The Max amount / Safe amount of weight for surfing

My 02 Mobius will seat 10 people and or 1350lbs, now I heard of people putting 1500lbs + in their boats for surfing. And I’ve seen a few pictures of someone’s Outback on here looking like it’s damn near sinking in the back corner from have a ton of weight. And I know the newer boats can hold must more weight… but what is the most I can load up my 02 with and still be safe???

Thanks