Why dont ships rust in salt water?

Question

Why dont ships rust in salt water?

Answer 1

They do.

Zincs have to be changed.

Paint must constantly be applied.

And boats get hauled to repair and maintain.

Answer 2

they do.

but if i recall correctly, they attach copper strips to them, which sets up a minor electric current, significantly slowing the steel corrosion.

Answer 3

marine grade steel plate,or iron plate,

Answer 4

who said they don't? They most certainly do! maintenance is a constant on any ship that contains metal. There are thigs you can do to slow the rust process. Part of the problem is there is an interaction between the metal on the boat and the salt water which causes electrolysis. this means that a current is formed which causes pitting and ruse on metal. even aluminum. Adding a "zinc" ball to the propeller shaft helps. Zinc being a better conductor and a weaker metal, the electrolysis attacks it first, slowing the process on the rest of the boat. But, you have to replace the zinc ball at close intervals. Then, salt water itself is corrosive to steel/iron etc. So, that is why you see rust streaks down the sides of the ship. As I said, maintenance is ongoing, you must scrape,sand, primer and paint almost non stop to stay ahead of the rust.

Answer 5

They do.The bigger ships that are too large to be hoisted out of the water are "dry docked". Either Discovery channel or National Geographic channel had a program on this several years ago. The ship is brouht into port ,put into a 3 sided dock, which has a door that closes it off from the channel of water it came in. Much like the locks on a canal, similar to lets say the panama canal. At the bottom of the dry dock are v- shaper blocks,divers line up the ship to sit in these blocks , and the water is then pumped out until dry, exposing the hull of the ship. I'm sure there's quite a few seamen and sailors who could follow with much more detail.

Answer 6

Actually... they do.  You probably just haven't been close enough to one, long enough to notice.

Because moisture is the leading cause of rust, all boats with any metal or wires are common victims of rust. Water alone is bad enough, but when you add saltwater to the equation,  rust can be a big problem. Not only can water do damage, but the moisture in the air (especially sea air) can wreak additional havoc on a boat and its electrical components.

To combat rust we regularly wash as much of it as possible  with clean fresh water and a mild detergent after. In addition, we do routine inspections and use a lot of WD40 and Boeshield T-9 to try and keep the rust and corrosion under control. There products are extremely helpful in a combination of solvents, lubricants, and waxes designed for penetration, moisture displacement, lubrication, and protection. Boeshield T-9 dries to a thick waxy film that clings to metal. It can protect engines, electronics, deck hardware, wiring, and more. Furthermore it is non-conductive and will not cause short circuits. It is also safe on paint, plastics, vinyl, and epoxy.

Our hull is steel... but it gets a good coat of epoxy, and then a good number of coats of epoxy paint, and then a top coat above the water line and bottom paint below. So... thank you for your question... It is nice to know we are doing such a good job, that you would think it doesnt rust.

Answer 7

Ships do rust in salt water. That is why they are painted. Paint seals and protects as well as colors.

Regards,

Dan

Answer 8

They do, that is why they drydock them every once in a while to scrape the hull and repaint.

Answer 9

these days they can put all kinds of stuff on the ships to prevent rusting.

Answer 10

they do.

Answer 11

On smaller parts such as rudders and drive shafts, zinc's are attached as sacrificial lambs to the erosion process.  In addition to rust, salt water is a great conductor between dissimilar metals and can raise havoc.  Zinc is more attractive than steel, so it is attacked first.  As the zincs become smaller in size, you simply replace them.

As earlier posters noted for steel hulls on large ships it's the paint that is doing all the hard work of keeping rust at bay.  If you check out a fishing vessel towards the end of the season, you'll see plenty of rust that will be painted with a rust inhibitor and topcoat during the off season.