Wiring Fail
This picture is an example of what can happen when someone who may be familiar with house wiring works on a boat.
In a house, the neutral and ground wires are connected together at the fuse box. But on a boat, this is a serious safety concern, and especially in freshwater, it's potentially lethal.
Tying the neutral to ground could allow 120 volts of deadly AC current into the boat's ground and bonding system.
If there's also a problem with the safety ground going ashore (not unheard of in marinas), all the underwater metals of the boat can be energized with 120V shore power. This can result in electricity in the water and, especially in freshwater, could injure or even kill nearby swimmers. Called electric shock drowning (ESD), the energized boat hardware creates a large electrified circle around the energized boat. When a person in the water enters that circle, he or she becomes paralyzed, loses the ability to tread water, and may drown.
The other clue that this installation was not done by a boat pro is that the wire is typical "Romex" solid-core type that's fine for a house, but because it's not made from stranded, flexible wire, can be subject to cracking from vibration and become a fire and shock hazard on a boat.