RR..is correct. Those wires are for bonding. You connect everything metal to a common bonding wire and then to a large bonding plate (zinc overboard)
Electrical bonding: Information from Answers.com
Many small boats are not bonded. If you have a lot of metal fittings esp if they are in salt water (inside the bilge and out) I would recommend bonding everything. If you trailer or have a dry bilge and fittings are dry inboard and don't have any 110 operating appliances plugged in, etc then you can get away without bonding.
It also is suppose to help for lighting strikes. Lots of people argue this but it is suppose to give the charge a place to go (ie the water) . The reality is while it might do this many boats hit hard by lighting loose some/all electronics bonded or not.
FYI...My boat is not fully bonded. If I was building a new boat I would bond everything and have a big heavy copper cable running from bow to stern in the bilge. I would also not wire everything like they did. But what is done is done and it works OK so the effort to fix it has a low priority at the moment on the mental to-do list.
BTW, nice paint job on the engine room. What paint did you use (epoxy, poly? one part or two) and talk me thu the prep process.