Join Date: Feb 2000
Location: Annapolis, Md
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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.
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Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay