1885 was a turning point

After 1885, there really was a great techological advance that continued to the end of the Century. In 1885, the British navy looked on the 17-knot Scout and her sisters as "ocean-going torpedo boats". They were already too slow for that role. Not very much earlier, 17 knots seemed fast. Soon, quite large ships would be able to exceed 20 knots. The French were leaders in building fast torpedo boats, which tended to lead the way and to drive the British to do better. The Scout was designed by Nathanial Barnaby as a "torpedo cruiser", a type intended to accompany the fleet and deliver torpedo attacks. You might think of them in the defensive role, as well, although they seem to have had 5in BLR guns, not QF.