Zawan-Dachi 座湾立ち (Description: ‘Wide-Seated Crossed Leg Stance’. Literally, in Nihongo: ‘Seated Bay Stance).
Zawan-dachi is essentially a wide Kosa-dachi which allows for maximum KOSHI NO KAITEN.
This tachikata is found in several Ryuha/Kaiha but is no longer commonly practiced in mainstream Shotokan (outside of the students of Asai Sensei, and offshoots from his influence within the old ‘pre-split’ JKA).
As alluded to above, it is primarily used for TENSHIN WAZA—rotational/spinning techniques; in particular, kaiten-uraken, kaiten-enpi, kaiten-shuto, haito, and various keriwaza. In IKS we also practice it with tsuki and with partner resistance. Rather than for practical application this challenges and develops core stability/balance and internal awareness of these aspects: especially when engaging in rapid movements. Consequently, this improves explosiveness in the standard Shotokan-ryu waza.
左足前座湾立ち (Hidari ashi mae zawan-dachi) with 左回転裏拳 (Hidari kaiten-uraken).
A major advantage of spinning in this stance (as opposed to zenkutsu-dachi, kiba-dachi, etcetera) is that it done immediately (on the spot by simply compressing). Compare this to movement nine of Heian Sandan etc...
In practice, these spinning techniques are made to frontal targets, which is very powerful but requires significant fine motor skills.
While this is certainly applicable, the main application of Zawan-dachi—in actual self-defense—is against attackers at one’s side or rear. This requires minimal fine motor skills (and capitalizes on the the more difficult frontal attacks practiced in the dojo).
右足前座湾立ち (Migi ashi mae zawan-dachi) with 右回転猿臂 (Migi kaiten-enpi).