A good tool to get them right off is WD-40. When you maintain your boat, you should always have a spray can nearby to spray them on so they don’t stick to the hull and become part of it forever. I await your invitation.
You won’t believe how well WD-40 works on rusted metal. True, you won’t get them back to their original glory days. But maybe you can use them a few more times before you throw them away. At least then you won’t have to go to the hardware store so often.