We just bought a tandem kayak, we took it to the water and we can’t make it go straight.
My husband is bigger than me so he sits on the back. We rented kayaks before, so we are wondering if it could be the kayak or our lack of experience.
The outcome of all this is circles to the left. Then overcompensation and swinging to the right.
Tandem kayaks are less sensitive to all this, but it'll still work out the same, just more slowly.
This is fundamental to paddling in a straight line.
You'll have to regularly check your paddles to ensure that you're holding equidistant from the blades.
Ensure that you're rotating the paddle correctly and that it's going in nice and flat both sides, leaving it slightly angled on the weak side is very common.
Ensure that the paddle is going in the same distance from the boat on both sides. Closer to the boat will drive you straighter, further from the boat has more of a turning effect.
Going in circles while in a paddled craft such as a kayak/canoe/raft means that there is more force being applied on one side than the other (this is also how you turn the craft).
If you notice that you are going to one side, paddle more on that side and less on the other until the craft straightens out. All of this just takes practice and it gets easier with time.
The other option to look into would be getting a rudder for the kayak, as that will help but whether it would be possible depends on your exact model of kayak.
It might seem obvious to more experienced paddlers here, but it drove my wife and myself crazy while trying to paddle on a 3-seater kayak. We were sitting on the two front seats, without noticing the rear paddler should sit on the rear seat.
The kayak would turn around every 10 seconds. Could that be your problem?
Briefly: make sure the boat sits as flat and level in the water as possible. As others have indicated in their answers above, it’s not good if there is too much weight in the front (which can happen even if you are very light if the seat is very far forward—-think of a small kid at the very end of a see-saw balancing their parent close to the middle). But it’s also bad if too much weight is in the rear and not enough in the front. Because you say your husband is heavier, it’s possible you don’t have enough weight forward. A boat that is not flat is very sensitive to wind and paddle strokes. If you can, move your or your husband’s seats until the boat is as level as you can make it. Ideally, have someone look at the boat with you both in it, it should lie flat on the water—adjust the seats until it does. Definitely also practice the good paddling techniques mentioned in the other answers. Also, many tandem kayakers appreciate the convenience and control of a rudder.
General notes on making a kayak easier or harder to turn:
Going straight in a kayak is a competition between the forces acting to turn the kayak and the kayak’s “tracking”, or resistance to turning, from the shape that is under the water.
The main forces acting to turn the kayak are what you do with the paddles, the rudder if any, and the wind. In addition there may be a contribution from waves or currents, and any assymetry of the part of the hull which is under water, which may happen if the kayak is leaning to one side of the other (from putting much more of the heavy cargo on one side, or if you are leaning or sitting slightly closer to one side than the other).
The shape under the water that resists turning and promotes straight tracking is the combination of the shape of the submerged part of the hull, plus the rudder or the skeg if there is one (a skeg is basically a small rudder which always points straight and which can be raised or lowered a variable amount). The paddle can also be used to help the kayak track straight when it’s not busy paddling or steering (for example when on the face of a wave).
The important thing to understand is that all of these factors add up to influence how the boat behaves. Some of these tracking factors are inherent to the boat, and some may be changed. Specifically, how a boat is “trimmed” (where weight is placed) may strongly affect how strongly the kayak turns toward the wind, or how easily it turns in response to uneven paddling. Adjusting seat position (slightly because people are heavy) or cargo storage (needs to be significant) may very noticeably change this tracking performance.
Note that a steerable rudder is a very easy way to make a boat go straight and is a very welcome feature especially for new paddlers or paddlers in double kayaks. However, relying on the rudder to counteract asymmetrical paddling will cause excess drag and slow forward progress. For ease of travel it is preferable to learn to trim your boat flat and paddle symmetrically.
As a related side note: a typical sea kayak has a very different submerged shape depending if it is upright or leaned on its side aka “edged”. When upright, more of the kayak’s bow and stern, and the full length of its keel, are in the water, which promotes staight tracking. When edged, more of the kayaks wide hips are submerged, the bow and stern are lifted slightly, and the resulting shape is significantly less resistant to turning. As a result most sea kayaks can be turned more quickly when edged which is important for fast maneuvering. Additionally some kayaks are shaped such that they naturally turn in a particular direction when edged and can be actively steered by edging.
The tandems I have seen have rudders, not skegs, because people find them hard to turn without one. Depending on the type of rudder, it can be easy to set it so it is turned when your feet are in normal position. That will lead to the boat turning as you report. Make sure the rudder is centered when you are not trying to steer with it.
Your explanations could be correct. But from having paddled a flat bottom inflatable kayak I noticed that the "swirl" from the paddle would go under the hull and cause a turn. The solution is opposite that of a canoe. The person in front steers and the person in the back paddles. Thus the swirl goes away from the kayak and not under. Make sense?
The stronger person (if there is one) should sit in the rear. The rear paddler is also responsible for steering, even backpaddling for tighter turns. Bigger person, bigger blade, smaller person, smaller blade.
The person up front should simply paddle, and set the pace, but not too quickly (or strongly) for the rear paddler. When both paddle on the same side the person in back should dip just before the lead to prevent strikes.
Switch sides every few strokes. Sometimes there are rocks and you'll have to stick on one side or the other; otherwise it's better to be on alternate sides to loosen the timing requirements. To switch with a double ended paddle the lead simply pauses for a moment and then switches with the rear following (catching up on the next stroke).
This balances your efforts and distributes your exertion.
That should result in an almost perfectly straight course, unless you are deliberately turning. Try practicing paddling from buoy to buoy, figure-8 will provide slightly better tight turning practice.
Like anything with two people it takes practice and cooperation.