I think you are right on point.
The PO kept those tanks filled with water all the time. They did not sail much.
I pumped out the water and filled with diesel. I also built a polishing system and I cleaned out the junk out of those tanks. They are full since and the diesel is cleaned regularly.
Your numbers might explain the tenderness I am experiencing. Even when I just walk around inside, the boat is slightly rolling for a while.
What I observed was, when the fresh water tank (274g) is filled, the tenderness is less. But only when it is completely filled. Once the water level goes down just 1/4 the boat is sensitive again. This water tank lays at the bottom, just above the bilge. The location is possibly the best for this weight, but not enough.
I bought 3 x 65 gallon water bladders and I used one of them in the forward cabin floor, filled with water. It did help I think, but not enough. So, I put the two other bladders onto the forward deck behind the anchor on each side and filled them with water. Unfortunately, they did not make any difference. That deck surface is way about the CG point, I suspect, so the extra weight is not helping, maybe even worsening the situation. These two water bladders pushed down the bow, so the regular 4-5 degree pitch is 2-3 degrees now.
I think the only feasible solution for improvement is extra weight at the very bottom of the keel, mounted on the I-beam. There is still a section, where extra metal bar could be mounted. I just don't know how much? The old survey I have shows 5000# ballast added somewhere below. Is it that extra metal bar on the I-beam? Is it the keel tanks? Is it the lead bricks in the bilge? It does not say. Maybe the combination of all these gives the 5000# ballast. So, it is very limited what more I can add below.
I thought about removing the lead bricks from the bilge area and using this lead to mold two heavy bars, which could be mounted on the I-beam. This would certainly move the weight to the lowest point, but I cannot tell, if this would make must difference?
Based on your calculations, removing the keel tanks does not make sense. As long they are full all the time, they add weight to the lower section.
The air tank at the stern has its own weight and practically it is at deck level, so it might not make much difference to have it, at all. It certainly does not help the sea handling of the boat, with following swells. Supposedly, it was added to help with ' squatting ' of the vessel. I think it helped with the squatting, but did not help with stability. By removing, it can improve sea handling, but I am not sure how would it effect buoyancy?
All these modifications were designed by a NA, after the boat was completed. The original hull plan was purchased from BR company, but BR was not involved in the process, at all. The hull was a motorsailer hull, 50-52' length and supposedly with much smaller upper structure and engine. Once they realized that it become top heavy, they hired a NA to design the modifications. The NA is not available anymore, so I cannot find any data on this story.
The boat is a wonderful live-aboard and an LRC capable vessel. Slow, but reliable CAT 3306, so it could sail far, as long the weather is not nasty. I am on the Columbia river now, so it is very comfortable to be here. We have some careless boaters generating wakes, but only during season. Sailing on the river is very nice, so I will just stay here. However, if the boat was more stabil, I would not mind to go out to the ocean sometimes and do some fishing. I still can, but it has to be when the weather is nice. Or, just buy the fish at the local store. Lol
I understand to get some reliable answers for possible solutions, I will need to find and work with a NA. If there is an affordable way to reduce the tenderness and make the boat more stabil, I will go for it in the near future. Nothing is urgent and it can take years, if needed. Secretly, I still hope that one day I will be able to go South and do some coastal cruising.
