cockpit drains almost corroded through

Whilst greasing the Blakes seacocks under the cockpit, I noticed that the cockpit drain fitting consisted of a brass piece (chromed surface, the drain you see in the cockpit), a cast iron 90 degree bend and a piece of copper tube over which the drain hose was attached.
The brass drain was fixed with a pewter looking nut, the cast iron bend had some superficial corrosion at the outside and the copper tube was welded or soldered to the cast iron bend.
I never trust a mix of metals connected to each other on salt water as electrolytic corrosion is a serious danger.
So I tried to remove the drain: The nut broke in many pieces. I then sawed through the drain and took the pieces home. At home I sawed the entire set in two (lengthwise).
There was a serious crevice between the copper tube and the cast iron bend, with a minimum remaining thickness of material of less than 3 mm (less than 1/8").
There was a lot of corrosion on the inside of the cast iron bend. I removed all corrosion at some places and found a pit with a remaining wall thickness of approx. 1.5mm (1/16") !
Our Contessa will have new cockpit drains when she goes back into the water this spring...

But I wonder: was the construction I found aboard Dolphyn common? If so, there could be more Contessas around with potential holes less than an inch above the waterline.
Please, check your cockpit drain fitting if you're not sure. You can't see the damage at the inside (where the salt water is doing its damage), but you can see its construction (a sticking magnet will tell you if the material is normal steel or cast iron and different metals should ideally not be fixed to each other).

HTH,

Hi Colin,

So drain construction was standard. I have informed the Dutch Contessa Association as well, I hope it helps prevent disasters.