Why does a gennaker/kite lift the bow?

so in that figure, which doesn't show the crew's weight, the kite is just about the only thing preventing the boat from an immediate nosedive, as all of the other forces act to rotate the boat nose down

Lift is very dependant on the rig - clearly a kite-surfer gets lift. Decades ago my grandfather also proved he could get a boat to go upwind with an ordinary kite. Definitely lift there!

You sort of "hang" on the kite as the bow pitches down - that's for sure. You can see it especially in 12 videos.

Just a quick one, the kite will generate some lift due to the shape and where the centre of effort is. The lift is not that great but it is there. The hull shape and sea state aer also contributing factors.

In boats where the kite is say 20 sq.m. and above or smaller ones in bigger breeze, you will see the top guys have their mains nearly on centre going downwind and so reducing resistance to lift the bow. Ease the main and the main input changes and the bow drops, so acting as a trim tab. Work through the physics and you'll see how it works. A conventional kit, will also generate lift if deep broad reaching to running but here the main may change the dynamics here.

Bye for now

Originally posted by seamonkey    ... if with the kite up we have relatively reduced bow-down tendancy we have lift in the combined system as a results. THat is what people experience and that is what matters.   ....

well put, sir!
In an RS400, if you round the windward mark in moderate waves and pull the pole out, then dither getting the kite up, you will sometimes be sailing along with the bowsprit in the water.
Once the kit is set,   you speed up, the bow comes up and the world is a better, more stable place!