Seem to have been reading a lot lately about keels falling off/ cracking hulls and generally giving grief. Why did one-piece boats go out of fashion?
Is it that you can't make modern keel profiles in this way? Is it just cheaper to bolt on an iron keel or two? Encapsulated ballast can have it's own problems but such a design does seem a lot less likely to be the cause of catastrophic flooding or a sudden and permanent inversion.
I had encapsulated keels on my first boat - a Vivacity 20 (aka, unkindly, a Viscosity). I thought at one stage that I had water coming up them following damage to the bottom of the keels (several seasons of banging down on hard sand with embedded chuckies). In the process of investigation I dug out the top inch or so of the ballast: oval steel punchings - the holes, I reckoned, from Dexion strips - set in some kind of bitumen. What was impressive was that until being disturbed the punchings were completely rust free: they had obviously been completely air sealed. Within a few hours of exposing them surface rust appeared. The source of the water ingress proved to have nothing to do with the keels, but that's another story.
I recently read suggestions that this type of construction is vulnerable if water leaks in through cracks making the punchings rust and swell, bursting open the GRP. I would say from my experience that, providing sufficient bedding material was used, i.e. no voids, then there is no reason why significant rusting of the punchings should occur. My keel bottoms were cracked and letting in water to the bottom of the ballast but it got no further, and there was absolutely no sign of swelling. (I repaired / replaced the GRP keel "shoes" which was fairly straightforward after working out how to hold the boat up to give access... )
I don't know why it's a construction that's gone out of fashion. Perhaps with the increasing incidence of high tech keels falling off it might well come back!
