My daughter has a perception pescador pro 12 and I have the OT sportsman 12 and I can say is I have to work hard just to try and keep up with her mine is 10lbs heavier than hers and I do weigh more than her. But I think the hule design makes it harder to paddle the OT to the pescador.Just saying my experience. I’d like to add we have two different paddles as well that can also be making a difference as mine is bending branches ace plus and she has a carlisle magic mystic. I think my paddle blades has to much flex therefore losing energy that I don’t feel when using her paddle.
Trade boats and paddles and see what happens.
Two paddlers in one boat is not twice the weight. You forgot to add the weight of the boat. More people in the same boat, assuming the boat is designed for it, is almost always faster. That is why C2 and K2 boats will almost always finish before C1 and K1 boats in races assuming equally talented paddlers and boats of roughly the same dimensions and weight.
Not true. Case in point, there were boats built in WW2 of concrete. It’s about displacement, not weight.
Breye, I had to eventually accept that my kids had gotten stronger than I am. That’s why I always put them in a heavier boat. Doesn’t work , but they had a good teacher 
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Actually quite true. If the boat is heavier than the water it can displace, it will sink. It has to do with the weight of the boat versus the weight of the water that can be displaced.
Boats are still built with such materials as steel and aluminum. Some engineering schools used to have concrete boat races, maybe they still do.
They did up to Covid. I haven’t checked since. One of the paddlers in our club with a racing background has worked with Michigan State’s team over the years. Lots of evaluations of the boats & projects on land but they do race them.
Up stream or down stream? Planing vs displacement hull design will make a bigger difference. Heading down river with a heavy loaded boat the current does more of the work.
This is a great question. Boats have something called a planning speed, that is the speed the boat has to be moving to give it a slight lift thus reducing the drag of the water. You see this in speed boats. Adding the weight of the gear increases the rate the boat creates more inertia to overcome before reaching the target speed. Once that speed it attained, I find it easier to maintain with the heavier boat. I also like paddling a boat loaded with my gear. It feels more stable. A boat loaded with camping gear also means I will not be making a return lap on the day’s journey.
I have not mentioned head winds, tail winds or waves on the side of the boat, each of which is also impacted by weight of the boat.
I’ll expand the discussion to ask, which will gain you more efficiency: An ounce off your paddle or a pound off your kayak?
Heavier boats are harder to get going, from a standing stop. In some cases the momentum of the weight can overpower the wetted surface and make for a higher top speed.
In most cases the wetted surface friction wins. When I was racing there was a woman paddler who paddled a Westside Wave Excel, just as I did. She was a slightly weaker paddler than I but women have a different way of paddling than men do. Men tend to try powering through everything, women tend to use their whole body.
She was faster than I was in that Wave boat, because she weighed forty some pounds less than I did, therefore her boat had a smaller wetted surface, so less friction.
20 pounds off my waist
Kayaks are not planing hulls with human power.
Heavier boats with equal power are not faster.
It takes more energy to move more weight.
Bouncy kayak, my boat has a lot of rocker, I have noticed it does have a max hull speed for what my weight and strength are. I added a garmin fitness watch last year to track my speed and heart rate and such. There is a speed that I can feel the kayak lift on my pull stroke than lower as I switch hands, not a lot but it does kind of bounce. If I try and move faster there is not much improvement in speed but my heart rate goes up a lot. I have called this ‘max hull speed’ which is just over 4 mph in my kayak. I have been doing some distance racing to keep the grey away is why I measured these things.
Is this the boat almost at planing speed and then Falling off. Or have I just caught up to the bow wave?
Planing is the mode of operation for a waterborne craft in which its weight is predominantly supported by hydrodynamic lift, rather than hydrostatic lift. Many forms of marine transport make use of planing, including fast ferries, racing boats, floatplanes, flying boats, seaplanes, and water skis. Wikipedia
Again human powered kayaks don’t any description of playing I have seen.
Your correct on the displacement hull. From doing the math max hull speed is over 6mph. My functional max speed is about 4.5mph.
So still not sure on the why I just know my heart rate goes through the ceiling if I exceed 4.5 in my boat which reduces the over all endurance over miles.
Just don’t do it. Or get a faster (longer narrower) boat.
Never heard of anyone saying my kayak is loaded with gear and it’s faster and easier to maintain forward motion.
A lot of talk about speed has crept into this thread. The original question did not question whether or not speed might be improved but rather the ability to maintain speed for a given amount of effort (i.e., because heavier objects have more momentum such that between strokes there would not be as much loss of speed as the boat pushes more water out of the way).