This looks similiar to what we have. If so it is an old Hood
Sea Furl Mark II. This was one of the first genertion furlers that had two sail slots not for changing sails
but to allow flying twin head sails
wing and wing. I think I still have the owners manual but may have to dig deep for it. The spring was used to keep tension between the foil sections and upper furler
bearing. One draw back of this earilir version is you can not tighten the halyard
drum tight like you can with todays furlers. If you overtighten the halyard
the furler will jam up and work hard. I last rebuilt ours about 10 years ago and for crusing works surprisingly well.