Leaving yoru beach cat in the water for long periods is not good for two reasons.

1) Normal gelcoat and epoxy paint are not truly waterproof. Over time water will get into your hulls and wreak havoc on the fiberglass sandwich. You need to use a barrier coat that is formulated to block the water penetration. Many of these also have anti-fouling additives to help with algae growth. Clear, don't know of one. White, I think I have seen one before.

2) The waves bang the heck out of your rigging. Not only does the mast rotate from stop to stop, but since your shrouds are not tight the mast will wobble around and shock load your shrouds, forestay, and all connection points. Not good for the hardware. All kinds of damage can occur over time. To prevent this you have to tension your rig so it is no longer loose. I like to tension one shroud and use the jib sheet on the mast rotator (Like John said) to tighten down the rig.

I have never left my boat sitting in water for longer than a few hours while not sialing so I have no experience with the barrier coat.