A quick calculation, given the dimensions of the rollers and the density of oak (680Kg/M3), gives a weight of roughly 1/2 ton each. 15 rollers alone would weigh 7 1/2 tons.
Where would the flax for the sails have come from? Flax prefers a deep and loamy soil to grow well, which is in very short supply on Salisbury Plain.
Jim.