Alpha prop hub spacer

[Dnrbnsn2]

1990 Mariah 5.7 Alpha One. When I got my boat earlier this year it didn’t have the brass spacer for the prop. I got one and installed and it slowed the boat down at least 10mph, is this normal?

 

[Grub54891]

Pics with and without the spacer would help. Should not make a difference though.