Firstly, it's unbraked. What are people's views on the braked/unbraked issue?
Secondly, the trailer has a breakback mechanism which the current owner has never used. Was there a standard trailer for the Sea hawk, our do they vary a lot?
Can anyone shed any light on Puffin's past, particularly with reference to the trailer?
My understanding is that as the weight of the SeaHawk is above that which would be allowed on the road with an unbraked trailer, therefore what you have there is suitable only for manoeuvring around a marina or boatyard.
The main source of information about SeaHawk trailers can be found here:
http://www.seahawk17.org.uk/boatshed/trailers.htm but in summary, there was no standard trailer for a SeaHawk, though one purpose built type predominated. However, most of those will have rotted away by now, so there's nothing that can be considered standard these days.
I have never used a break-back trailer. Personally, my favourite type for a guy who always aspired to travel round the country to different waters is the design illustrated in the a video in a post about Amigo, a Pedro, but the hulls are the same. I have further photos that show the yard/launching trolley separately and mounted piggy-back on the road trailer.
All I know of about Puffin can be gleaned by following the link in the advert and then searching for the various previous names.
I agree with Greg about the weight being over the maximum 750kg allowed with unbraked trailers. My own boat was a 17' Pirate not a Seahawk but is a very similar boat. It came with a 'purpose built ' trailer with tyres and suspension units which limited the max weight to 750kg although it was a braked trailer. I towed it home and it towed well. Then I took it to a weighbridge and found it and the trailer came to 970kg! I had to replace the axle and the tyres to achieve 1000kg. Maybe a trip to a weighbridge to find out the weight you have with your boat would be a good idea and help with correct choice of trailer.