POR-15
POR-15 is a single component primer that, like
OSPHO, can be applied directly to bare steel. It is available in a few colors, but I have only used grey.
I always first prep with one of the various
phosphoric acid products, then I apply POR-15 or some other primer. Thus far I have used POR-15 in the bilges located immediately beneath the engine room entrance.
Once POR-15 is in contact with skin for more than a few moments, it will never wash off. After about 2 weeks your painted skin will sluff-off, revealing fresh unpainted skin. I have been able to remove all other paints by washing with acetone and by scrubbing with soap and a finger-nail brush; but not POR-15.
A number of comparisons with other rust prevention and corrosion products have been floating around the internet, but none I have located are done by an independent organization.