What is "swingboats"

Usage examples of "swingboats".

And how, for heaven’s sake, did young men nowadays put their girls in an itching and asking when there were no swingboats to stand up in and bunch their muscles while they heaved on ropes like blue and scarlet catkins until the girls screamed for them to stop but not really wanting them to because it was so exciting to see Saint Laurence’s tower keep turning upside down and to know that the lads on the coconut shies were looking up their flying skirts?