Weight equalisation

If you want to make it more accurate by considering member deflections, teh system becomes much more complicated to calculate but fundamentally the overall system remains in static equilibrium.

Surely the forces are there but as the are perfectly balanced they create no movement, the tree roots are easily capable of balancing the mass of the 'sailor' so the force on them does not generate movement on the trunk. In a boat the force doing the 'pulling over is the power of the rig and the force doing the 'holding up' is the weight of the sailor, the analogy is not perfect as, because the boat can heel, they need to be in perfect balance. The position of the harness hook is still irrelevant though (excepting the physical effects on the crew Mozzy mentions)

Agreed... Enlighten us then?

changing the heights of the hook or termination on the mast obviously won't effect the moments. But it does change the forces which is of some importance to both the mast (and it's shape and structure) and the human body. 

Hook height... the further you place the hook up the body the more weight is on the feet. If you move the hook very low, you fall out backwards (or have to start tucking you feet under the gunwale). Generally I prefer a lower hook as it gives a bit more freedom to move the upper body around. 

If the hook height is very high it gets in the way, but also means more strain holding you bum up with the glutes. The same could be said for a low hook height and holding you shoulders up with your abbs (but you have shoulder straps and back support for that). 

Hook height on the mast is usually just set to the hounds as from a structural point of view its the best supported point of the mast and usually is still about full section before the mast tapers. So there is less you have to do to the mast to modify it to carry one or more sailors. 

What is also noticeable on the 800 with the equalisation it that as the racks go out the wires pull you inwards more. So you generally have more load on your feet. The negative is it's noticeably harder pointing your toes. But on the positive side when the boat comes on top you can have more heel before you start to swing away from the hull. 

Most 800 set their rigs up the same (or attempt to). Initially this makes a lots of sense as there isn't much variance in righting moment or all up weight so the theoretical fastest set up for all would be the same. But that lien of thinking doesn't account for how the varying body sizes load the rig and from which angle.  First of all the heavier sailors will put more compression in to the rig (duhh they're heavier) which means their windward shroud starts to flap around sooner. Lighter sailors will produce less compression, but also their wires pull more sideways. 

This creates a bit of a catch 22, where 800 sailors who are very light might be able to run less tension as they are unlikely to get the windward shroud flapping, and they will get little extra compression due to body weight on the wires which can leave the rig over straight and have them feeling over powered, despite the equalisation system giving them the same RM.  Whereas the bigger sailors might end up with flappy shrouds, which means they are getting more mast compression and more mast bend making their rig feel less powerful. Those problems are eventuated the further outside the weight range. The answer would be adjustable spreaders to get the correct mast curve with varying tension, but the spreaders are fixed. 

Interesting stuff, I think. But I don't want to derail the enthralling discussion about whether hook height changes the righting moment.