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I think rowing is actually officially a Winter sport Internationally, not 100%.
The earlier days, and perhaps still, the Girls Colleges used to use the Boys Colleges boats, so apart from just competing for time on the river for training, you can't just jump from one boat to another as there are all sorts of fine tuned settings for each size, style and strength of oarsman.
It would be a logistical nightmare having to change your rigging every day, there is enough angst from the Boys that the Girls even use them as historically they used to come back a bit worse for wear.