Only accelerating relative to the land. The boat isn't in motion relative to the water, and so does no work, expends no energy, feels no accelerating force, and isn't subject to relativistic time dilation; likewise, analogously, galaxies.And yet a boat on a river that was increasing in speed, would still be accelerating, even if it was motionless in relation to the water itself.
The increasing dark energy doesn't violate conservation of energy because the expansion of spacetime has an energetically negative equivalent gravitational complement. At any stage in the expansion, the total 'positive' energy of matter, radiation, and dark energy is exactly balanced by the 'negative' energy of gravity (e.g. spacetime is warped by mass; that warping is gravity)....I see no reason to accept magical expanding nothing that would violate every known physical law including conservation of energy.
Also it's worth noting that, for the universe as a whole, energy conservation is not a requirement, as it isn't subject to the symmetry constraints of Noether's Theorem.
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