84 E30ECRR prop question

[pwcopy]

Six years ago, I bought a 1984 24' pontoon boat with this engine on it. The prop was a dinky thing with blades that looked like they'd been worn half way down. It also had a cap that closed the end of the prop where the nut fit on the spindle. I bought a new prop after consulting with a shop about the right size for the boat and engine, and it was an open, through-prop exhaust type. The engine has run great, so I don't think I'm hurting it. But why was the old (original?) prop closed? Just curious. Thanks for yr help.

[boats.net]

84 engine should have thru-hub exhaust prop, don't know why it didn't have one on it.