Koopman's Design. The toe rail seems to indicate that the boat might be aluminum built and not steel.
The weight too (7T) so maybe you are right but the boat is advertised for steel boat. Also the tankage is typical of a fast and light boat, not of an heavier steel cruiser.
If it is the case and the add is wrong then they are pretty dumb because a 30 year old aluminum boat has a market value bigger than a steel one.
Koopmans 37 YEAR 1984, MATERIAL Steel. In German is also advertised as a steel boat:
"Robuste Stahlyacht mit Teakdeck und hervorragenden Segeleigenschaften.
Für sicheres und komfortables Reisen auf See."
Here you have what looks like the same design (also steel) but without teak. Here they give some more details:
"Sailingyacht Koopmans 37 "Vita Nova", built in 1979/1980 by Huizer Marina - Holland, dim.: 11,45 (lwl 9.50) x 3.37 x 2.00 m, headway approx. 18 m, designed by Dick Koopmans sr, steel hull, wood epoxy superstructure and deck, teak cockpit, Moonlight hardened glass windows in aluminium framing (2000), round bilged blue hull with white striping, fin keel, displacement approx. 10 tonnes, ballast approx. 3,3 tonnes (lead), fuel tank approx. 120 litres (steel), fresh water tank approx. 2x 150 litres in GRP tanks, tiller steering, emergency tiller."
So it seems that on the first boat they have the weight wrong or the material wrong. 10T is good for a steel boat and a lot more credible than 7T. However it seems that this one has the same type of toe rail, if not the same. Maybe because the deck is not steel?
Anyway Koopmans used to make the same design in steel and aluminium (with the needed structural alterations) so it is possible that the weight is right and that the first one is an aluminium version.
I think the boat is this one:
That later evolved to this nicer and more modern hull;