The Canadian tax system as regards to seafarers is quite simple Pete, if you earn money anywhere in the world and you are a resident of Canada, you pay Canadian tax at the full rate. When I worked for Maersk through a Canadian agency in St Johns, there was a "tax reduction" for work in the oil exploration and exploitation field when working outside of Canada for an approved Canadian company. You had to be out of the country for 6 months of the tax year, 1st January to 31 December, in order to be eligible for it. The seafarer, however, never saw that allowance.
Lets keep things simple. The tax payable while overseas was reduced to 20% of taxes payable if you were working in Canada. In other words, if you were employed on a Canadian ship in normal trading and paid $100 in taxes, the amount owing while working for an approved Canadian company in the approved fields (oil exploration, etc) would be $20.
So lets say your salary was $100,000 and your tax payable normally 25% or so of that, or $25000. The "tax break" would drop payable taxes for eligible seafarers to 20% of this, ie, $5000. The Maersk bunch thought this was a great idea and waved the "tax break" in front of seafarers to lure them to "big, taxfree paycheques". Just one problem, THEY took the tax break and paid you the lower salary, in this case $80,000. If you did not complete 6 months of the tax year (Jan 1 to Dec 31 in Canada) out of the country, you were not eligible for any "tax break" and you paid full tax on every penny earned. For $40,000 paid for the 3 trips out of Canada in the 6 months between July and December, you still paid the full rate, ie 10,000, so the take-home was 30,000. This bound you to Maersk just as sure as if they had bought and paid for you. The taxman's whip was waved often. Remember, it's 6 months out of the country, with an approved company on an approved operation, between 1 Jan and 31 Dec. 6 months between 1 July and 30 May is just 3 months out of the country in either tax year, when one works day-for-day. (1 July to 31 December, and 1 January to 30 June) We were not, of course, paid for time off the ship, strictly flat rate for days on board. It meant, of course, that the Maersk agency were, in effect, paying lower wages than anyone else, and making profits by exploiting seafarers. Maybe it's not illegal, but it sure as hell is unethical and immoral.
Perhaps things have changed, but I don't believe the bandits, con artists, wide boys, spivs and exploiters of the shipping world have gone very far into the shadows.
Discourage incest, ban country "music".