Old Guy Tom
Bang on the money, these deck fixtures are almost as old as sailing and the term 'Horse' comes from English late middle ages when they were constructed from heavy timber, it was called a horse simply because of its likeness to a carpenters saw horse, which itself was called saw horse because it four legs and a strong back.
I found this out many years ago, I had taken my Hillyard into Dickies on the Menai Straights, as it was a timber boat it attracted the attention of many people including an old boatbuilder who, over the next few days and during many convivial pints taught me more about timber boat construction then I could have ever have learnt in a classroom.
Happy days
Paul