Parts of a PWC hull:

Sponsons: 

Q: What are sponsons?

A: Fins on the stern quarter of the PWC. 

Q: What do PWC sponsons do?

A: Improve handling on corners by digging into the water during a tighter turn. 

Strakes: 

Q: What are strakes? 

A: Ridges that run between the bow and stern of the PWC

Q: What do strakes do? 

A: Strakes create lift helping the PWC get up onto the plane. Once on the plane these strakes improve speed performance by reducing the wetted area on the hull (I.E. reducing water friction) and can improve directional stability.