I haven't paddled an ICF-C2, but I have paddled next to them quite a bit, and they are been paddled 100% in sync on opposite sides. I mean they look like a butterfly effect if you know what I mean (take a look a some videos).
I haven't tried it, but it should not matter. However, in a k2/k4, the leading paddler (paddler seated in the first seat) tends to be the one setting stroke rate and form -the paddler seating behind (motor house in a k2) tends to follow the first seat.
It is amusing to see how elite paddlers seating in the second seat tends to adapt not only their stroke rate but also their form to mimic the first seat.
Therefore, I think it is much easier to paddle a k2 on the same side than on opposite sides even if mathematically speaking is the same.
I get it in order for both paddlers to operate in synch well it’s easier to copy/follow/mirror the timeing of the paddler in front instead of opposite sides.
… I’m in the “who cares what the math is just go with what works camp” but I can see how for some this would be a fun problem to solve on paper.
But for the rest of us it doesn’t really matter. I like to paddle for fitness and race and believe that if it was faster to paddle out of sync at race speed then it would have been figured out a long time ago.
As for speeds slower than race pace, who cares. 4mph is so easy it’s boring in most boats and anything under that can be done in your sleep. Other than for the fun of the math I don’t see the benefit of finding out what’s more efficient at that pace. Problem solving can be fun though.
Understading leads to better technique Accurate understanding of how and why something works or does not work allows for the ability to optimize those techniques. The creation of an accurate model for why techniques work requires a very in depth study of how they work. With this in depth knowledge it is possible to make them work even better.
If all you know is “The fast guys do it that way” can lead to silly creations like the “Cargo Culture” where primitive people make things that look like airplanes because they think if they perform “ceremonies” like the modern cultures do, they will get the same results.
Where if you learn how airplanes work you can make your own, better airplane. Paddling in sync is not the only reason winners win, an accurate understanding of the physics of paddling will allow smart paddlers to paddle faster and more efficiently, and for those who care: win more races.
A formula and a comment about 6 posts down in the discussion might be particularly useful. The comment reads:
"To achieve a certain thrust you can either choose a little fast prop or large slow prop.
You get the same thrust as long as the product of m and V is the same.
But the power needed to drive the system is not independent of the two measures:
If you choose a little propeller the mass flow reduces and the velocity must increase likewise.
This means that if the mass flow is reduced by a factor of two - the V^2 terms is quadrupled.
This means that the power needed from the motor and battery is doubled!"
Anyone doing the math, be careful that to acknowledge in your formula that 2 out-of-synch paddlers each at (for example) 60 strokes per minute is not the same as one paddler paddling at 120 strokes per minute. The blade movement of the 120 stroke per minute paddler would necessarily be much faster -- even though the total strokes per minute in the two examples is the same.
The out-of-synch paddlers are producing 120 strokes per minute but each of their paddles is cycling at only 60 strokes per minute.
... methods that work well at one speed usually don't work well at another. Propeller designers have known "almost forever" that propeller size and pitch must be matched to both operating speed and load, in spite of the fact that using only the most BASIC of thrust theory would suggests it doesn't matter. In fact, not that many years ago, before boaters had such specialized equipment, it was common for a motorboater to have two props for the same motor; one for tearing around in the boat, and the other for pulling a water skier (and each prop was faster that then other when used for ITS job).
Misunderstanding of what's important and blindly believing that what's good for one form of extreme performance must be good for all sorts of other things leads to all sorts of incredibly stupid practices, like putting low-profile tires on 4x4 pickup trucks because what's provides good handling for sports cars (never mind that the footprint of the tire won't conform to rough terrain), or that craze in the 70s for hikers and backpackers to wear the biggest, heaviest, stiffest boots available because that's what the serious mountain climbers were using. Backpackers EVENTUALLY figured out that they were wearing very nearly the worst possible style of boots for the job, and if we are lucky, people might eventually figure out that putting low-profile tires on trucks that occasionally operate off-pavement is ridicuous too. By the same token, not everything that's good for keeping a boat going faster than hull speed is good for anything else at all. Some aspects might be, but it makes no sense to assume "all".
racing or not doesn’t really matter It doesn’t matter if you never get to hull speed.
If you are asking what is the most efficient means of propulsion then you look at the winning racer. Racers use the most efficient possible technique. Wasted effort = a lost race. You may prefer another method of paddling for reasons other than efficiency (like I’ll J a canoe just for the purpose of keeping it dry inside) but the race techniques are the most efficient for any reasonable cruising speed.
I can tell you from experience that it takes less effort to paddle a c2 at 5mph switching than it does to stay on one side with the stern man J-stroking. Typically when I’m touring in a canoe though I will J because it makes for a drier ride and the difference in effort at lower speeds isn’t enough to be a bother. Still, even when J’ing I’ll paddle in sync with the bow because it takes less effort to go whatever speed as long as we are maintaining a reasonable cadence and not totally lilly dipping.
For me the only difference between racing technique and touring is that I’ll shorten my stroke a bit when paddling slowly so that the cadence doesn’t become unfortably low. I might lower my top hand a bit as well since the higher angle can fatique the deltoids at slower rates when the recovery time is longer. The basic mechanics don’t change a bit. The same principles are efficient for paddling at 16-17kph over 1000m, 14.5-15kph over 5000m, or 12-13kph over 50,000m.