OK, what you have is a 1989 Hobie 18 World Championship boat. That was the last time base-model Hobie 18s were supplied by Hobie Cat to an event.
The hulls looked like this:
The hulls were gray. You can see how the hull stripe swooped down and under the hull, similar to the Boomer stripe. There's no stripe on the inside of the hull, so it probably stopped at the boat centerline. The forward end of the stripe terminated at the bow number. The standard "Hobie 18" identification sticker is above the swoop. Above that is the "Hobie Alter Signature Model" sticker.
The "Hobie Alter Signature Model" stickers first appeared on boats in the mid-80's. They were put on boats that had upgrades from the factory, like EPO rudders and Harken blocks. Otherwise, the boats are just the same as any other.
I'll see if I can find a close-up of "Hobie 18" and "Hobie Alter Signature Model" stickers.
What I originally thought you were asking about was the 1989 Hobie 16
Nationals in Chicago, IL. The same splash graphic used on those boats was used for the 1989 Hobie 18 Nationals in Erie, PA. That was the last time Hobie 18s were provided at an event - and they were Formula 18s, not base-model Hobie 18s. Competitors were not happy. Those hulls looked like this: