any motorized expedition revolves around fuel, all watercraft are on the low end of mpg, find enough fuel stops within range of each other and youre good to go
as for towing a second pwc, im pretty sure it wont plane out, you have to remember you'd be towing it from the lowest point of the tow pwc to the mid point of the towed pwc (front hull hook)
on top of that i doubt those anchor points could handle that much stress, now that im thinking about it
Right, so modifications needed. Some type of structural enhancement for the tow, I'm thinking a strap of steel running back along the length of the hull and fiberglassed in. The tow is clean slate, and the only reason to use PWC hull is that a lot of the work is done.
Adapting a version of ocean-going tug apparatus seems doable. Or outside marine applications, somewhere out there is a cable drum with a mainspring inside of it that can pay out meters of tow line and return it damped to a default position with no power input at all. There has to be a thousand ways to go at that.
Also out there are the equivalent of a PWC small block chevy and impeller pump and all that crap.
Nobody seems to be hypermiling a PWC either. Everyone here has nursed a hundred half-assed machines home on fumes. Fuel metering vs distance travelled is off-the-shelf at this point. I'd think that within a couple of days you could plot out some way to preserve fuel economy. And as far as pump and motor matching goes, what's been offered by Manufs. isn't necessarily the best combination.
The biggest thing I see though is that PWC are set up for transient performance and there seems to be a LOT of engineering room there to take all those pieces and make a fuel-efficient machine with existing crap. I don't see why Cruise Control should be out of the question, seems like a smartphone, aftermarket box, arduino, or raspberry solution. Or mechanical things.
I think the 'Engineering' way to go at it is a governor mindset. Find some RPM that the power combo works in and work to maximize that little slice. The problem seems easier than making a PWC that will satisfy consumers from scratch. Because PWC seek (and accomplish) to please All Men, there is a ton of room there to narrow it to what I want: Sit on it with my hands on the handlebars not operating the throttle for 8 hours a day at the same RPM, with a minimum of surging and pulling.
Barring all of that, putting some type of powerplant into a home-built hull that hydroplanes doesn't seem ridiculously hard.
But I think it would be fun to do it as stock as possible, as in just a few modifications on used stuff and go. The way a solidaxle Toyota pickup back around 2000 was easily modifiable in a minimalist sense to make it this weirdly OP thing. Black pipe sliders, welded diffs, bent brake-line brackets, long shocks, Chevy (better yet junkyard random) leafs, square-tube driveshaft.... You can do that with an angle grinder, propane torch, 110v welder, a drill, and handtools. There's got to be that for PWC.