I have a problem with seagulls ****ting on my dock and boat. I see electronic bird repellers. Do they work. Something else better?

This, in relation to your screen name, is priceless.

Thanks. Brad.

Most of the restaurants put up poles and string nylon like between them and across, etc. etc. The lines make it so they can't fly so they stay away.

You might also try putting a couple of these up on poles on corners of the dock. I used them in my backyard to ward off birds of prey (protecting small dogs), and it cut down on snakes too even. Cheap to try.
https://a.co/d/bHuwIl8

I've seen people use a fake owl before

snakes really see that and are effraid?

They can’t fly, so they stay away.

Seriously, I might give it a try.

Two things:
Yes, some birds of prey eat snakes, so yes.
When it came to the yard, field mice stayed away. Fewer field mice = fewer snakes & fewer birds of prey