All of your photos show a healthy blueish dust growing on the bronze or am I missing something?
1) The Gate valve had a sister, installed at the same time, which already failed.
2) Cheap plywood was used for some
of the backing plates, which is badly delaminated, moist, and literally falling apart
3) The head suction is most certainly not of marine grade components, and operates with difficulty.
4) The one glassed in pipe nipple has never given me any warm fuzzy feelings. Its sister has been replaced with a slightly better arrangement. Those two incidentally are the ones that appear in the best working condition.
5) I'm planning on taking the boat into COLD ICE FILLED WATER.. don't want to take ANY more chances than I have to! Anyone have experience with ice and SW suction? The only advise I have heard is don't stop.
The bonding you mention isn't advised as per whatever book I read last.. it changes. My understanding is by connecting them you create more potential for corrosion, since they are normally insulated by a fiberglass hull, and therefore have no potential to carry any stray current. However, the newer groco thruhulls come with a bonding screw now on the nut.. almost like they KNOW no one is using a flanged seacock anymore!
Working on the grid is always an interesting way to do bottom work, really makes you get organized and get the work done. I usually start work in the dingy before the tide is out all the way. One good thing, if you mess up you don't sink very far!
By the way some of those valves are quite possibly yellow brass such as that Red-White brand valve. I'd certainly switch those to bronze at the least.....
The "red-white" is actually coming from the holding tank and going to the deck pumpout.. so not a concern.
I wanted to get suggestions for sealant without leading the question, but from what I understand LifeCaulk will actually cure underwater, and if it gets 8 hours or so of airtime I think it might be just fine. I've used it on all my deck fittings with 100% success.. just not sure about thru-hulls.
Here is an example of a "good" day for an activity like this. I need at least 11 foot tide to get on the grid, so on this example I would float the boat on at 1am, get her positioned, start work on the hull (from dingy) at 5am, get her water tight by noon, can't float off until the 3am flood, so finish work between 1700-2000, float off at 3am. Sounds like a PITA but its not bad once you get the hang of it.. and save you a couple hundred in the bank.