: I've had experience of towing an unloaded and unpiloted open boat (15' canoe)
: from the back of a big dugout canoe with an outboard. This is much like
: towing a kayak with no (or a disabled) paddler in it - it tends to weave
: about horribly from side to side. This causes a lot of extra drag and makes
: the towing boat harder to control. In any waves, it would most likely
: capsize the boat (my experience was on a fairly flat river in Ecuador,
: with a towing speed of six or eight knots, I guess). As soon as a reasonably
: straight-tracking boat (like a kayak, not a dinghy) is aimed off to one
: side it keeps going until the towing angle is quite high, when it then
: starts to turn back into the wake of the towing boat, but obviously it then
: goes tearing off to the other side until the force pulling sideways on the
: bow is enough to turn it back again ...

As our kayaks are so close to being unstable anyway, any additional lateral force above the centre of bouyancy is just not going to help unless it is precisely and perfectly directly above the centre of bouyancy of with speed, the centry of dynamic lift. ; and grab loops flop from side to side - espec with a high bow.
As their are a few imperfections in this world, offcentre pulls happen and instability results . . .

If you can make a fixed (non slipping) bridle that goes under the kayak from one front deck fitting to it's mirror, with a fixed small loop dead centre at the keel(so the pull comes from the keel), and if the fittings are strong enough to take the force of the pull(a stronger alternate is to make a complete profile bridle behind those fittings but have clips that fix it from rotating), the kayak will normally track fine loaded or no. At speed this bridle will be out of the water anyway.

(this presupposes that the tow is fairly horizontal, if not, more care will have to be taken to deal with the off centre forces )