We use qtVlm to compare the distance saving with a great circle route over a rhumb line route as a function of latitude and distance. As a guideline the saving is only significant when both departure and destination are at higher latitudes and the total distance between points is more than 2,000 nmi or so. Not to mention that a sailing route is usually determined by the wind pattern more so than the geometry, and the fact that a great circle route at higher latitudes often reaches up into the ice… at least for as long as there is any ice left!