As you can see from this old Surf N Sport ad, performance was the game.. Thrusters, quads, and my favorite, twins..
Here's the classic performance twin that I have been shaping for over 30 years..
Backside 360 on a tools twinnie circa 80'
4 built for fun..
Classic twins are typically wider throughout, shorter, and use wider base keel. Modern twins have a pulled in nose, tighter tail and a taller, narrower base keel with a tad more rake. The idea on the modern twins is to keep the feel loose while opening up the possibility of approaching more waves and more angles..
I rode this board 24 years ago on my honeymoon at Honalua bay in solid 8' -10' surf.. 2.5 fins..