Eskimo in medium to big and you get pushed back way too far... It turns into a real battle just to get out back.
As usual it's different to duckdiving a shortboard. But practice is the key... It's quite effective once you get it sorted out.
Slice n duck is mostly technique, not muscle. Although bodyweight obviously helps a bit.
My 9'6" does it easy enough and I am 6'0" and 83kg.
From the same book (page 58):
What Really Big Aussies Do
Bill Stewart has told be this story twice so it must be true:
"Frank Latta and I were surfing some good size waves in Australia, maybe 10 feet, and we got caught inside. Along came this huge waal of white water and it looked like a problem. But Frank Stood up on his board, sank the tail first, then the entire board, and then completely disappeared underwater(!) The soup passed by him without a scratch.
"I saw him do that all day. Sinking the board like that just wasn't a big issue for him. I imagine, though, that it does take a high degree of skill to execute, and, like anything else, alotta practice to pull off."
(Sorry, no pix of this particular feat, although I wish we did. Maybe in the reprint.)
I particularly echo the author's last sentence.
If you have further questions or comments about (or against) the technique you might wish to ask Doug Werner (the author), Bill Stewart or Henry Ford (major sources). They are all highly skilled at the technique and strongly recommend it. You will find their email addresses easily enough of you have good search skills.
-doug