The attached image shows a fuse holder I replaced tonight, after it was discovered yesterday and taken offline. Both the fuse and holder are rated 30A. The fuse didn't blow. Where did the heat come from? I suspect the blades of the fuse didn't make full contact with the holder socket, and the connection heated up. Due to the melting it's difficult to determine why -- and I'm leaving it as-is in case the fuse-holder maker wants it for forensics. I have contacted their customer support.

I'm not saying at this point that it's a materials defect. It's possible the fuse wasn't fully inserted, in which case it might be "user error". Check to make sure YOUR fuses (and other connections throughout your boat) are all fully seated and making full contact. This could have turned out badly for me.