I was able to spend the afternoon alternating between my AI and my new Tandem. I weigh 190lbs, the winds were averaging about 10 knots with gusts from 15-18 knots. Wave heights were only 1 to 1 1/2 ft. My observations are only for the mentioned sea state.
In the AI, the tramps are in the way for paddling from shore. I have to reach backward behind the rear akas with the paddle to get any headway. On the Tandem, the rear seat is behind the rear akas and the tramps. Very easy to paddle out.
I previously had to put leashes on the AI aka braces to prevent possible loss of a brace in case of aka shear pin break...the TI has small coated wires connecting the brace to the akas.
I never did get the bungee cords to fit correctly on the AI Mirage pedals to hold the pedals in a good position...the TI Mirage pedals have small bungees to hold their positions.
On a beam reach, when a gust hit, the AI lee ama would consistently bury itself. On the TI, the lee ama was never completely underwater. I had to force the ama to submarine to see how the TI would handle it...the ama very quickly pulled itself back up...almost no torquing downwind.
Sailing fast into oncoming waves, the AI bow would almost always dig into the wave crests and water would flow into the cockpit. On the Tandem, the bow would jump (larger, farther forward amas?), the bow wave would move back about 3 feet, producing even less bow spray. Never got any water from the bow or sides into the forward (or stern) cockpit.
I am sure that with much larger waves, the TI would start to ship some water.
The AI amas are positioned much lower (less 'dihedral) and the windward ama repeatedly caught waves. The akas much more rigid and had little vertical movement. The Tandem akas and amas are positioned much higher but have much more play vertically (looked like a spring at times). The windward ama did not slam through a crest until I caused the hull to be overpowered.
The AI hull under all conditions acted as a 'displacement hull' pushing itself through the water especially crests. On the Tandem, the hull also acted as a displacement hull at low speeds. But in gusts, the bow climbed up, the bow wave shifted back beneath the hull, there was a noticeable sudden acceleration. It felt as if the hull was now on the wave crests and 'planing'! (I plan on having a friend video the Tandem and its attempt to plane). Moving fast (8+knots), the TI's 'triple rounded keel' with its large bottom area and 'flatness' felt as if
were skipping over the short-period waves. What a Rush!
I used a deck compass to try to check on how high the two kayaks could point. The AI was always 5 to 10 degrees lower in pointing than the TI. When tacking, the Tandem's greater momentum (and centerboard and rudder?) almost always carried me across irons without needing to pedal. About half the time I had to pedal to swing the AI.
Finally with the sails furled...I measured little if any difference in speed when pedaling at a
given rate. The AI seemed to slow down more when its smaller bow dug into oncoming
crests. The Tandem's longer length and weight seemed to carry it through a crest without
as much deceleration.
As mentioned I was not trying to do a scientific analysis of the differences...just my personal
observations and opinions. I am sure that having another person on the Tandem will change
its characteristics. But Hobie sure has a winner with the Tandem, especially for solo sailing!