hello, picked up a trailer from work that was under a seadoo inflatable. got the trailer for free so i can't complain. it just needs an axle. What size axle would be suitable for a 4 stroke ski?

ski is a yamaha xlt1200 hull with a yamaha 4 stroke in it. weight is around 800 lbs.

seing what others would go with. square or round axle. i have all welding equipment at work and a trailer supply store right across the street. trailer is galvanized already but needing an axle. will be dipped in salt water unfortunately.