Sÿver?

In some old records I notice Syver is spelled with "ÿ"--two little dots over the y--looks like a delightfully happy little y. In handwriting it looks just like ij. I know there are variations of the name Syver like Sjugurd, Sjurd, and similar. I know there is a letter called the Dutch Y that is ÿ. I'm interested in finding out why Syver was spelled Sÿver. I assume it had something to do with pronounciation. By any chance does anybody know anything about this? Thanks, Ray