ok I'll bite why you? and how do you come to know so much about the southwind brand?
If someone knows & has already posted it, I give the short version......
It seems from reading all the posts on here that most of you have just discovered these Tunnels. I gave a hint on my first posts about the Berkley Advertisement. It's the name of the driver of the World Record. It's the history of how they came to be sold and how they progressed till they kind of went away. Also why others copied that bottom. And also a little twist on the bottom that, I'm sure no one knows, and it has to do with one of the boats on that poster.....
This one..

I got to ride in this boat. Talk about an E ticket! It was a Tunnel, but it had modifications, the only one Southwind built! I was at Buena Vista one day and this boat pulled in. I was wiping down mine and he came over to me......we chatted for awhile and the rest is history...
I'll try to explaine the mods. The biggest one was the jet "placement".
When I walked up to it, the first thing I saw was that the jet extension had been cut off and the jet was flush with the back of the hull. When I asked about the change, he told me because the cav plates were fixed, they wanted to get the nose higher in the air in order to get more speed, less friction. (sidebar...I have seen, & have a pic somewhere, of a Tunnel with footpetal, v-drive type ajustable cav plate)...The other mod was

?. I may have to draw this to explaine it. There is a tunnel on each side of the jet. On the outside & bottom edge of the tunnel, they had incorperated a 1" x 1" piece about 2' long, looked like a C, to help channel the water & keep the rear of the boat glued to the water. It worked, an E ticket ride...