IMPROVEMENTS IN SHEATHING IRON OR STEEL SHIPS OR VESSELS WITH ZINC OR OTHER METAL OR MATERIAL NOT GALVANICALLY DESTRUCTIVE TO IRON IN SEA WATER
Year: 1868

page_text: PROVISIONAL SPECIFICATION left by Nathaniel Barnaby at the
Office of the Commissioners of Patents, with his Petition, on the
24th July 1868.
I, NATHANIEL BARNABY, Naval Architect, of Park Villas, High Road,
Lee, Kent, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN SHEATHING IRON OR STEEL SHIPS OR VESSELS WITH ZINC OR
OTHER METAL OR MATERIAL NOT GALVANICALLY DESTRUCTIVE TO IRON IN SEA
WATER," to be as follows:-
The improvements consist in forming a cavity in the points of the
rivets which fasten the bottom plates to the frames and to each other,
in which cavity a softer metal or material is placed or driven, which
softer metal is not capable of injury by the galvanic action of the bottom
plating or of the sheathing, or only so to a small extent, and is either
the bed to receive the fastening or is itself the fastening of the sheathing.
The improvement is applicable both to hot and to cold rivetting. For
hot rivetting the rivets are formed with a central axial hole extending
from the point inwards as far as desirable. These rivets are heated and

page_text: worked in the ordinary manner for the countersunk work of the bottom
plating. In beating the point into the countersink it will be found that
a part of the axial hole is filled up with the hot metal and a part in the
interior is left vacant. While the point of the rivet is still hot a punch
somewhat smaller than the original hole, say of an inch smaller, is
driven through the metal which covers the hole, and a cavity is thus
formed in each rivet larger on the inside than on the outside. In order
that the shearing value of the rivet may not be improperly reduced
thereby the central hole should either be stopped at one diameter of the
rivet from the shoulder so that there may be the full section of the rivets
at the joints of the plates to be connected (the plates being always less
in thickness than the rivet is in diameter), or the cavity being taken up
to or near the shoulder the rivet should be increased slightly in diameter,
or should have steel substituted for iron. The whole or any desired
proportion of the bottom rivets having been thus prepared, and the
bottom payed over or not with composition and covered or not with felt
or other substance, the sheathing may be brought on and fastened by
driving through the sheets and into the points of the rivets nails or pegs
of lead, lead alloyed with tin, nickel, or other soft metal not attacked
galvanically by the sheathing and but slightly by the plating. It has
been found that lead alloyed with one-fifth or one-sixth part of tin is
sufficiently strong and soft for this purpose with zinc sheathing. Such
nails or pegs spreading out on the inside of the cavity effectually secure
the sheathing.
In applying this Invention to cold rivetting the rivets are formed
similarly to those intended to be used hot, but it is desirable to give the
hole some appreciable degree of taper from the outside inwards, so as to
thin the lip round the hole and thus facilitate the beating of the point of
the steel or iron rivet into the countersink. It is expected that this
facility will lead to the more general adoption of cold rivetting in order
to avoid the unknown and sometimes dangerous strains put on hot rivets
(especially of steel) by cooling. But in this case the cavity in the point
of the rivet is filled in with the softer metal before it is used, and the
rivets may be provided in this form by the maker. With such rivets
the sheathing is fastened by nails of hard metal, say of steel, wrought
iron or cast iron, which are driven through the sheathing into the soft
points of the rivets. Such harder metal will not be affected galvanically

page_text: by the sheathing. In cases where the plating is stiff, and it is found
that the cold rivets will not draw the work home, only a portion of the
edge and butt rivets, as one row, for example, need be put in cold, but
the frame rivets may all be cold. It is desirable that such rivets should
be of mild steel, combining ductility superior to that of iron with
15 or 20 per cent. increase in shearing strength. In repairing or
replacing sheathing put on in this manner zinc sheets will be found to
strip with nearly the same facility as copper from a wooden bottom.
The soft metal may be extracted by a jet of gas or by a boring tool, and
the subsequent operations will be the same as sheathing originally. This
mode of sheathing is applicable to any form of plating, whether lap-
jointed or flush, although the latter is preferred. If lap-jointed, the
sheathing plates may be of the same size as the exposed surface of the
bottom plates, the overhanging edges being neglected. These edges
should then be protected with the ordinary preservative and antifouling
compositions in order to protect them from any injurious action of the
oxide of zinc or other sheathing metal, and to keep them free from weeds.
In this case some additional rivets may be required to receive the edge
fastening of the sheathing on the inner plates. It is found that the
waste of zinc when thus brought into connexion with iron in sea water,
there being a layer of felt between, is about as rapid as that of copper
on a wooden bottom. One difficulty will be anticipated by practical
men in this Invention, viz., that of placing the holes in the sheathing
so as to "hit" the holes in the rivets. To overcome this difficulty it is
proposed to "hit" two or three holes in the centre of each sheet, either
by "spiling" for them or by placing a steel pin in the rivet points
beforehand, which projecting from the bottom shall force its way through
the sheet. The sheet being suspended or fixed by these is then "dressed
home" in the usual way. The points of the rivets which are to receive
fastening should have been left full and a little pointed, so as to mark
themselves on the sheet as it is "dressed," or this operation may be
more easily performed where the sheathing is stiff on thin-covering felt
or other material, which felt should after having been punched be laid
upon the sheet as a template.
Another mode of avoiding this difficulty, by which also lap-jointed
plates may be entirely covered with sheathing, is by employing narrow
strips of the sheathing metal to receive the fastening at the edges and

page_text: butts of the plates and at the frames, to which strips. the main sheets
be afterwards attached in any convenient sizes by soldering. In
these strips the holes in the rivets may be easily "hit," and the process
may
of soldering has been found to be cheap and efficient as an adjunct to the
main fastening at the rivets, which forms the subject of the Invention.