Jet propulsion watercraft

A ride plate assembly for a jet propulsion watercraft, the jet propulsion watercraft including a stern having a bottom surface and a water jet propeller, said ride plate assembly comprising:

• a ride plate, said ride plate for forming a lower part of said water jet propeller, said ride plate being removably mountable to the stern through a plurality of bolts extending through bolt holes formed in said ride plate, said ride plate being provided with a step portion and a higher level surface, said step portion extending in a width direction of the watercraft and including a lower level surface and a surface extending from said lower level surface to said higher level surface, said higher level surface being at a level higher than the bottom surface of the stern and said lower level surface by a predetermined dimension in a direction toward said watercraft when the ride plate is mounted to the stern, and said higher level surface and said lower level surface together form a bottom surface of said ride plate;
• and
• at least one vent hole, said at least one vent hole passing vertically through said higher level surface of said ride plate at a position thereof close to said step portion.