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  1. #1
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    Default AGM batteries pulling double duty as ballast

    I am looking at designs that have a fair amount of internal ballast and am thinking about using AGM batteries for that purpose and to power an electric drive, is there any reason this is not feasible and if not what might I be missing/overlooking about doing this?
    I know this is a pretty open ended question but I'm sure there is more to the placement of ballast than just weight and location, but in the size package I'm looking at space will be at a premium so IF this would be feasible it would be worth doing and taking this into consideration from the very beginning will make a better end product.

  2. #2
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    Default Re: AGM batteries pulling double duty as ballast

    You are on the right track. You need to make sure that the batteries will not get wet, will be securely fastened in place, and are vented properly. And, of course, know what you are doing when it comes time to wire them, or it could get pretty exciting in the ol' boatshop...
    Hope for the best, but plan for the worst.

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    Default Re: AGM batteries pulling double duty as ballast

    I wonder how many hours a powerwall would supply?

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    Default Re: AGM batteries pulling double duty as ballast

    Lots of people have used batteries for ballast, including myself. My opinion is there are the obvious considerations of what happens when you put all the ballast in a small area in the middle of the boat rather than more spread out as is typically called for with internal ballast, but whether these theoretical differences are going to make much practical difference is questionable, so you're probably not overlooking much, depending on the design of course. And as stated by mmd, there's always the chemical/electrical issues to be dealt with but that's all fairly obvious, too. Got a boat in mind?
    There is no rational, logical, or physical description of how free will could exist. It therefore makes no sense to praise or condemn anyone on the grounds they are a free willed self that made one choice but could have chosen something else. There is no evidence that such a situation is possible in our Universe. Demonstrate otherwise and I will be thrilled.

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    Default Re: AGM batteries pulling double duty as ballast

    Welcome to the forum! Absolutely feasible. Weight is weight. Remember, big wires; small fuses. And plan out what happens if you turn over.

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    Default Re: AGM batteries pulling double duty as ballast

    I'd suggest having a sump cavity of some kind that is lower than the batteries and serviced by a dedicated bilge pump, but I love the idea of low, center mounted mass.

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    Default Re: AGM batteries pulling double duty as ballast

    Yep, in principal. If the original design calls for lead in the keel, the battery weight won't be low enough. But if the original design calls for water ballast, you shouldn't have any problem replacing the ballast tank area with batteries -- you may even gain some stability.
    -Dave

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    Default Re: AGM batteries pulling double duty as ballast

    Quote Originally Posted by Woxbox View Post
    Yep, in principal. If the original design calls for lead in the keel, the battery weight won't be low enough. But if the original design calls for water ballast, you shouldn't have any problem replacing the ballast tank area with batteries -- you may even gain some stability.
    That makes sense and I have yet to settle on a design, I want something along the lines and construction of the working craft form the late 1800's to early 1900's I'm leaning towards heavy/robust as it will be used for trips of 3-4 days with my grand kids and I to fish/troll under sail and fish the coves with the electric motor on Lakes Mead,Powell and Havasau here in the Southwest US.

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    Default Re: AGM batteries pulling double duty as ballast

    Eggman918- Welcome!

    Your proposal is exactly my plan for my 18' TomCat. Before beginning construction, I consulted with designer Wm Garden (unfortunately, now deceased). As a result of increasing the length to 18', he specified that it would need "500 pounds of internal ballast" to quote him. Although I haven't yet reached the point of installing the electric drive system, the batteries will make up most of the required 500 lbs. For the rest, I plan to cast some blocks of concrete. Both the blocks and batteries will mounted along either side of the centerboard case between the floors, and further aft as needed. The blocks' final locations will be used to establish proper fore/aft trim.

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    Default Re: AGM batteries pulling double duty as ballast

    In my boating experience over the last few decades I have seen numerous minor flooding into boats. Sometimes it might be seawater, more often a tankage issue. Most of the time it's a non issue , gets corrected and the boat pumped out . 100 or 500 litres gone. We had a bladder type fresh water tank rupture last year ourselves.
    But those boats all have their batteries placed according to normal and accepted maritime practise. Which is somewhere they can't get fried by a little bit of stray water.
    $^&/ happens.
    Last edited by John B; 03-12-2018 at 10:03 PM.

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    Default Re: AGM batteries pulling double duty as ballast

    Sealed AGM's would be my choice, Lifeline etc can be mounted in any orientation too. Though it might be worth checking which type are the most dense.

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    Default Re: AGM batteries pulling double duty as ballast

    FWIW, my 19' Ralph Stanley sloop displaces 3000#, of which 1200# is lead ballast. Originally this was all inside, in 12# pigs, and was crammed below the floorboards. She was hull #1 of three boats built to the same design --sorta.

    Hull #3 was a bit different: she was built with an internal electric motor and much of her ballast was in her batteries. However, batteries are not as dense as lead, so not only did her cabin sole need to be raised several inches to accomodate the greater volume of her ballast, but her keel was notched and ~400# of lead was cast into an external ballast keel.

    After all that, however, having that big slug of lead down low contributed to her being the fastest of the three sisters, since she didn't heel as much, ergo she didn't suffer from the same degree of weather helm as afflicted hull #1 (my boat) and hull #2 (identical hull form and ballasting to my boat). So shifting that lead outside to accomodate the batteries turned out to be an advantage --as it might be for your boat.

    (Three years ago I modified my boat by melting down 450# of her internal lead and casting it into an external ballast keel, approximately duplicating the arrangement of hull #3. I made other hull modifications at the same time, but I believe the shift in the ballast contributed significantly to a dramatic increase in my boat's performance.)

    Alex

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    Default Re: AGM batteries pulling double duty as ballast

    The heaviest batteries are probably forklift batteries. They have thicker plates and very long life. For a forklift, the long life and higher weight are both advantageous. Having told you just about everything I know about forklift batteries, you will have to do some research to know if thid is indeed a good idea. My limited 5 minutes of google research indicates that They are not AGM batteries.
    Size capacity and weight example.
    https://www.warehouseiq.com/types-forklift-batteries/
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    Default Re: AGM batteries pulling double duty as ballast

    I'm pretty sure that Antonio Dias (website here: https://antoniodiasdesign.wordpress....01/18/welcome/) designed a sailing boat with a small cabin that had batteries as ballast and an integral electric motor. the 23 foot auxilliary here:

    https://antoniodiasdesign.wordpress....5/meet-buster/

    is the one I think ...

    It might be worthwhile contacting him.

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    Default Re: AGM batteries pulling double duty as ballast

    Hi,

    It looks like most larger banks are moving to lithium iron phosphate (LiFePO4) batteries, you might want to check them out before deciding to go with lead/acid based ones.

    Cheers,
    Mark

    https://en.wikipedia.org/wiki/Lithiu...sphate_battery

  16. #16
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    Default Re: AGM batteries pulling double duty as ballast

    Quote Originally Posted by Mark0 View Post
    Hi,

    It looks like most larger banks are moving to lithium iron phosphate (LiFePO4) batteries, you might want to check them out before deciding to go with lead/acid based ones.

    Cheers,
    Mark

    https://en.wikipedia.org/wiki/Lithiu...sphate_battery
    The advantage to lithium-ion batteries is that they are light. That's not an advantage for ballast.

  17. #17
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    Default Re: AGM batteries pulling double duty as ballast

    Quote Originally Posted by Dan McCosh View Post
    The advantage to lithium-ion batteries is that they are light. That's not an advantage for ballast.
    Hi Dan,
    I would said the advantage of them is the cycles / charge profile. Lead acid batteries aren't all that "dense" (~150 lbs/ft^3), so I would think you are better off with traditional lead ballast (~710 lbs/ft^3) and keep a separate battery bank.
    Cheers,
    Mark

  18. #18
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    Default Re: AGM batteries pulling double duty as ballast

    How does one figure out if the weight of the batteries will be sufficient to replace say the weight of water tanks? Given frame spacing and the fact that batteries might not fill the entire space will the density of weight be sufficient to replace the water and how does one figure that out? Maybe it's irrelevant if the water (or fuel as the case may be) would not weigh anything when the tanks were nearly empty so the batteries will certainly weigh more but at the beginning of a passage, when fuel and water are full, would batteries be the same weight? Lots of variables and it would be pretty boat specific I suppose but maybe Michael could lead us toward how we go about figuring it out?
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    Default Re: AGM batteries pulling double duty as ballast

    Quote Originally Posted by Sailor View Post
    How does one figure out if the weight of the batteries will be sufficient to replace say the weight of water tanks? Given frame spacing and the fact that batteries might not fill the entire space will the density of weight be sufficient to replace the water and how does one figure that out? Maybe it's irrelevant if the water (or fuel as the case may be) would not weigh anything when the tanks were nearly empty so the batteries will certainly weigh more but at the beginning of a passage, when fuel and water are full, would batteries be the same weight? Lots of variables and it would be pretty boat specific I suppose but maybe Michael could lead us toward how we go about figuring it out?
    The example below has a volume of 0.35 cu.ft. and a weight of 60 lb, so it weighs 2.8 times as much as the same volume of water. You will have to allow for the dead air space around the batteries in your calculation. You could also add some lead plates to fill the dead space. I just grabbed a big one off the list, but the density wont vary much, maybe a little lower on a small one.
    http://www.batteryplex.com/powersonic.cfm

    Model Terminal Volts AH L W H Lbs Price
    PS-12750 NB 12 75 10.25 6.6 8.98 60 $167.99
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  20. #20
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    Default Re: AGM batteries pulling double duty as ballast

    AGM batteries are expensive because they are small and light. I use one in my antique airplane.

    Have you done the arithmetic for the weight you want? Sure, it's great to have sealed units, but if you want 500 lbs worth, that may entail a considerable cost.

  21. #21
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    Default Re: AGM batteries pulling double duty as ballast

    In the example above 75 amp/hours and 60# for $168.00 is not too bad I have not found lead ingots for much less that $2.00/# so we would be looking at $120.00 for lead so ~50% additional cost for 75 amp/hours of power, BUT this would be reoccurring cost every 3-4 years but your not buying fuel so.................

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    Default Re: AGM batteries pulling double duty as ballast

    Quote Originally Posted by eggman918 View Post
    In the example above 75 amp/hours and 60# for $168.00 is not too bad I have not found lead ingots for much less that $2.00/# so we would be looking at $120.00 for lead so ~50% additional cost for 75 amp/hours of power, BUT this would be reoccurring cost every 3-4 years but your not buying fuel so.................
    With care, I've found I can easily get 5 years out of an AGM battery. It depends a lot on the number of charge cycles, of course.
    -Dave

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    Default Re: AGM batteries pulling double duty as ballast

    FWIW--my experience with deep-cycle AGMs in a boat is that they last twice as long as I ever got from flooded cell batts. YMMV.

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

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    Default Re: AGM batteries pulling double duty as ballast

    Skene's Elements of Yacht Design outlines how to calculate C of G for ballast quite well. It is a book well worth having on your bookshelf. As what you are proposing to do is of significant importance to the safety and seaworthiness of your boat, it would be worthwhile to have a trained boat designer do the calculations for your specific boat. It wouldn't cost that much to do, and would be worth every penny to know accurately what the impact of the changes you want done will have on the boat.
    Hope for the best, but plan for the worst.

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    Default Re: AGM batteries pulling double duty as ballast

    While technically correct, Mark0, it really comes down to whether batteries of sufficient power can replace the internal lead ballast wrt mass and still be contained below the sole and have the same (or close) C of G, but not necessarily within the same volume of the lead ballast. For instance, if 600 lb of internal ballast is required and there is room under the sole for 4 cu. ft. of battery-shaped lumps arranged to have the same LCG of the lead ballast, then eggman is good to go. It doesn't matter if the entire hull bottom is covered in batteries where the lead ballast covered only six feet of the hull bottom around midships. (We won't get into weight distribution, radius of gyration, and voltage drop in long cables at this time.)

    At risk of being pedantic, one must not focus on exclusively one problem at a time. Everything on a boat is interconnected, so problems must be solved holistically. The well-worn 'design spiral' approach works well for this. First select a boat design that you wish to build. Determine the C of G of the internal ballast required. Then determine how much power is needed to propel the boat for the desired range. Then select one of the various available battery types and calculate how many are required to deliver that amount of power. Then determine what arrangement of batteries (with lead pigs too, if required) will have a combined C of G equal to the formerly all-lead internal ballast. Now determine if this number of these batteries (and lead pigs) will actually fit in the space available for them. If yes, you are good to go; if not, start back at the top of the spiral and change either the boat design or the battery type and run all the calculations again. And again. And again, until you have either determined a solution, or discovered that it is an intractable problem and you have to move to another design solution. I understand that this is tedious and definitely un-glamorous, but that is boat design in the trenches.
    Hope for the best, but plan for the worst.

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    Default Re: AGM batteries pulling double duty as ballast

    Hi, Yup, I get the design cycle very well. I just thought I'd mention other battery technologies that are most likely a better fit for the application, as the poster did ask what they might be missing/overlooking. I know that many times I get the "design blinders" on, focusing on one option that leads down a single path.
    Cheers,
    Mark

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    Default Re: AGM batteries pulling double duty as ballast

    FWIW, The forklift battery has a density of 162 lb/cu. ft. Flooded cells though, so not so user friendly in a tippy boat.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

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    Default Re: AGM batteries pulling double duty as ballast

    Something nobody has mentioned is that while the designer(s) of whatever inside ballast hull(s) you are looking at have probably chosen a satisfactory method of supporting the lead ballast so that it doesn't spring the planking over time. That method may not be appropriate for battery support. I would want them to be supported by the floor timbers or keel, not by the planking.

    Other than that I think your idea is more than just viable, it's a great idea.
    Last edited by Gib Etheridge; 03-14-2018 at 12:41 AM.

  29. #29
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    Default Re: AGM batteries pulling double duty as ballast

    I have a coupe of AGMs and they feel heavier for their size than traditional lead acids. Does anyone know better?

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    Default Re: AGM batteries pulling double duty as ballast

    Michael, is it safe to put lead pigs down with the batteries? Usually we try to keep all metal out of battery tanks in submarines. If you fasten the batteries down (which you most certainly should) and the lead ingots, is it ok to put them in there with the batteries if the weight is required?
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    Default Re: AGM batteries pulling double duty as ballast

    You tend to get what you pay for in batteries. Better and more costly ones have more lead. AGM is absorbed glass mat, and this refers to the stuff around the lead plates, so it doesn't tell you how much lead is in the cell. As better than average batteries, the average AGM may well have more lead and be heavier than the average wet cell, but that would just be an average.

    When we researched replacing the house batteries in our catamaran about 10 years back, the best bang for the buck was 6 volt golf cart batteries. I don't know if that's still true, but they are made for steady service and to be as long-lived as the type can reasonably be. Set up in pairs to get the 12 volt feed; it works fine. But they do need to be vented and can leak. For the stated purpose here, I like the AGM approach as long as the boat's a good fit for them.
    -Dave

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    Default Re: AGM batteries pulling double duty as ballast

    Sailor, I would isolate the batteries from the lead ballast, but herculean efforts aren't necessary. Standard heavy-duty battery boxes would do.

    Gib, proper seats for the batteries - and lead ballast - would certainly be required. All the stuff of a proper design process.
    Hope for the best, but plan for the worst.

  33. #33
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    Default Re: AGM batteries pulling double duty as ballast

    For sure isolated, I'm picturing strapped down as securely as the batteries. Could they be in the same tank though or should the battery boxes not contain the ingots? I'm not picturing individually boxed batteries but a battery tank similar to how they're done in a diesel electric submarine. Water tight tank with all the battery cells arranged inside it and properly fastened down. Ventilation and any cooling required as well but I doubt a small boat or even a yacht would need cooling for the batteries like we use in our subs. That would just be overkill. I'm also thinking of frame spacing and allowing the batteries to be packed in as tightly as possible given frame spacing and battery size. Clearly a vessel with 6 inch square frames on 16 inch enters won't have golf cart batteries nestled between the frames but ingots could go there while the batteries rest on top of them and under the cabin sole. (Talking much bigger vessel than the OP, sorry for the thread drift eggman)
    If one advances confidently in the direction of his dreams, and endeavors to live the life which he has imagined, he will meet with a success unexpected in common hours.
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  34. #34
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    Default Re: AGM batteries pulling double duty as ballast

    You are asking design-specific questions, Sailor, and we don't know what the design is yet.
    Hope for the best, but plan for the worst.

  35. #35
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    Default Re: AGM batteries pulling double duty as ballast

    I am, you're right. And I'm not sure I'm willing to embarrass myself with the elephant sized bite I've chosen just yet..... Besides, I couldn't go about stealing your livelihood here either so we'll leave it as it is. I'm pretty sure I have a good idea of how I'm going to go about this. I'm just looking for someone who knows best to tell me I'm on the right path.
    If one advances confidently in the direction of his dreams, and endeavors to live the life which he has imagined, he will meet with a success unexpected in common hours.
    -Henry David Thoreau-

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