: Today I've seen an unusual boat: a pinnace's tender. They're usually made of
: steel and hang from a cat-head or crane over the steerage. This one's made
: of ply and the joints were filletted with black tar. The plywood panels
: looked a bit blackened by tar, too.
: Worse, the rudder wasn't deeper than the keelson which was very deep indeed.
: I wonder if that dinghy was purely decorative or could those matt ply panels
: stand sun exposure with no epoxy or varnish?
: Fishing dinghies were painted but the chine joints were filled with tar. So
: were sewn boats.
: Is that a waterproofing alternative ? Did one of you ever use it?

Tar, and pitch, as waterproofing compounds, are centuries old. Sailors used to be called "tars" because they used this material for coating their ropes and lines, as well as painting the hulls, and considering the medium, they probably got a lot on themselves, too. American Indians used thickened sap from spruce and pine trees, (crude tar) to seal the seams on their birchbark canoes, and before that, there is reason to suspect they used these compounds to seal cracks in dugouts.

In his book on canvas covered boats, George Putz mentions the corracle, a craft that is frequently associated with Ireland, but is also found in ther areas. The canvas skin on these types of boats has historically be waterproofed with tar. He also has a picture oa corracle.

With plank on chine construction, a sealing compound so some kind is used in the joints. The planks meet at the chines, and are held to them by screws or nails. Gaps between planks are filled with oakum or cotton fiber, which is packed in, and covered with tar or paint, or both. The tar not only sticks to the wood through expansion, contraction and immersion, but tends to be somewhat "self healing" as it stays as a very thick liquid, until it gets warm.

Tar makes a mess. Dealing with tar is like dealing with an area of wet paint that never dries. Eventually it thickens and gets a skin over it, but contact with that stuff is almost always messy. With all the modern "miracle' sealants and caulks -- and even many old-fashioned linseed oil-based putties and caulks -- this is not the best sealant for boat seams. I suspect that any boat that has a lot of tar sealing the seams was built or repaired on a very tight budget, or in an area where better materials were not available.

PGJ