I have seen the hulls in movies flexing with paint popping off, skin separating from the frames, etc. Is that true or just Hollywood? How long does the paint last on the big boats?
May not be quite push-button, but I saw a leech-looking thing vacuum-attached to a cruise ship on Dirty-Jobs that used a water-blast procedure to remove the old paint from the large, even surfaces.
What about the electrolysis thing? Will the paint (properly bonded) keep the surface underneath from being attacked?
Mivey:
How long the paint lasts depends on the service the ship is in. A "harbor queen" that sits on her own coffee grounds might go five years, a containership that makes a habit of docking in Northern Europe, where 10 and 12 foot tides mean you'll be scraping the dock...a lot, or scooting in and out of Asian ports, (with Asian tugboat captains), is going to need a "shave and a haircut" more frequently. Modern two-part epoxy paints have been a godsend over the red lead and oil-based enamel days...
And yes, the flexing and skin separation is NOT Hollywood...it's what happens over the course of a few years worth of painting over, rather than removing, rust. A ship I once rode, the SS Green Island, (LASH Barge Carrier),caught a rogue wave in mid-Atlantic, and more than 60' of hull plating fell away and into the sea. Green Island took an immediate 15'-20' list, but the Chief Engineer, (I'd sailed for him when he was First), managed to counter-flood her to 5', and they were able to make Bermuda for repairs.
Charlie got awarded "Mariner of the Year" for that feat, while the Coast Guard covered the behind of the corrupt and lazy ABS inspector in Singapore who had "gundecked" his inspection regime by creating the novel and heretofore unheard-of phenomenom of "super rust"...that supposedly turned a perfectly hale and hearty mild steel plate into crap within a two-year span.
What you probably saw on "Dirty Jobs" was ultra-high pressure water blasting...pump the stream to about 40k psi, and all the bad paint goes away very quickly, while the good paint remains. It's frankly better than sandblasting, (since you're not inhaling as much Nasty Things).
Yes...properly bonded paint is a good insulator, the problem though, (and why I and the USCG get bent about using the hull as a conductor), is that where you have two dissimilar metals touching, say along the weld seams,(since there's always impurities and slag from the stick), you'll have electrolysis...immerse this in salt water, and you'll have accelerated electrolysis. Now pass a current through the whole shebang, and you might as well turn your rudder bearing or your shaft gland into a sacrificial anode...and we have anodes already installed on the hull to keep that from happening.
