More than likely it was coal tar epoxy. Basically an inexpensive alternative to bottom paint. I used it on my boat for both the interior and bottom of my steel hull. It sell for about $ 25.00/gallon and works beautifully. Several of the paint companies manufacture it. I used Ameron Coatings.
Tin based paints are illegal. The Core of Engineers uses CTE on underwater steel and concrete structures. Seals up bottom very well. Very popular on Metal boats. Only draw back is that it is not a very good anti-fouling material. Lasts 5 to 7 years with bi-annual scrape and abrasion touch ups. If used as a bottom sealer and anti-abrasion coating use the boat 1 season before applying antifouling. This material is good "stuff". I used it on my last 6 boats.
Edited: 01/09/2008 at 07:46:52 PM by OLD HOUSEBOATER