Water filled Keel tanks?

I have two 400/400 gallons tanks in the keel, which are sealed and flooded with water. It's been like this possibly over a decade. I believe they are steel tanks, since they are part of the keel.
If I wish to revive these tanks and use them again, what would be the cleanup process? Anyone ever had to do this?

Your first task is to gain access to the insides of the tanks. Any inspection ports? If not can you construct them?

Must be a reason they were sealed. Are they ballast? Once you empty them check stability and roll resistance.

I've never seen a flooded keel that was used as 'usable' water tankage. I've only ever seen these used for ballast.

I've never seen a 'sealed' flooded keel. All the ones I've seen have open ports and usually fill through displacement when launched and drain when hauled.

I wouldn't want to see a flooded keel that is only half-full. I would think it would adversely impact handling by introducing a 'Slack Tank' effect.

D.Duck44 said:

Your first task is to gain access to the insides of the tanks. Any inspection ports? If not can you construct them?

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No, I don't see any ports. Only pipes sealed.
I don't think there is a way to install a reasonably sized port.

bayview said:

Must be a reason they were sealed. Are they ballast? Once you empty them check stability and roll resistance.

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The boat was built originally as a long range cruiser. The original document shows 1600 gallons fuel capacity.
I suspect, it is functioning as a ballast now. Nobody knows, why they were flooded with water? The boat was used as a livea-board for more then a decade.
I'd like to put it back as a long range cruiser and have all the 1600 gallons available.

Shrew said:

I've never seen a flooded keel that was used as 'usable' water tankage. I've only ever seen these used for ballast..

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It is not the keel what is flooded. The two tanks are, which are built into the keel. The keel is a ' box keel ' and kind of flat at the bottom.

Some photos might help the tank discussion.

Also, hard to understand why a keel would be open to the bottom. Surely it would quickly fill up with slime and sea creatures, and really stink when on the hard??

Chrisjs said:

Some photos might help the tank discussion.

Also, hard to understand why a keel would be open to the bottom. Surely it would quickly fill up with slime and sea creatures, and really stink when on the hard??

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I never said that the keel was open to the bottom. The keel has two tanks incorporated on each side. The pipe from each tank comes up to the ER.

I will take better pictures tonight, when I go there. Here is one, where you could see the pipe's end sealed.

To use the tanks for fuel, you need to get all the water out. Hard to do without a inspection plate. You could use a fiberoptic camera to inspect thru the fill ports. I wouldn't pump the water out, add fuel and hope my filters would catch all the water. Besides, water left in sealed tanks grows things. In sailing ships, drinking water in barrels turned green in a couple months.

If the tanks are part of the hull, it might be best, when hauled, to cut holes in the hull. You could add flush mount access ports. Then you could clean and sand blast if necessary. Even add a tank coating. I have 75 year old mild steel fuel tanks, still doing their job, but never used for water storage.

Lepke said:

To use the tanks for fuel, you need to get all the water out. Hard to do without a inspection plate. You could use a fiberoptic camera to inspect thru the fill ports. I wouldn't pump the water out, add fuel and hope my filters would catch all the water. Besides, water left in sealed tanks grows things. In sailing ships, drinking water in barrels turned green in a couple months.

If the tanks are part of the hull, it might be best, when hauled, to cut holes in the hull. You could add flush mount access ports. Then you could clean and sand blast if necessary. Even add a tank coating. I have 75 year old mild steel fuel tanks, still doing their job, but never used for water storage.

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If I understand you correctly, you would get as much water out as possible and fill it up with fuel. Let the fuel flow and use filters to catch the water and the other stuff. Is this correct?
I thought about a primitive polishing solution with a pump and large filters just to circulate the fuel in each tank. It could be a permanent installation and continuous run. I have seen people building these. This could eliminate the junk inside the tanks, in time. This job is not urgent, so more brainstorming is possible on the subject.

I will haul it out this December and I will see the options for opening the tanks from the hull side. Perhaps, it could be a project for the future?

These tanks were not flooded for water storage/use. I think it was just a decision for buoyancy and not dealing with those tanks. The other 2 tanks with 800 gallons is enough for most of the people here in PNW.

First off...sailboats have had fuel and water tanks in their keels for many years and many brands. The first that comes to mind if Gulfstar, and all of their boats have fiberglass tanks integral with the keel...sail or power. Islander is another with metal fuel tanks in the keel.

Second, with that much tankage that low in the keel, I can easily imagine flooding it with water to keep the boat within designed stability parameters. That's 5,600 pounds of diesel, when full. My grandads had told me "back in the day" they would trim out the ship as it burned "oil" by flooding the tanks with sea water. Of course old war stories followed booze

Personally, I'd install inspection ports and steam clean them after draining like you would any old tank and have them inspected. If they aren't rotten, I'd use them. Install 2 filters per tank (primary and bypass) and tie it into your fuel manifold. IF, IF, IF they are problematic with clogs after running them...then look at replacing them.

My 2 cents that you didn't pay for, lol.

cool beans said:

Personally, I'd install inspection ports and steam clean them after draining like you would any old tank and have them inspected. If they aren't rotten, I'd use them. Install 2 filters per tank (primary and bypass) and tie it into your fuel manifold. IF, IF, IF they are problematic with clogs after running them...then look at replacing them.
My 2 cents that you didn't pay for, lol.

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Have I mentioned that this is a sailboat hull by design?

I think that is a pretty good plan. Since, there is no urgency, I can plan this out well and get it done, before I really need 1600 gallons.

Where do you want me to mail the 2 cents? Lol

more photos

I took some yesterday. You can see pipes are sticking up, sealed. The wide ones should be the fill up pipes. I don't know what the smaller ones are for?
Unfortunately, there is a 20g waterheater is sitting on the top of this area, so it is hard to take good pictures. I hope you can see the tanks' top?

Those are pipe plugs, so those are tanks intended for something probably fuel. I would start by removing pugs and pumping the water into a container to see if it has a fuel smell or any oil appears if you carefully pump from the surface of the water.
Pumping through a boat diaper might show fuel as well.

Pipe plugged port is probably for sounding tank. It could also be a discontinued vent when PO decided to use tanks as ballast instead of fuel tank. If it was a vent, it would have continued up to deck level or higher by pipe or hose.

I would have pumped those tanks dry before haulout,if they are water ballast.

LeoKa said:

Have I mentioned that this is a sailboat hull by design?

I think that is a pretty good plan. Since, there is no urgency, I can plan this out well and get it done, before I really need 1600 gallons.

Where do you want me to mail the 2 cents? Lol

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PayPal works. 2 cents plus a $35 consultation fee and a $25 "convenience" fee totals to $60.02

:lol:

Those would scare me to death! Are they integral with the hull? I'd fear they were quietly corroding themselves to dangerous. I would not be happy with them until I knew they were not dangerously corroded and for evermore verifiably not corroded at all.


I suppose the less squeamish would be less concerned with a water tank open to the sea as long as the tank top and connections were intact. But not me!

DHeckrotte said:

Those would scare me to death! Are they integral with the hull? I'd fear they were quietly corroding themselves to dangerous. I would not be happy with them until I knew they were not dangerously corroded and for evermore verifiably not corroded at all.

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Would it still corrode, if it was airtight and full with water?
I don't even know what water is in there? It could be salt water.

If I understand you correctly, you don't recommend to open these tank from below. No inspection hole from the hull?

Well, it's true that water-filled heating systems don't corrode very quickly and don't suffer from mixing steel and copper elements. No oxygen. I presume that the oxygen in the newly-filled system corrodes the iron that it can and then it's used up until the next draining, repair, and refilling.


Your boat's steel, it can be cut and welded. I don't imagine that there's any reason why you shouldn't work from the most reasonably available, comfortable place.


I doubt that your PO would have filled the tanks with salt water. Too much trouble / too easy to run a hose.


You will have to be able to verify that the newly-cleaned tank, newly filled with diesel, remains free of water and, particularly, does not either contaminate the sea by leaking, nor supply your filter/engine with salt water.

DHeckrotte said:

Your boat's steel, it can be cut and welded. I don't imagine that there's any reason why you shouldn't work from the most reasonably available, comfortable place.

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I am confused. In your previous comment you said that opening the tanks towards seawater, from below, is not a good idea.
I this comment, you say that work from the most comfortable direction. Are you referring to the idea to have inspection ports installed from below?
I don't see any way to do it from the ER, from the top.

First post suggested how bad it might be if the tanks had corroded through from the inside and opened the contents to sea water. They surely cannot be, or have been, painted/protected from the inside without huge mechanically-fastened access ports. Welding would have burned the paint or galvanizing off along the welded seam.


Second post suggests that you work from a place of comfort. You can control the corrosion from outside and perhaps, with adequate sized access, control - or at least monitor - corrosion from the inside.

I remember Ironsides from years ago. A lot of work was done to try and correct some issues. One of those issues was stability. I wouldn't be surprised that those tanks were filled and sealed to increase displacement and help with stability. If you are going to make those tanks active, they could, at some point, be empty. Before I did that I'd want to understand what was going on initially with filling and sealing them and if you are going to use them what effect potentially running with them empty might have

LeoKa said:

I have two 400/400 gallons tanks in the keel, which are sealed and flooded with water. It's been like this possibly over a decade. I believe they are steel tanks, since they are part of the keel.
If I wish to revive these tanks and use them again, what would be the cleanup process? Anyone ever had to do this?

Click to expand...

OK - well - who knew? I know that variable ballast is used on larger vessels, but have not seen it in smaller vessels. There are few things you should look at.

First, if they are sealed and still full that's good. If there had been a leak and they are no longer full the can affect the stability and safety of the vessel.

When they were filled and sealed, I don't know what protocol was in place at that time to keep the water safe. Any air and you have the potential for chemical changes. I think a good example is homes that get mold and require remediation. If you have an issue with these tanks a pro should handle it.

If you feel they may be compromised make sure the hull and surroundings are inspected for damage to make sure nothing is compromised.

Going forward, I'd make modifications to be able to maintain those tanks - by that I mean to refill and seal them with proper chemical treatment - not have variable ballast.

Just a few observations.

markajh said:

OK - well - who knew? I know that variable ballast is used on larger vessels, but have not seen it in smaller vessels. There are few things you should look at.
Going forward, I'd make modifications to be able to maintain those tanks - by that I mean to refill and seal them with proper chemical treatment - not have variable ballast..

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Yes, the goal is to know the state of the tanks. I don't have any issues with them for now. I plan to utilize them again as fuel tanks in the future.
I will do inspection at the next haul out. Maybe next year, an inspection port, too.

What do you mean by variable ballast?

Won`t the boat handle differently depending on the quantity of fuel in the keel fuel tanks? How to compensate for that varying degree of stability?
Sailboats have their counterbalancing ballast weight in the keel and don`t do well on stability if the keel falls off. Partly water entry, but largely due to loss of designed stability,they fall over.

BruceK said:

Won`t the boat handle differently depending on the quantity of fuel in the keel fuel tanks? How to compensate for that varying degree of stability?

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Someone did suggest to me to add more lead, if I remove the water. Even if I fill it up with diesel, since it is lighter than water.

The whole concept seems strange to me. Maybe if you want to check the integrity of the tanks, you could hire an ultrasound contractor or buy an ultrasound.
Grainger has one for $368 approx.
Ultrasonic Thickness Gauge

• Item # 161F01
• Mfr. Model # TM-8811
• Catalog Page # N/A
• UNSPSC # 41111623

D.Duck44 said:

The whole concept seems strange to me.
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Which concept?
Using it as a fuel tank, or flooding it with water for ballast?
Again, the PO wanted no fuel tank in the keel. The existing 2x400 tank in the ER was enough for them. I am trying to figure out how to bring the keel tanks back to being fuel tanks again.