Those are some -seriously- rusty boats! I was going to say that a
warship wouldn't usually be as badly rusted as that, but then I saw the
destroyer in the last photo. What nationality and type is it? Is it a
ship in current service, or a scrapped/mothballed one?
Anyway here's what I do to represent rust weathering: For larger-scale
models (1/72, 1/150 etc.) I use a "wash" of burnt umber oil paint
heavily thinned with turpentine/white spirit. Apply it with a fine
brush to the point where you want the rust, and the wash will run into
crevices and/or down the hull of the model, giving very
realistic-looking rust streaks.
I used this technique on the 1/72 Flower-class corvette (HMS Bluebell)
I built earlier this year, I posted some photos of it on
Modelwarships.com a while ago but will also post them here if anyone is
interested.
On smaller scales such as 1/600 and 1/700, possibly even 1/350 and
1/400, the oil wash technique tends to look too heavy and "overscale",
careful drybrushing (or maybe weathering chalks as used on armour
models) is the best option in this case.