milky water

It's probably just oxidation. The gelcoat on our boats is very thick so you can usually restore to like new shine by removing the oxidation and then restore the shine by either sanding/polishing or using chemicals.

I never recommend painting beachcats unless it is to cover up damaged areas cosmetically or if you just hate the color of your boat.

+1 for gel oxidation, though paint can oxidize as well. If your hulls are white and not-yet-painted, there's a host of products and techniques to restore them. I've been a big fan of Collinite cleaner + wax for years.

http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?productId=24231&catalogId=10001&langId=-1&storeId=11151&storeNum=10104&subdeptNum=10379&classNum=10380

http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?productId=24224&catalogId=10001&langId=-1&storeId=11151&storeNum=10104&subdeptNum=10384&classNum=10386

This stuff's pretty amazing for hulls that are absolutely trashed: http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?productId=21614&catalogId=10001&langId=-1&storeId=11151&storeNum=10104&subdeptNum=10384&classNum=10385

Soap isn't going to cut heavy oxidation.

I've used this stuff to remove really heavy oxidation, works great.
http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?productId=109298&catalogId=10001

One thing to remember, after you remove your oxidation by whatever method, you need to seal the surface with either wax or one of the newer sealants, something like this would be good.
http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?productId=109254&catalogId=10001

It's not soap man, it applies like a cleaner wax and does wonders to remove heavy oxidation (wax on, wax off Daniel-san). Used it on a 1972 Albin Vega which was near oxidized to the glass in several spots. Brought it back from the dead. Then applied Collinite's wax and didn't have to touch it for a year.

If you have access to a power buffer, great, if not, you'll be upper body toned when you finish. If your hulls are dull, the milky stuff is just oxidized gel coat. The hulls are probably still shiny under the tramp. Mine are fairly dull and if I take a scotch brite pad, scrub a bit, then rinse I see a cloud of white.
I had plans to brighten the entire hulls, but decided to sail it hard for a year, then worry about cosmetics. I did one small area, as a test to see if the work would be worth it, & it definitely will shine up. I would do that before paint.

Headhunter wrote: It's not soap man, it applies like a cleaner wax and does wonders to remove heavy oxidation (wax on, wax off Daniel-san). Used it on a 1972 Albin Vega which was near oxidized to the glass in several spots. Brought it back from the dead. Then applied Collinite's wax and didn't have to touch it for a year.

My bad I was just going by where West Marine had it categorized.
West Marine > Maintenance > Cleaners & Protectants > Boat Soap

I'm a fan of chemicals instead of elbow grease, so whatever works. I used to recommend Barkeepers Friend and it does work and is cheap, but it's kind of harsh and leaves the fiberglass clean and white but very porous requiring more work to get a shine.

I use Starbrite Rust Stain remover...works great, very little elbow grease and polishes up very nice.

No worries D! I use sno bowl (toilet bowl cleaner) which, like barkeepers friend, also has oxalic acid.