9ac is a Spoonerism which involves swapping the front of words around. Thus my dishwasher becomes my wish dasher, and every time I step into a lift that says “doors closing” I flip it to “claws dozing”.
In the case of 9ac, Spooner understands or is well versed in the part of a wave you might ride along on. If you then swap the fronts of those words you get a part of a ship, in this case pluralised. I always think of pirate ships having these.