When choosing harness lines:
Does not remember the shape therefore when adjusted from strong winds (short lines) to light winds (long lines) it will allow easy hooking in/out by creating a deep U-shape.
Because the tube is a soft one, it will swing during pumping. Therefore it will be a bit harder to hook in just after finishing pumping.
It does remember the shape, that means when you pump, it won’t swing at all making it easy to hook in and out while pumping.
Because the tube is so stiff, when the wind conditions change suddenly from strong breeze (using short lines) to light winds (using long lines) the tube holds the shape of a “pig’s tail”, not allowing the rope to hang low allowing for easy hook in and out.
Duolines have two points of support on the boom (see picture in the attachment). They are also the “forgiving ones”. That means if you set them a couple of centimetres away from the perfect spot on the boom but give a fist-width space between the two parts, it won’t cause problems – you will still feel the sail is in balance. It also allows you to adjust the lines for a bigger wind spread on the race without the need to move them on the boom during the race. You can always make duo lines into a “mono” by putting both parts next to each other on the boom. The disadvantage is they are much harder to move on the boom compared to Monolines.
Monolines have only one point of support on the boom. They are the “less forgiving” lines. Once you set them in a certain place on the boom, make sure it is the right one, otherwise the sail will not feel balanced. They are much easier to move along the boom compared to Duo lines.
Having monolines may mean you would need to move them during the race when the wind strength changes significantly (for strong winds move them back towards the clew, for light winds move them towards the mast). Duolines allow you to set them for a broader wind range.