In the comments section of last week's post Jay made an interesting point that I wanted to go into a little more detail on. Dad actually owns a tandem (or two-person) kayak. I've got a couple of pictures from our camping trip to Killarney in 2008.
That's a pretty good look at it on the beach, and here's one with Gray and Jay fishing from it:
As you can see from the photos you sit fairly close together, but the guy in the back still has enough room to stretch his legs out. Paddling one of these boats takes a bit of coordination since, as the picture above demonstrates, if the person in the front seat is paddling back at the same time and with the same hand as the person in the back paddles forward, you'll hit your paddles together. It just means that you have to let the person in the front set the pace and it becomes the responsibility of the person in the back to match their pace.
As with all kayaks there are a number of designs for the tandems. I've seen boats that were a bit longer than this and had a distinct cockpit for each paddler, with a small hatch in between the two. Ultimately though you're not going to find many that are too much longer than that boat, since it already has to be fairly large to accommodate two people.
They can be a lot of fun, and on that trip Gray and I found that Dad's tandem was a joy to paddle. On a camping trip it can also add a bit of security; if one person on the expedition becomes injured and can no longer paddle the boat can still be operated by one person, pulling the other camper to safety.
The issue that came up in the 2008 trip was the size of the boat... and not in the way that you're thinking. In fact, in a lot of ways the boat is too small. Have a closer look at the top picture. You'll notice that if you remove the cockpit the bow and stern of the boat are actually fairly small. At best they're the same size as a regular kayak, maybe even smaller. What ended up happening on our trip to David Lake was that despite having four paddlers the gear got divided up into thirds. Gray and I really weren't carrying any more gear than Dad and Jay, but they had to paddle their own individual kayaks that we're just as heavily laden as our one tandem. We were constantly pulling ahead of them on the long, straight sections of the lakes because we were essentially in a boat that weighed the same as the others, but had the benefit of two motors.
In a lot of ways I think the tandem would be a beautiful boat to take with us on that trip for the very reason Jay mentioned in his comment: one boat makes for an easier portage. It could end up being a hybrid of the benefits of both the canoe and the kayak. In the end though I just don't think it has the carrying capacity to haul all the gear that two people will need to camp, especially not in the fall where we'll need some slightly heavier equipment.
All of that said, if you're ever looking for a recreational boat and are looking to treat kayaking as a couple's activity the tandem can be a lot of fun. If you can get the coordination down. I take no responsibility for any marital conflict my suggestions may incite.
Have a great week everyone.