I will never agree with Bob (fusioneng) that the TI is not a true sailing boat.
I hope it is a sailing boat, because I'm never going to put an engine on it. Fusioneng has done some extremely interesting things to his tandem. It is what he loves to do, but, he has modified his to the point where most people would not recognize it as a Hobie Tandem Island. As I said recently, (joking, Bob, joking!) his tandem is really a powerboat with sails to minimize gas consumption--we all want to save on gas nowadays. Well, maybe I wasn't totally joking.
Contrary to what some have said here, I pedal hard through a tack. It depends upon the wind, but the harder you pedal, the faster you will make it across the wind. Some times the wind is so strong, even with pedaling, you can't make through the tack. At that point, you have to do some of the other strategies mentioned here. Generally, simply furling the sail to varying degrees will allow you to pedal through the tack. I hate to furl my sail, but, no question, furling your sail at times makes for better sailing.
Just got back from a great camping trip--where, in my 7th yr of Hobie AI for camping, I learned a lot.