I was under the impression that 'toe the line' came from the British Parliament, where there are two lines drawn on the floor of the House of Commons main chamber, in front of each 'front bench' - the first row of seats where the Prime Minister, leader of the Opposition and deputies sit, opposing parties facing each other. The line is a few feet in front of each row of seats and the space between is just over a drawn swords' length on each side. Crossing the line was a distinct threat in the days when all men carried swords, daggers and multi-purpose knives, and to 'toe the line' was to go no further forward than your toes on the drawn line. It was supposed to reduce the possibility of blood shed and the Speaker could order anyone who overstepped the mark (there's another one) to back up and 'toe the line'. It means to stay in your place and abide by the rules and wasn't anything to do with nautical practices.

But I may be wrong.

LTS