I'm not sure where you saw "obs seat" but I'm sure someone just abbreviated the phrase "observer's seat" which simply means the seat across from the driver traditionally occupied by the observer of the skier (required by most states' laws). The ballast bags in these boats are mostly plug and play so you replace a smaller or "stock" bag with an aftermarket larger bag to increase the available weight. Good luck to you!
My Mom said I'm not allowed to get wet!
2008 LSV (sold)
2000 Outback LS (sold)
LLTR!!!!!!!!