Shortened rail-length longboard (DESIGN THREAD)

Sure, both of those will work.   If you can find the right conditions for them.   

OK, and would an 8’4 length also work same profile?

The 84SP rocker is nearly identical to what they show for the 9’0", just scaled up

You should always plan to get a couple inches less length than the blank.  The ends of the blanks sometimes get bumped and they usually don’t have exactly the rail shape you’re looking for.  

yep, got it. i’ll work on an blueprint next and post it here soon

I had a chance to see Devon Howard in a very good solid swell here in Hawaii. He is very good, very smooth beautiful style. He rode a midlength on the biggest day and a log when it came down.

The comment about foot placement is spot on. I ride a lot of midlengths and that is exactly what I’ve noticed, You tend to use the front foot as the anchor and the back foot goes up or back depending on how sharp you want to make your turn. Feet closer together, pushing together for the smoother fuller rail turns, wider stance for the gouging off the tail turns. I also tend to stand further up compared to a modern short board. I’m riding an 8’6" single here and I’m quite a bit up from the tail. Wave is probably just head high.