Fond memories of diving around the North Antrim coast from a Humber Alpha, whilst we normally used it with just 4 divers we have had 6 with twin sets in one, powered by an old 55 hp mariner. It would plane with 4 divers about 22 knots but not with 6. They have bigger tubes than other ribs in there class which helps carry the load. Only a medium V hull but that never stopped us. Could be towed by anything and hand launched across sand. We even dragged one 100 yards across mud one Sunday rather than wait for the tide to come back in. It would slam but we just slowed down a bit tofind a comfortable speed.
Not a bad price especially if he will take an offer just before Xmas, but i would ditch the frame thats doing nothing for the boat.
Ribnet is best viewed on a computer of some sort