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Perceived instability after adding battery bank

Discussion in 'Technical Discussion' started by cgoodwin, Nov 26, 2014.

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  1. cgoodwin

    cgoodwin Member

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    Don't know what this turned into a fist fight last time, how about we suspend egos and try to just have a factual discussion...

    The vessel is a 1952 Feadship, 56' LOA, 13'2" Beam and a draft of 4'6". Steel hull, twin 671 detroits.

    I just finished installing 16 AGM batteries weighing 100lbs each. They were installed almost exactly in the center of the vessel lengthwise. They are just slightly to port of centerline and are about 20" below waterline.

    As soon as I installed the bank I noticed that the vessel has become "tippy", as I step onto the side deck from the dock she now noticeably rocks, which she had previously not done.

    I must say I'm a bit confused as I would think that adding 1600 lbs of weight below waterline would have made her more stable, not less.

    When I purchased the vessel she had 1200 lbs of batteries in nearly the same location although they were slightly starboard which served as starting and house bank, I now have 1600 slightly port, very slightly in that same location with an additional 200lbs of batteries outboard of each motor. Overall I have added an additional 800 lbs of batteries and that additional weight is distributed widely.


    In her original (from the factory) configuration she had batteries outboard of the motors, like now, and the battery bank was about 600 lbs and mounted starboard of center.


    This is a 64 year old vessel and has undergone many changes. Originally there was a genset on the centerline aft, at some time this was moved all the way forward and as far port as possible in the engine bay. A 50 gallon (500lb full) waste tank was also added forward and starboard. When I purchased the vessel the entire foredeck was rusted under the teak and the steel had expanded from 1/4" to nearly 3" of wet rust. I can not begin to calculate how much weight i removed by cutting this out and replacing it, but replacing the entire deck did raise the waterline about 2" on a 56' long 13' wide vessel weighing 28 tons...


    Looking at it mechanically, adding weight low would move the center gravity closer to the fulcrum point by lowering the center of gravity, this would explain why the action of weight added to the outside deck (end of the lever) would more easily tip the vessel. At some point in the history of the vessel this was obviously an issue as bilge keels were added.


    Attached is an image, top is the original config, middle in the config when I purchased and bottom is current. My question is if I can make the vessel more "Seakindly" by adding ballast in other areas?

    Attached Files:

  2. cgoodwin

    cgoodwin Member

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    Forgot to add the star banks to the final one...

    Attached Files:

  3. cgoodwin

    cgoodwin Member

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    Plan

    Attached Files:

  4. olderboater

    olderboater Senior Member

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    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.
  5. AMG

    AMG YF Moderator

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    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?
  6. cgoodwin

    cgoodwin Member

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  7. cgoodwin

    cgoodwin Member

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    All other loads are the same.
    All batteries are at the same level they were originally, I have not raised or lowered the floor of the engine room.
    Frankly the discussion turned into a pissing match and I stopped reading it as it seemed that those posting were more interested in insulting one another than discussing the subject.

    Purchased the boat and she was stable. Removed the deck and replaced, still stable. Removed all the batteries, still stable, added new batteries, seems "tippier".
  8. AMG

    AMG YF Moderator

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    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..?
  9. olderboater

    olderboater Senior Member

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

    cgoodwin Member

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    It is surprising that it reacts. She is only 13' wide so the "lever" acting on it is not great, in addition the gang way is only about 5' above the batteries which are just below water line, there is another 8" of space under them before the bottom of the boat. What surprises me is that I removed a great deal of weight from the boat replacing the rotted decks and all the old plumbing (mostly lead). Enough weight to expose an additional 4" of bottom paint at the bow (aft is just where it has always been). You would think that removing all that weight high above the center of gravity and buoyancy would have made more of a difference than 1600 lbs of batteries in the bilge.

    She has been in the water the whole time and I live aboard so while the changes may be slight, they are noticeable to me. I may just fill the midships fuel tank with 475 gallons of water now just to see what kind of difference that makes.
  11. jhall767

    jhall767 Senior Member

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    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.
  12. cgoodwin

    cgoodwin Member

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    Good thought, I actually have one in my iphone.
  13. Capt J

    Capt J Senior Member

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    Here are my thoughts and I am not a naval architect. If the waterline is the same at the stern but 4" high at the bow. I would move the entire bank and get the boat to sit at the same attitude that it did fore and aft. Having too little weight in the bow area might be making the boat too tippy. If the fuel tank you have fuel in is full and aft, why don't you transfer that foward to the midship tank (rather than filling a fuel tank with water) to see if moving weight foward and taking away from the aft will help.

    Quite honestly, I would email Feadship themselves with what you posted here and the information. They built the boat, have the naval architects on staff, and quite honestly would most likely be more than happy to be interested in helping you with one of their earlier builds.
  14. Bamboo

    Bamboo Senior Member

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    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?
  15. SeaEric

    SeaEric YF Historian

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    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.
  16. Kafue

    Kafue Senior Member

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    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.
  17. SFS

    SFS Senior Member

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    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.
  18. TeKeela

    TeKeela Member

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    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.
    Last edited: Nov 28, 2014
  19. cgoodwin

    cgoodwin Member

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    No Capt. Pedantic, but it is what I have in hand and since we are talking about a sense of "tippyness" one might assume that it could be useful to reflect noticeable changes while moving things around at the early stages of examining this issue. I am fairly sure that the electromagnetic bonds which hold electrons in orbit are not going to suddenly cease to function and all matter as we know it will not dissolve into the ether taking with it me, my passengers and the surrounding vessels simply because I checked the level app on my iphone. That said, I have read that early development of this app took place aboard the ill fated USS Eldridge...
  20. cgoodwin

    cgoodwin Member

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    Capt.J,
    Brigand was constructed by Witsen and Vis and is as far as I know the oldest Feadship still afloat, other than brochures almost nothing is known about her.