I would really be interested in how your friend rigs the boat for fishing. I believe you said he trolls. I can see blocks located in a high position both fore & aft but I don’t intuitively see how they would be reeved for fishing. Photos & his verbal description would be great.
As for a model, research the various hull manufacturers for something that is close to the Cygnus 21. Alter it as necessary & then build away!
Very interesting subject.

I have gone through the search function on the website for references of a Cygnus 21 . There are posts from 10 years ago of the 33’ Cygnus but none on the 21’ version of this inshore fishing vessel.

I have seen it in YouTube videos but none reference to a kit.

“Cygnus GM21
Cygnus Marine, Britain’s leading GRP fishing and workboat builders, first introduced this design in 1977, and since that date the CYGNUS GM21 has become the accepted standard for inshore fishing vessels, with over 300 craft being constructed.” From the Cygnus company website.

The fisherman, Jimmy, who works and lives out on an island of the Shetlands, has one of these. He fishes by himself during lobster season. Or with two if fish closer to the rocks. Note that his vessel is fitted with a bow thruster just for that purpose.

Does anyone know of a model for the small fishing vessel?