Perceived instability after adding battery bank

I don't know why you restarted this. Do you anticipate a naval architect showing up here and giving you the answer based on those drawings? You saw the discussions between some very knowledgeable people. And you know the answers indicate either way problems with what you did. One point missed while arguing having the batteries outside the engines vs. the vertical issue was that by putting them outside you are automatically raising them, so regardless of whose argument is right you meet both requirements.

Do not try to correct one mistake by adding ballast or trying other things that might complicate the issue more. Deal with one at a time and that means move the batteries you just installed. Might correctly placed ballast make it better? Sure, but it might worsen it. Determining would require some complex calculations. Personally I think adding ballast and lowering the boat more would be counterproductive. Don't fix one problem by adding another.

Also, find someone locally whose knowledge of these issues and stability you trust. Use them to help you decide the best place for the batteries.

Hi, when you say previously, is that before the deck was redone? Further, do you have about the same load in all tanks and compartments?

Yes, it will be "tippier" with more weight deep down, but the percentige to the displacement is so small that it is a little surprising that you react on it..?

Several of those things could have contributed and just the final move finally put it over the edge.

I suggest you get a digital level at your local hardware store. You don't need a big one just 12" long will do. You can get one that is accurate to less than 1 degree and has a zero reset function. Depending on your setup you might need an observer to read the numbers. Set it on a stable surface and set to 0. You can then move to one side (gunnel) and record the heel angle. Try the same with the other side. You could then fill that tank and repeat the process. If plausible you could also move the batteries and record the heel angles. This will give you a good idea of what is actually happening and how to position the weight to your liking.

Really? Your vessels stability and the safety of your passengers, yourself and others you meet on the water is going to be based on a iphone level app and you walking around + moving heavy items which you have decided to add to the vessel?

I have nothing to add to the stability discussion but I would like to remark that she is one handsome yacht. I'd love to see color photos.

Not being an engineer or architect, just an experienced boater, I have a Basic question:
Are you certain the adding of batteries is the cause?
Have you checked the bilges for water ingress?
Just because the issue seemed to coincide with the addition of new batteries does not rule out other causes, especially as the position of the new batteries has resulted in conflicting, expert opinions. It would not be the first time that a boat owner has chased the wrong goose!

Speaking from experience, just one example was when qualified mechanics who had recently rebuilt a gearbox on my boat and when it failed they assumed the work they had done was incorrect, removed the gearbox etc. End result was they had initially installed the incorrect oil filter ($50) plus had not taken the time to SIT BACK, re-consider causes and take an objective diagnosis, then act.

I have seen a similar issue on a recently restored boat. When it was relaunched the vessel heeled to one side. The cause was water leaking into a VOID in the hull (fibre glass) that had previously been sealed, however during the re-fit a new through hull fitting had been installed in the engine room, opening the void to a slow penetration of water. It took 24 hours for the void to fill and much longer to show itself to the owner.

I realise your boat is steel, yet there could well be a closed off sections not readily inspected that may have filled.

Have you installed any new through hull fittings?
Underwater lights?
Anodes?
New davit?
Transformer or similar electrical component that has a great deal of weight? How about the new inverter and associated gear?

When you removed all that moist, rusted steel, was it more to the port side or stbd?
Are you storing spare oil anywhere? I do because the engines are Detroits!

Just a thought.
As for the previous thread, hate to see a good brain and HUGE resource be lost over this argument.

As do I, and yet we all know that choices have consequences. What took me longer to learn in life is that the prices of various consequences can paid in many different currencies.

Are you boarding on the port side? And if so when you board to starboard it is not as "tippy", correct?

The drawings indicate you moved 600lbs of batteries that (assuming the boat was equally " tippy" port to starboard") were along the shaft line starboard balancing out a heavier port side. So taking out the 600lbs leaves a 600lb imbalance to port. Put those 600lbs back on the port side and you have made the port side not quite 1200lbs out of balance. So the port side is more "tippy" than it was before.

I'm sure someone here can make a calculation but since the 600lb shift is not equidistant from the centerline as it was before it does not make an equal weight transfer. Plus add say a 200lb person getting on board and your approx 1200lb imbalance is closer to 1400lbs.

But this is just a guess of course.