Blowing 30AMP fuses

Welcome to YF Kevin. The word "shoal" is confusing me, but do you have a meter on that line? If the 30amp breakers aren't tripping, you're drawing less than 30 amps. I'd have to assume that either the fuses are worn or there's a problem with the wires leading to them.

If your blowing fuses the load you have applied to the circuit is too much ( greater ) than the rating of the fuse.

Think I've got the picture. Guessing this is an older boat. Most of the 30 amp boats I run have a breaker inside the shore power inlet, and before the panel. It's a safety to keep a surge from making it to your panel. This is often prone to get spray and dampness. Put a meter on the pedestal to confirm you're only getting 30 amps, but I doubt that will be your problem as your main panel breakers handle the load. I think you may have a short or corrosion in the plug or that breaker box. Another problem could be with the fuses themselves. Electrical components aren't made as robust as they used to be. I'd be inclined to change that box out for a modern breaker.

Ralph, It might have escaped your attention, the main difference between a fuse and a circuit breaker is the breaker is re settable whereas the fuse is not without some remedial action in some and replacement in others.

As the OP mentioned he was blowing fuses and not circuit breakers I thought it prudent to continue to refer to the failing component using the same terminology.

Fuses are still widely used on brand new boats too.

It wasn't 30 or 50 amp ones I was referring to particularly but the actual apparatus.

Sometimes if the fuse holder has lost some of it's grip it will cause the ends of the fuse to overheat. I've had it happen on glass automotive type fuses where the ends got hot enough to melt the solder and the fuse element just came loose. It didn't blow, just lost contact inside the fuse.

I can only think of one word of advice and that is to get a qualified marine electrician. Blowing fuses. Fuse very hot. Fire. Loss of boat. Loss of life. Right now the fuse is protecting you. The problem may be very minor or more serious. However, the risk of not finding it or not properly fixing it is significant.