So I bought a Hobie Eclipse Mirage...

[PonoBill]

Absolutely goofy fun. Great workout too. I'll keep you posted on the downwinding, I'm certainly going to try it.

[lanikaipaddler]

Hi PB - you ever get that Eclipse DW session in?  Very curious.

[PonoBill]

Yup, it was hard, but it was fun. I'd do it again. You can catch any bump with a mirage drive, even ones you missed. Just chase them down. It constantly wants to round up, but if you're quick on the rudder and bang the drive fins flat on the bottom of the board it controls somewhat OK.

[blackeye]

It's occurred to me that the mirage drive would make great propulsion for a R2AK vessel. If they could be mounted on the transom of a monohull, or somehow on a multihull, that would be awesome. If they could stay immersed. I have no idea regarding the relative efficiency merits of one human powered drive vs another, but on the R2AK it seems that paddle and oar driven craft are in it for the adventure, but the winners are sailboats with pedal-driven-propeller auxiliary power. Last year it was so light that the pedallers/paddlers/rowers had a say in the outcome. But the dual-pedal driven sailboat won.

But hey, Karl Kruger! Legend.

[PonoBill]

Just off the top of my head I'd think the Mirage drive would be ideal. With the pedals together the flippers are straight down and act as a fairly efficient centerboard. With the pedals away from each other the flippers are flat against the hull. And of course they can be pulled out easily and even replaced by either a plug or a better centerboard. The locking mechanism is stout. I don't know if Hobie would sell them individually, but they might get behind a serious effort. R2AK looks like a blast.

[Billekrub]

This afternoon I pedaled the Hobie to Wells Island and back. Anyone who is looking at the Mirage drive as a lower-effort water toy is going to be hugely disappointed. I basically drove a stair-stepper for four miles, and it felt like it.

I discovered something very strange. This thing is faster against a light current than with it. I was so certain I was just nuts that I did six loops, trying my hardest to hold the same cadence both ways. It's faster against the current. Not a tiny bit faster, about 12 percent faster in four tests fairly careful tests-- about 4.1 with the current for a steady, slow pace and 4.6 against the current  I don't know what the current speed is close to shore between the hook and the event center is right now. Probably one or two MPH.

I have a theory, see if this makes sense. The stair stepping isn't very much about pressing hard on the pedals--it's lifting your weight to the requisite height and straight-legging the pedal down. It's hard to feel any difference in resistance other than to say it feels like there's not enough resistance when I'm going with the current, and there might be a little more resistance going into the current.

With the current, the effective speed and related lift of water across the flipper foil is lower than against the current. The foil can generate more lift with that higher speed from the same cadence, but the higher lift means more drag.  Obviously the higher drag takes more energy, but it's hard to feel it because of the nature of the stair-stepper system. Just as obviously, at some higher current speed the greater efficiency is going to be overcome and the thing will go slower.

Anyway, that's my guess.

This suggests that the efficiency could be improved by at least 12 percent with a new design modification.  The long standup paddle is a terribly inefficient motor because the long arm reduces the force that a surfer can apply.  You need to build or adapt some better substitute prototypes to lead the way:  for surfing, for racing for exercise, for - - -.  Suddenly catching waves would be sooo easy even for non-surfers, AND one could increase stability with more board speed, not so much different than a windsurfer in light wind.

[Tom]

Maybe the reason its faster going into the current is the same principle as a sailboat being faster on a beam reach than on a down winder. The Mirage is powered by 'wings' that are flapped under water.  The pedaling  creates a difference of pressure on the wing which propels it by creating lift. With the current coming from behind, there would be less lift because there's less pressure difference on the wing.