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WhiteofHeart said..
I think you're still missing 1 critical point of longer harness lines and that is detaching the sail from the sailor in terms of balance and pressure on the foil. With short lines, your sail and you are quite solidly attached, if your sail gets yanked in a gust, you get yanked in a gust and the balance shifts completely. With longer lines the sail can get yanked, but your body can stay put. This is the main reason for me to ride longer lines on the freeride kit. This is regardless of whether or not you dedicate fully to the lines. With my freeride kit I often dodnt have my sail closed anyway, so no dedication really happening there.
If you do dedicate fully to the lines:
In light winds I ride shorter lines regardless of kit choice, as shorter lines are more efficient in terms of power delivery. Any bend at the hips (and/or knees) which is required for weighting longer lines reduces efficiency (and increases control).
Shorter lines (but arms fully extended) moves your shoulders/upper body further away from the sail and puts your body in a naturally rigid 7 position, increasing efficiency. Longer lines moves your shoulders/upper body closer to the sail, less rigid, but lowers your overall weight to increase leverage and thereby increases control.
I would never go as short to need a bend at the elbows, as a bend at the elbows would be indicative of a setup where you start getting worst of both worlds, as you reduce efficiency (distance between your shoulders and the sail), and reduce control (raised center of mass) at the same time.
The maximum length for me where I can extend my shoulders away from the rig maximally and still reach the boom is 28". Anything above 28" and I cannot reach the boom anymore with my shoulders pushed away from the rig (and would thus ride with a bend at the hips to be able to reach the boom). 28" is the optimal harness line length for my body / boom height for maximum efficiency. Anything below will decrease efficiency and control, everything above will decrease efficiency but increase control.
@sandman read this again. Lines which are shorter than optimal (/cause you to have to bend at the elbows) decrease both control and efficiency compared to lines which allow a perfect 7. Efficiency here means power in the rig. In lighter winds in my experience the problem is often not power in the foil, but power in the rig, and having it as far away from you as possible while still remaining rigid (7 stance) means maximum power in the rig as the sail has the most projected surface area, and the least rake backward (resulting in keeping spanwise airflow across the sail to a minimum, increasing power).
Add to that that for a lot of well tuned foil setups, the foil can be overpowering the downforce from the sail in light wind, extending the harness lines to "optimal" length increases mastfoot pressure given any fixed windspeed, allowing you to ride with equal (or more equal) weight across both legs in light winds instead of having to lean forward, increasing efficiency (and thus speed / glide) even more.
For me this "optimal" length is 28", which is about as long as my arm upto the palm of my hand (quite logical I think).
In practice I often run lines a little longer, not so I can sit lower, but so that I can extend the rig away from me further in gusty conditions and increase control. In 15-20 knots with a 5m I dont have to be efficient, but I like to keep in control if a sudden gust yanks my sail all over the place.
To explain why I'm taking the time to answer your question: To me it doesnt matter whether you or LeeD are going to do anything about your setup, want to, or even have to (e.g. you dont have to be 100% efficient all the time right?). I just want to have clear for other users / people who might find this thread in the future that there is an optimal harness line length (for maximum efficiency), and that while it is dependent on a lot of factors, an optimal length can 99% be found at 28" +/- 1".
If you hold your boom at shoulder width, can fully extend your arms and maintain a straight posture without bend at the hips you've found the correct length. If you have to bend at the hips you're "too long" for optimal efficiency, if you have to bend at the elbows you're "too long" for optimal efficiency. The harness line length for optimal control is a lot longer (I think for me around 34", beyond that I start losing control because I'm too low / far away etc.), between those two "optimal" lengths its a tradeoff between efficiency and control.
If you dont have to bend at the elbows / hips, maintain a straight 7 posture and end up with 23" lines either you're a kid or kid sized person, or there's a serious mismatch in your kit (way too large sail for the width probably).