Cement Ballast - Pros/Cons - SailNet Community

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Old 01-24-2014
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Cement Ballast - Pros/Cons

I'm looking at a boat that is claimed to have a cement ballast. Is this something that should concern me? The boat is a 1987 Com-Pac 23-2

Thank You for any input!
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Old 01-24-2014
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Re: Cement Ballast - Pros/Cons

Cement weighs around 150 lbs. per cu. ft.
Cast iron weighs around 450 lbs. per cu. ft.
Lead weighs around 700 lbs. per c

I'd have to see a profile drawing of the boat showing where the ballast is to make a definitive statement. But consider that there is a very good reason the best boats use lead for ballast.
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Old 01-24-2014
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Re: Cement Ballast - Pros/Cons

Quote:
Originally Posted by Adirondackman View Post
I'm looking at a boat that is claimed to have a cement ballast. Is this something that should concern me? The boat is a 1987 Com-Pac 23-2

Thank You for any input!
As Bob wrote cement is not a good candidate for ballast
Cement weighs around 150 lbs. per cu. ft.
Water weighs around 60 lbs. per cu. ft.

In the some early GRP production boats they used cement mixed with scrap iron as internal ballast in an encapsulated keel.

Some of these boats suffer from "keel sickness", the iron inside the cement has rusted so badly that the encapsulated keel starts to expand.
The keel starts to loose its shape and in some cases open up.

Replacing the internal ballast with a construction like this is no fun.
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Old 01-24-2014
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Re: Cement Ballast - Pros/Cons

"keel sickness" hehe - never heard of that, but your explanation makes absolute sense...
not everybody knows that rusted iron increases in volume by the factor of ~3 but it also gets heavier...
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Old 01-24-2014
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Re: Cement Ballast - Pros/Cons

While there have been a number of boats which have had cement ballast, there is nothing good about cement ballast and if that is really the case it would normally be a deal breaker for me.

As Bob Perry pointed out there is a big difference in density between a proper lead ballast and the usually mix of steel and concrete that is typically referred to as 'concrete ballast'. The low density of that mixture (appoximately half of lead) means that it is harder to get the ballast as low in the boat as would be the case with lead ballast which usually results in some mix of a wider and/or longer encapsulation envelope inducing greater drag, more draft than might be required by a denser ballast, or less stability. The greater drag and the lesser stability result in measurably reduced performance over a normal encasulated keel, and even greater reduction over an external, bolted-on cast lead (or even iron) ballast.

Beyond the performance issues of low density ballast, there are serious issues from a quality control and from long term durability and maintainability issues that would concern me. To explain, normally when people talk about 'concrete ballast', that more typically refers to concrete with scrap steel mixed in. The scrap steel is normally in the form of 'boiler punchings' which has come to be used as a generic shorthand term for small pieces of scrap steel produced in various manufacturing processes.

In the best case, the steel is carefully weighed and the concrete carefully mixed so that the ballast is of a uniform weight from boat to boat and the steel is uniformly distributed through the matrix. What more typically happens is that the steel is added 'by eye' and so the ballast can vary in weight pretty dramatically, and the steel can be located assymentrically in all directions.

Using best practices, the ballast is cast out side of the fiberglass keel encapsulation envelope allowing the concrete to cure (and shrink) before being inserted into the keel encapsulation envelope. Then the encapsulation envelope is generously filled with a slurry that is a mix of resin and a thickening agent and the ballast casting set into place. Once the slurry sets, the top of the concrete is carefully glassed over to a thickness that is close to the hull thickness. Lastly transverse framing is added over the top to stiffen the joint between the keel and the hull.

That is rarely done. Often the concrete is cast in the hull mold. Most times a light membrane is added over the top of the concrete and that is it. The problem is with these items are that when concrete is poured and cures, it shrinks, pulling away from the mould, which in this case is the encapsulation envelope. Instead of a watertight bond between the concrete and glass, there is a small but perfect capillary to allow water/moisture to move around the casting. Once moisture gets into the encapsulation envelope the steel in the ballast can begin to rust and pry apart the concrete matrix, shattering it into small pieces. (I once helped a fellow dig out all of the ballast from a Buccaneer which had disintegrated. We removed pieces of damp rusty concrete that were as large as 3-4 inches and as small as sand.)

And in most cases, unless the boat is built extremely well, water does eventually get into the encapsulation envelope. It gets in by a number of routes. In the case of the Buccaneer that I mentioned above, we concluded that the boat apparently had a minor grounding. It was a grounding which did not pierce the encapsulation envelope, but it did cause enough of an impact that, in the absense of a heavy enough membrane and/or transverse framing, there was adequate deflection to cause the ballast to push up through the membrane above the ballast. It only made a small slice in the glass, but it was enough to allow bilge water to seep into the encapsulation and rust out the steel, and blow the concrete apart.

But water can also get in from the bottom if the encapsulation envelope is pierced in a grounding. Once water gets in there, its almost impossible to get out again since the concrete will absorb the water like a sponge. And that moisture not only attacks the steel in the ballast, it also can attack the fiberglass. One of the surprises on the Buccaneer was that the fiberglass was badly blistered in the interior of the encapsulation envelope.

But beyond these issues is a bigger one in my mind. Concrete ballast is only used as a cost savings measure since there is no good reason to use Concrete ballast except to save money. And when I see a manufacturer electing to use concrete in the matrix, I always am suspicious of the overall quality of the boat thinking that, if a manufacturer chose to cut this large corner, I wonder what other, less obvious corners were cut in the process.

I should note that I am a little surprised that Hutchins who built the Compacts used concrete ballast. I have always perceived them as being a better builder than that. Hutchins is still in business and you might want to contact them to discuss how these boats were built in more detail.

Respectfully,
Jeff
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Re: Cement Ballast - Pros/Cons

My Cheoy Lee 31' offshore ketch had concrete over cast iron ballast, with no issues after 45 years.
I have to say that the motion of that boat was the most comfortable of any sailboat I've ever been on.
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Re: Cement Ballast - Pros/Cons

Compac sailboats by Hutchins Company is a well built boat and the numbers that are still around can attest to that. I am restoring a compact 16 as I write this and from everything I have read as well as confirmation from Hutchins the 16 has lead pellets for its ballast and a cement cap is poured over it with a layer of fiberglass over that. There is a strong forum for compac sailboats at:

Com-Pac Yacht Owners Association - Index
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Re: Cement Ballast - Pros/Cons

Quote:
Originally Posted by waterwks4me View Post
Compac sailboats by Hutchins Company is a well built boat and the numbers that are still around can attest to that. I am restoring a compact 16 as I write this and from everything I have read as well as confirmation from Hutchins the 16 has lead pellets for its ballast and a cement cap is poured over it with a layer of fiberglass over that. There is a strong forum for compac sailboats at:

Com-Pac Yacht Owners Association - Index
Perceptions like yours were precisely why I suggested that the OP contact Hutchins to hear it direct from horse's mouth. My sense is that the Com-pacs were simply but reasonably well constructed.

Assuming your description is acurate, certainly lead pellets in concrete is a better solution than iron in concrete. But even so, your description still does not answer the other questions about whether the concrete was cast inside the hull or in a separate mold, whether the lead pellets were mixed with the concrete (better) or poured in the hull cement cap is poured over it (which is a pretty poor way to do it), whether the fiberglass sealer membrane is structural of only a thin separator to keep water out and so on.

Jeff
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Re: Cement Ballast - Pros/Cons

Last month near Tampa we rented kayaks to go see manatees and we needed an anchor. The rental lady got out a gallon water jug and effectively said "this is heavy, use this as your anchor".

I explained that no, a container of water would not make a good anchor. Seeing this thread about concrete reminded me of this. Concrete "partially floats" in water.

One of our on-the-hard boat neighbors is re-doing his concrete keel. As Jeff mentioned, there was only a thin layer of fiberglass over it. If the boat ever capsized, the ballast would drop down into in the salon. That would be the end of it.

Regards,
Brad
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Re: Cement Ballast - Pros/Cons

Island Packet uses a layer of concrete in it's ballast, not exactly confidence inspiring. It is separated from the metal ballast (I believe depending on year can be lead or iron) by a layer of epoxy. I think in a Compac 23 if used in sheltered waters should be fine. I would not want to take it out in the open ocean. If it is over lead that should be fine, but if over iorn I would be worried about corrosion as Concrete holds a lot of moisture, especially if not separated by some epoxy.
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