caring for a mirror in a costal region

Once a year I have to spend a month teaching at a place near the coast and it's a good dark site. So I was using a 10" dob that I brought along with me.

The site is a mere 100 meters from the beach and I'm not that mobile while there since I don't have a car. So, for all practical purposes, I have to do my viewing (and day-time storage) there near the beach.

I've noticed that after a few days, even when keeping the mirror carefully covered during the day, that a film develops on the mirror. It must be salty. I say this because it reminds me of the layer of precipitate one finds in an evaporating dish after leaving a dilute solution to dry.

After about 2 weeks, the film on the mirror surface begins to obscure & scatter light, making it hopeless for star-gazing. I noticed that it takes quite a bit of rinsing in water to clean the mirror.

I'm not sure how to counter this problem. I must necessarily leave the mirror exposed in order to view at night.

Because of all this, I've been considering the possibility of switching from a reflector to a refractor for these viewing sessions.

Any thoughts from those who have encountered similar problems.

Clears,
Joe

I presume the scope has a shroud or solid tube already? That would certainly help.

I try to park the scope horizontally when not actually observing, and aimed away from the beach, so junk blowing off the ocean is less likely to settle on the mirror. Get some sort of water-proof cover and keep the scope covered as much as possible (though it will need to be uncovered to cool around sunset). A canopy or something similar will help keep the sun off the scope during the day, so it will need less time open to cool in the evening.

Could you fashion some sort of cover for the front of the mirror? It might allow you to cool the scope at sunset, while keeping the mirror protected a little longer. My Meade LightBridge had a mirror cover, and that seemed to help.

I've not had serious problems with mirrors collecting stuff -- not to the point of damaging the views. But my experience is limited to 1 week stays near the beach, so I am not sure whether I would have much worse problems at 2 or 4 weeks.

Would it be possible to fill a spray bottle with distilled water and spray off the mirror after observing sessions (i.e. spray with some force to dislodge stuff)? Followed by pouring more distilled water over the mirror to rinse -- hopefully the poured water will sheet-off leaving it nearly dry. I have seen fellow observers at the beach doing something similar, though I've not tried it myself. It will depend whether you can easily reach the mirror, and if your scope structure can tolerate being wet.

I suppose with the refractor you could get a protective clear filter to put over the front. Or perhaps carry the scope farther from the water when not observing. But otherwise the refractor lens will be similarly exposed to the stuff.