I lived almost on the sea for most of my life and have never had a problem with the air beside the sea. Unless it is blowing a gale and there is a mist blown off the waves in the form of tiny water droplets then you don't have a problem. The most significant danger to any precision instrument close to the sea is sand, that can get into almost any crevice and cause untold damage.

If you are not sure about water droplets blowing off the sea, go for a 10 minute stroll in the area you want to photograph with your arms bared to the air. Then after the 10 minutes, lick the skin and if it tastes salty then you have salt in the air.

However a beast like a Hassie will stand an awful lot of exposure before it begins to affect it, just give it a good wipe down afterwards. make sure you have a filter over the lens, that will save the front element.