When I went a few years ago I didn't buy on the boat, and I think I would have saved if I had. I also found it hard to get them from a machine, as where I went, you had to obtain an age verification token from staff, even though the cigs were from a machine - without the token, no cigs!. Get em on the boat - easier.
Why don't you check the price of cigs on the boat on the way out then compare the price in holland if there cheaper there buy them if not buy them on the boat on the way back.