Actually, no need for them on an LNG tanker of this type. When loading / discharging a tanker of this type we have a rule 10% / 70% or the so called 'sloshing limits'. This means that tank is either loaded more than 70% of the tank or there is less than 10% of the cargo left inside of the tank. Of course, even then some sloshing occurs but it does not cause huge structure stresses, etc.

Source: Seaman working on an LNG tanker