Completely rinse it twice at a minimum. The first time will disolve the salt, then wait a couple minutes and rinse it off again.
It's best however, to give the boat a top-to-bottom bath in a good boat wash after every use.
And make sure you remove all water spots, stains, etc from all stainless hardware. In other words, don't let it air dry, wipe it all down.
And a product called 'salt-away' is great for flushing the engines.