There is no way around it - increased drag = increased effort.
Even if a weighted boat does not decelerate as quickly as when unweighted, it will take more effort to recelerate (new word!) back up to the same speed on the next stroke in the heavy one. Put another way, you will go faster in the lighter boat if you put in the same effort.
I imagine there are edge cases, like hurricane force headwinds impacting the higher hull more, submarining to go below the chop, etc but otherwise physics doesn’t give out freebies.
The short answer is no, the heavier boat will require more energy to maintain speed due to increased displacement and wetted surface. The long answer is it depends, because you are not a uniformly efficient propulsion source. For example, if you find it less personally fatiguing to take 1 very powerful stroke every 30 seconds versus 1 stroke half as powerful every 15 seconds, you may feel better with the heavier boat because of its superior glide. Usually, this kind of warped perception of effort will improve with training.
So monkeyhead, I think @pbailey makes a couple of key points.
F=ma
F(paddler) - F(drag) = ma
So assume one kayak of 200 pound total weight and one 300…and for a moment assume the drag forces are equal. And assume you put the same Force into each boat.
Then the math says the acceleration of the 300 pound boat is 2/3 that of the 200 pound boat for a given Force. But the deceleration between strokes is also only 2/3 of the lighter boat; it’s harder to accelerate but slows down less between strokes. So one key point is that the overall work is basically the same but the character of the work is different.
But the drag forces aren’t equal. Skin friction is based on wetted surface area. That gets worse and is a penalty in the heavier boat, no way around it. I believe that the main component of shape-induced drag is usually defined by a shape factor (Cd) times the frontal area (which gets worse with weight). So for the heavier boat to be more efficient overall, the boat’s shape in the water would have to improve enough to offset the penalties in skin friction and displaced water. So another key point is that this would be rare…an exception. I think the Blackhawk Ariel 15 foot solo canoe is one case where this mightbe true (it feels a lot better with a load). And I do believe I feel some benefit of more ideal trim in some solo canoes when a load is added but I have no idea if overall drag is less.
The heavier boat will also yaw less (track better) than the lighter boat so the losses due to yaw (over 10% in one reference I saw) will be less. Might be relevant in shorter boats with more rocker.
Overall, although most boats probably just feel “more burdened” with more weight I do think there are cases where it’s not so crazy to prefer more weight. In a canoe like a short 13-14 foot freestyle canoe the lack of glide can drive you nuts when cruising longer distances so to me a load smooth things out and helps quite a bit. I wonder if shorter kayaks or whitewater kayaks wouldn’t feel better to many paddlers with a little weight to help improve momentum/glide and reduce yaw between strokes. At the other end I’d wonder if some of the expedition kayaks meant to carry big loads don’t feel better to some folks with a load in them.
I wonder about ergonomic effects. It just seems like it’s not just about the boat but also how the boat/paddler work together.
My Current Designs Expedition was built to be really fast with a load. It will lose less speed loaded than most kayaks. It is still not more efficient with a load. Does it feel better loaded? Definitely even with just 20 pounds ballast / gear and my 240 lb. Glide further with the weight no.
In the automotive industry, they are continually looking at ways to reduce weight to make them more fuel efficient. I would argue that the same physic principals would apply to paddle craft.
