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  #1  
Old 10-03-2008
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Question batteries under cabin sole

On the Cape Dory web site Ive been kicking around the idea of keeping batteries under the cabin sole in a largish bilge area on my CD. Seems the general concensus is that in a flood, the batteries would short and leave one with no bilge pump power (among other power needing things too). Also if one had lead/acid batteries (non gell or AGM) the contact of seawater and acid would produce a dangerous gas(es). (I have AGMs and so wasnt worried about the gas aspect as much)
I was wondering if anybody over here at Sailnet has any differing ideas or solutions which might address these concerns. I thought Id seen lots of batteries under the sole over the years but maybe it was just a wishful memory or if true, a bad idea.
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I don't know how feasible this would be but you might be able to coat the terminals to make them watertight so that in a flood they don't short.

Just a thought.
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Yes, you probably have seen a lot of batteries under cabin soles...since that is a pretty typical location for them. Batteries, due to their weight really need to be kept low in the boat... and it is very difficult to keep them both low in the boat and out of the bilges... even under the settees isn't an ideal situation, especially on a smaller sailboat.

If you have AGMs, it might be possible to seal the terminals, but that might cause maintenance and safety problems.


BTW, you really shouldn't have only electric bilge pumps. Ideally, you should have two really stinking big manual bilge pumps—one that is mounted so it can be operated from the cockpit, and the other setup so that it can be operated from inside the cabin, with the boat all closed up.
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Old 10-03-2008
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Hey, scosh. There are some real issues but I think they are manageable ones.

Yes, when seawater mixes with battery acid, free chlorine gas is given off and it will burns your lungs and eyes out in fast order. A Very Bad Thing.

Since you have AGMs that should not be an issue.

On the other hand, any flooding with salt water would short the batteries out and you would have some--limited--power left while they shorted out. No one seems sure about how much current will pass, I supposed you could take a battery to the shore, submerge it, and see.

But I think you could prevent this by carefully cleaning and mounting your battery terminals, then thoroughly potting them with "Liquid Lectric" or a similar vinyl coating. I've potted battery terminals on wet lead batteries that way for ages, to prevent corrosion. Done neatly with 4-5 coats of the stuff and it lasts at least five years. After it has thoroughly dried, I supposed you could also liberally apply some silicon grease (aka high-dielectric grease, aka brake grease--cheapest source of it, in 4-8 ounce tubes). That's all it takes to keep out seawater really, some generous non-migrating grease.

And since your batteries will be close to the bilge pump one could argue they will power it for longer, faster, too.[g]

With AGMs and *top* quality installation, I see no problem there.
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I have one electric pump down in the bilge and one manual working from the cockpit. I like your recommendation to also have a manual one inside the cabin too but Im not sure if Im soloing I could use both at once.
So, what does everyone think about the shorting issue when flooded? Seems possible or likely? And all these boats with batteries that weve seen under the sole are just unaware or playing the odds? Am I worrying about something that is rare enough to ignore considering the benefits of the low batteries?
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Quote:
Originally Posted by sailingdog View Post
BTW, you really shouldn't have only electric bilge pumps. Ideally, you should have two really stinking big manual bilge pumps
And two really stinking big deck hands to man them
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The point isn't that you can man both of them, though if you have crew and the water is filling the cabin... both would probably be in use.

The reason is if you have to be inside the boat for any reason—it is blowing 80 mph... there's golf-ball sized hail, etc—you can still pump out the bilge—which isn't possible if the only high-capacity bilge pump is only in the cockpit.

Likewise, if the only high-capacity manual pump you've got is in the cabin, and you need to be sailing the boat—say trying to claw off a lee shore that is going to kill you—you can still be pumping out the boat and helping the electrical ones out...

From what I've seen, a good high-capacity manual bilge pump beats most of the electric bilge pumps by an order of magnitude. For instance, a Whale Mk V, which isn't the highest capacity manual diaphragm bilge pump, does about 15 gallons per minute, or 900 GPH... with up to about a 15' head. A really high capacity electric bilge pump, like a Rule 3700 won't do much more than that if you've got any sort of head on it—as the 3700 GPH rating is for ZERO HEAD—and if you've got it in the bottom of the bilge and it has to pump it up six or seven feet to the top of the anti-siphon loop before it goes out the through-hull, it's probably only doing about 900-1200 GPH, but eating serious amps to do it.

BTW, the reason I compared the Rule 3700 with the Whale Mk V is that both use a 1.5" diameter hose, so should be roughly comparable in capacity, in theory.

Quote:
Originally Posted by scosch View Post
I have one electric pump down in the bilge and one manual working from the cockpit. I like your recommendation to also have a manual one inside the cabin too but Im not sure if Im soloing I could use both at once.
So, what does everyone think about the shorting issue when flooded? Seems possible or likely? And all these boats with batteries that weve seen under the sole are just unaware or playing the odds? Am I worrying about something that is rare enough to ignore considering the benefits of the low batteries?
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While we may be drifting abit from my original question, as long as were talking about relatively unlikely events, seems like a warning alarm for rising water in the bilge might help one to take notice before the batteries became submerged. Do they exist and has anyone bothered with them?
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Not sure how you'd do that. I guess you could wire it with a float switch.

Of course you'd have to take the heel into account.
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You can purchase an inexpensive water alarm at most hardware stores. They run on a small battery and are designed for use in basements at or near hot water tanks.

My batteries are under a berth and the water would have to be quite high before they would get wet. I really don't think that you could seal the teminals well enough to keep them away from salt water. I think that in a few monthes the two materials, the battery casing and the sealant, would seperate. Seperation would occur because the materials are different and they expand at different rates. Just my opinion. I have not done any testing.

Paul
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