In a tandem canoe, I would first decide on the position of the front seat. This will be dictated by how much leg room is required or desired by the bow paddler and can be dependent on the hull design. Hulls with fuller ends may allow the front seat to be placed closer to the stem. Boats without flotation tanks (such as Royalex or three-layer poly hulls) may also allow the front seat to be placed closer to the stem. Since that boat is composite, hopefully it has some float tanks built in. If it does not, I would seriously think about adding some flotation in the form of short, inflatable tandem end bags or foam blocks, else the canoe could sink out of sight. If you need to add flotation to the ends, you need to take that into account when deciding on the position of the bow seat.
Once you determine the position of the front seat you need to consider where the center of gravity of the two paddlers will be relative to the seats, and how you want the boat trimmed. I prefer to have boats trimmed neutrally, but I have found that many tandem canoes come stock from the factory with the seats positioned in such a way that the boat is trimmed bow light. Most people will agree that bow light is better than bow heavy, and a little bow light will not hurt.
Seat placement can get tricky in a boat with a hull that has a distinctly asymmetrical water footprint, such as a swedeform or fishform hull. Your pictures suggest that your hull is pretty symmetrical so you should not have to deal with that issue.
The center of gravity relative to the seat will vary from paddler to paddler, depends on whether they are sitting or kneeling, and how they sit on the seat, or how much of their rear end they put on the seat when kneeling. Anatomical factors such as femur length also come into play. But I have found that a good general rule is to figure that the paddler's center of gravity will wind up approximately 1.5" in front of the front edge of the seats forward transverse seat frame.
Lets see how that compares to the formula given by gumpus in post #20. A seat postioned with the front gunwale hole for the front seat 31.5" forward of the longitudinal center will put the paddler's COG 1 1/2" plus half the width of the front seat frame (lets say 5/8") forward of that hole. So the bow paddler's COG winds up 32 1/8" forward of longitudinal center.
If the front hole for the rear seat is positioned 35 3/4" behind the hulls longitudinal center, the stern paddler's COG will wind up another 2 1/8" inches in front of that hole, or 33 5/8" behind longitudinal center. So considering paddler's of relatively equal weight and a hull that is symmetrical below the waterline (so that the longitudinal center of buoyancy and the longitudinal center of length are the same) that arrangement will result in a slightly bow light trim since the stern paddler's COG is 1 1/2" farther from the longitudinal center of buoyancy than that of the bow paddler.. That is exactly how I have seen most tandem hulls come stock from the factory.
