship crews, scouts and as an encouraging interjection.
The socialism era of 1948-1989 in Czechoslovakia brought suppression of the Sokol organisation along with its greeting "Nazdar!" while the government tried to promote the communist greeting "Čest práci!", which means "Labour be honoured!". The government didn't mind if people used "ahoj" because unlike Sokols, tramps and canoeists weren't (open) enemies of the regime (if anything, they wanted to escape the oppression of city-based institutions). Therefore, "ahoj" spread far and wide during 1950s as an easy and politically neutral greeting unlike the impractical to pronounce and politically loaded greeting "Čest práci!" (often shortened to simply "Čest" by communists themselves).
By 1960s the greeting "ahoj" was so common and widespread that it wasn't unique to any social group anymore. Poor/rich people, workers/intellectuals, young/old, men/women/kids, city/countryside people, everyone was accustomed to the greeting.
While the greeting "ahoj" is not exclusive to canoeing anymore, there are still some paddler etiquette rules alive and riders use a specific slang vocabulary. When canoeists or any other small river boat riders (kayak, raft, etc.) pass each other while riding, the only proper greeting is "ahoj".
Canoeing, kayaking or rafting through rivers is considered one of the Czech national sports. River weirs can get so crowded from spring to autumn that sometimes you have to wait in a boat "queue" before it is your turn to ride through.
