Are jet ski stabilizers necessary

Fuel stabilisers are necessary if you leave your jet ski in storage without draining the tank. The fuel must be cleaned and stabilised with a conditioner before being used, but sometimes needs to be completely drained. A qualified technician is trained to dispose of the drained fuel.

If you mean flotation stabilisers, these are only really required on older, sit down models, some of which are inherently unstable whilst at a standstill.