Seamen are very superstitious, to this day. (Actually, aren’t we all?)
This “Sunday sail, never fail” superstition arises from Christ’s resurrection on a Sunday. The worst day to go out sailing was believed to be Friday.
Even though there’s a hair-splitting theological debate on whether Christ was crucified on a Thursday or on a Friday, most sea-farers declined to debate it any further and decided to stick with the Friday choice.
The reason – I think – was that it gave them an extra free weekend on shore before embarking on a seven-day work week, for months and years on end.