'Fraid not. Even if you have the certificate, the only information available is the length and number of hulls.
Not sure that is quite true. When I bought my boat it was registered under SSR. I spoke to Swansea who were able to tell me the name and contact details of the original owner (not the person who sold it to me). I knew the boat details of course so not certain what info they used, as the name had been changed.
Yes, the SSR Registry has some details but it's not publicly searchable, unlike the radio licence database. You can get (for £46) a Transcript of SSR registration, but that won't show the builder or model name, and will I think have the owner details redacted. Even Part I registration will not show the model though it will give the builder's name and the owners's details.
Nope. The hatch on the 21 had an oval (ish) shape with the top raised. Yes to bilge or fin. But the bilge keels weren't like that. I have the original drawings....
I thought so too when I first saw her, but she has a counter stern and inboard-mounted rudder, whereas the Cox has a transom -hung rudder (no sign of alteration of moulding). The stem is a continuous curve from forefoot to stemhead, where the Cox has a much straighter stem. Overall, she has much more rocker along the centreline, making the hull much deeper amidships and giving her a bit of a "pot-bellied" look. The keels are laughably un-hydrodynamic: make the ones on Macwesters look sleek! The deck moulding is VERY close to the one on the Cox, except that the main bulkhead is convex, curving outwards into the cockpit whereas the Cox has a concave bulkhead. I did wonder if this was another boat by the same designer / builder, but most likely to be a small production run of mouldings only, for home completion.
The deck moulding is very similar to the Cox, but the hull is entirely different. Looks much more like Robert Tucker: almost like a Corribee on steroids.
A cheap boat is better than none...And, some of the ugly bits are under the water, out of sight..