In my video the wind was about 12-15 knots (I thought it was less than 10 when I choose this kite size) and the boat speed was about 10 knots I think ( not sure I have little experience in boat speed estimation); there are some driving specificities like upwind turns that are more tricky than gibes (on a small boat, if you loose the dynamics, since there is a (impressive) risk to be pulled rearward by the kite, then hard to drive the boat and risk to damage the boat), but overall it is quite easy if you know how to drive a kite and a sail boat (the passenger had his first (memorable) trip on a boat on this video ...
It is quite open to the kite design choice, LEI or closed cell kite, everythink works (like on snowkiting) ; having to optimized it for a slow and heavy boat, I would agree with this :
tomtom wrote: ↑
Tue Mar 19, 2019 5:26 pm
Grunty kite is kite with profile optimized for low flying speed - so it has "grunt" even while flying slow. Typically this means deep heavy cambered profile.
Looping the kite can solve low boat speed - although only downwind.
... and indeed go for a grunty kite rather than high L/D ratio kite like race foilers, in order to get more “torque” as it has been explained, but also stability and relaunch; relaunch requires to have a good keel and put the boat perpendicular to wind (but certainly less sensitive for a >1 ton boat); maybe a nasa wing is however a bit exaggerated if you want to keep an acceptable wind rang and upwind angle (and not relaunchable);
For a little boat like 420 or the Lynx model on the video, the kite size should be approx the same as for kiteboarding; it can be even smaller (since you do not have the limitations of both waterstart and upwind planning), it works but just involve less boat speed; I tried with 15m and 12m foil kites and also 9m and 14m LEI (inflatable kites) ; so the bigger the best , but I would not go for a far larger kite than kiteboarding (depending on wind range off course) since the higher force may lead to accelerated wear if you use a serial model of kite;
I sometimes attach the kite to myself because a fixed point will give you almost no signs of over-power (and kite/line damage) . At least , when attached to you, you are ejected from the boat in a high gust, rather than damaging kite or boat ( better for a test but not in your application) ; but when you are in the suitable wind range, having a fixed point is faaaar more comfortable (and you can move more easily walk around the boat without changing the pull point) ; attachment point needs to be close to the keel to avoid impacts of kite directions and wind gusts on the boat directions; the lower it is , the less boat inclination you get , so I prefer a lower attachment point, for passenger comfrots and keel efficiency; be careful it should withstand all traction directions from horizontal to vertical, but also 360 degree angles ; overall you get a good stability of the boat, almost comparable to a standard sail;
Now, about automatic driving : having a full auto-pilot system seems tricky, but … I am quite sure (not tested however) that you can get a kind of auto-stable kite , in the altitude you want (so enabling the actual pulling of the boat), by taking advantage of the large width of your boat : indeed , by routing the rear lines through pulleys at portside and starboard extremities of the boat (i.e. left and right extremities, at keel level approx) and then after the pulley, connect them at the boat center to a kite bar or a trolley ; indeed, (during a travel perpendicular to the wind will be the most remarquable), when the kite starts to go down to the water, it will pull on the upper rear line of the kite which will force it to get back upward ( and reversally); you will even be able to set this neutral balance altitude point by just relocating the trolley closer to starboard or portside;
Be carefull, kite will be more tensioned than kitesurfing, so it may wear more rapidly ; you need strong lines, and strong kite.
A (old or recent , whatever) Peter Lynn arc model could be a good candidate , as it is solid , robust in time, and has an auto-zenith ability on front line that could ease the start of the kite in the middle of the water with less operators ( but not tested) ; and you can find very cheap ones for your first tests ( I think it is not worth spending the price of a Soul at the start …)
Hope this enlight a bit your research ...