SYDNEY (AFP)- Four Australians with almost no seafaring experience were jailed on Friday (Feb 22) for hatching a "foredoomed" plot to sail a boat to the southern Philippines and overthrow the local government.

The four men - and two other Australians who have yet to be sentenced - were arrested in 2016 by police after buying a seven-metre-long boat and moving it overland 2,840 kilometres from the southern city of Melbourne to the northeastern tip of Australia.

Despite having almost zero sailing experience, the "Tinnie Terrorists", as the Australian media have dubbed them, planned to reach the southern Philippines and join up with Muslim separatists.

"The whole venture was poorly planned and, I fear, foredoomed to failure," Justice Michael Croucher wrote in his judgement.

"Given the ill-suited vessel they had and their lack of serious boating experience, it is hard to imagine that they would have made it very far past the breakers off far north of Queensland."

Paul James Dacre, Antonino Granata and Kadir Kaya were sentenced to four years' imprisonment in the Supreme Court of Victoria, while Murat Kaya was sentenced to three years and eight months behind bars.

The two other men, Shayden Thorne and notorious Australian Islamic preacher Musa Cerantonio, have pleaded guilty to the charges, but have yet to be sentenced.

In handing down his sentence in Melbourne, Justice Michael Croucher said the four men would not have been involved in the plot if not for the "charismatic and persuasive Mr Cerantonio".

Canberra has been increasingly concerned by homegrown extremism and citizens fighting with Islamist organisations abroad such as Islamic State in Iraq and Syria (ISIS).

The country introduced sweeping counter-terrorism laws in 2014 that include blocking alleged extremists from going overseas.