Kite Engine Wind Power Scaling Riddle 

Also similar to the Vespa Sail Rocket where the underwater foil was pulling -> down

Showing that would have been a good idea Christian. The balancing forces are between the keel and the kite, the tethers transmit force through tension, the sailboat balances forces between the sail and the keel; transmitting power through torque/lever arm

A beta tester may be using one for the TransPac race, stay tuned. I know I've got my fingers crossed.

Hey thanks for commenting. monohulls are self righting, but if you consider the center of mass, there is a torque force exerted through the hull, spanning from the bottom of the keel to the top of the mast, that is why boats heel when sailing crosswind. You are right, monohulls are self-righting, so in a storm they can recover from a capsize, but monohulls and multi hulls can always benefit from an additional sail, especially if it requires minimal deck space. I was thinking this setup would work nicely on a solar catamaran or maybe a sailboat without a mast

Yes, the video could have explained this better. This is especially true for multihulls, as there’s a direct line of tension between the keel and the kite, with no mast in between. This eliminates any fear of heeling or capsizing, as the power is transferred through the tension of the line. The line is intentionally designed to be the weakest point in the system. If it breaks, you simply reel in the kite, swap the spool, and relaunch-perhaps with a smaller kite.