Hello Andy,
That's an interesting observation about Sarik's 'Katie'. I took a look on their website and I agree with you, the shape of the GRP hull and the sail plan both look very similar. Looking at the hull dimensions, they quote 33cm beam which matches my model and 103cm length. My hull is 102cm long - slightly less but not much.
My hull was supplied by Mike Mayhew of Waverley models in Clevedon, and the GRP is a yellowish colour inside. Sarik's Katie hull appears to be white. The name 'Dyarchy' was handwritten inside the hull when I obtained it. I believe that Mike Mayhew and David Alderton were not on good terms at that time either, so I very much doubt that Mike obtained the GRP hull from David.
I also tried to research 'Dyarchy' at the time I was building this one. All I could find were these two entries on
www.woodenboatvb.com:
(1) "The "Original" 41 foot Dyarchy was indeed a Bristol Channel Pilot Cutter - built in 1901 at Pill by Cooper. In 1937, her owner commisioned Laurent Giles to design him a new boat - and the name "Dyarchy" was carried on to this new design, which is one of the finest examples of modern gaff-rigged sailing craft. The original BCPC was broken up and no longer exists."
(2) "Most of the original Bristol Channel Pilot cutters were typically in the 49 foot + range on deck. A few smaller boats with transom sterns were built as well. One typical of this smaller version was the 38 foot 'Dyarchy' built by Cooper at Pill in 1901. The boat has long since gone, but you can still buy 'study-plans' for it from the Greenwich Maritime Museum in the UK (they also have a website -try a search). These are only sufficient to build models from though."
Based on this I believed that my model's hull was indeed based on the 'Dyarchy', one of the shorter transom-stern pilot cutters described above. From the 102cm length of my hull and a scale of 1:12, the original would have been 40' and 2", which lies in the range quoted above for the original.