LMPROVEMENTS IN THE ARRANGEMENTS FOR AND METHOD OR MANNER OF OBTAINING THE PRE- SERVATION AND PREVENTION FROM FOULING OF SUBmerged or FLOATING IRON OR STEEL STRUCTURES, AND THE BOTTOMS OF IRON OR STEEL SHIPS AND STEAM VESSELS."
Year: 1879

page_text: LETTERS PATENT to Charles Frederic Henwood, of 28, Budge Row, in the
City of London, Naval Architect, for the Invention of "LMPROVEMENTS IN
THE ARRANGEMENTS FOR AND METHOD OR MANNER OF OBTAINING THE PRE-
SERVATION AND PREVENTION FROM FOULING OF SUBmerged or FLOATING IRON
OR STEEL STRUCTURES, AND THE BOTTOMS OF IRON OR STEEL SHIPS AND
STEAM VESSELS."
PROVISIONAL SPECIFICATION left by the said Charles Frederic Henwood
at the Office of the Commissioners of Patents on the 26th April 1879.
CHARLES FREDERIC HENWOOD, of 28, Budge Row, in the City of London, Naval
Architect. "IMPROVEMENTS IN THE ARRANGEMENTS FOR AND METHOD OR MANNER
OF OBTAINING THE PRESERVATION AND PREVENTION FROM FOULING OF SUBMERGED
OR FLOATING IRON OR STEEL STRUCTURES, AND THE BOTTOMS OF IRON OR STEEL
SHIPS AND STEAM VESSELS."
This Invention has for its object tho attainment of a ready and certain means
for obtaining the preservation of submerged and floating iron or steel structures,
and the bottoms of iron or steel ships and steam vessels, and preventing the fouling
of the same, and consists in an improved method or manner of applying sheet
metallic zinc, and in proportioning and arranging the extent and amount of the
same to be applied to the vessel or structure, and exposed to the action of the sea
water in order to obtain the above results.
The protection from fouling and corrosion afforded by zinc sheathing to an iron
or steel vessel or structure, floating or submerged in sea water, thus obtained
depends upon the galvanic action which takes place when the two metals are sub-
jected or exposed to the action of sea water, the zinc being the positive metal or
that on which the galvanic action takes most effect is gradually dissolved, whilst
the iron or steel being the negative metal, or that on which the galvanic action
takes least effect under the circumstances, remains intact, and is preserved at the
expense of the zinc which prevents the fouling and corrosive action on the iron or
steel,

page_text: It is not necessary that the entire surface of the iron should be covered with the
zinc sheathing, as within certain limits the unsheathed iron is protected and kept
free from fouling, nor does actual metallic contact partially or throughout appear
to be absolutely necessary, as the sea water itself becomes a medium of connection
sufficient to produce the action, whereby both the iron and the zinc are kept free
from the submarine organic growths which so materially affect the speed of an
iron ship where their presence exists. Various plans have been proposed, and
Letters Patent granted for modes supposed capable of attaining the object sought,
viz., the preservation and keeping clean of the bottoms of iron vessels and pre-
serving floating and submerged iron structures, none of which however appear to
have been effectual or successful, either by reason of structural difficulties or from
the prevention or diminution of the necessary galvanic action caused by the
greater or less insulation, resulting from the method of attachment of the zinc
sheathing to the iron.
By my Invention I obviate the difficulties hitherto experienced in carrying out
the objects proposed, and obtain the ends sought in a simple and practical manner
without needing, adopting, or applying any mode or arrangement that would
weaken or injure the structure, nor is it necessary to make any alteration in
existing iron or steel ships.
In carrying out my Invention on an iron or steel ship or steam vessel I apply
sheet metallic zinc to the part or parts exposed to or in contact with the sea water,
and cause the sheet metallic zinc to adhore to the iron or steel, which should be
clean and free from paint or grease by means of marine or waterproof glue, or such
other adhesivo material or materials or combination of the same as will resist the
action of sea water, or I may use in combination with the marine or waterproof
glue or other adhesive material or materials or combination of the same, thin sheets
or portions of india rubber, either pure or vulcanized, employing the marino or
waterproof glue or other adhesive material or materials or combination of the same,
both for attaching the india rubber to the iron, and also for attaching the zinc
sheathing to the india rubber, or the india rubber to the zinc sheathing by heat
and pressure combined, or by heat only, using the waterproof glue or other adhesive
material or materials or combination of the same only for attaching the so pre-
pared zinc sheathing to the vessel.
In attaching the zinc sheathing to the iron or steel plates or structure I apply
the waterproof glue, india rubber, or adhesive material or materials, or combination
of the same in sections, spots, patches, strips, or bands of suitable size and width,
disposed either vertically, diagonally, or horizontally in relation to the vessel or
structure, and in proportions varying from about one fourth to one half, leaving
the remaining portions free from all adhesive or protective material and accessible
to the sea water in order to obtain the required galvanic action; or I apply the
sheet metallic zinc to the inner or sunken strake only of the iron or steel plating
forming the shell or submerged portion of the vessel, in which case I cover the
entire or greater portion of the zinc with the waterproof glue, india rubber, or
adhesive material or materials, or combination of the same, obtaining the requisite
galvanic action from the outer and exposed surfaces of the zinc and iron or steel,
and where there may be too great a width of iron or steel plating exposed I
introduce an intermediate strake of zinc sheathing on the outer strake of plating of
the vessel; and in constructing a new vessel, by preference the outer strake of
plating of the ship should be less in width than the inner or sunken strako.
By applying sheet metallic zinc in this manner no special or different mode of
constructing ships is needed, and by carefully making the ends of the zinc sheets
square and even I am able to join the butts of the sheets so as to produce a flush
and even surface, and by fitting the sheets carefully to the width of the sunken or
inuer strakes they can be firmly attached to the hull and thus enable the sheathing
to be done in a workmanlike manner.
In some cases the butts or ends of the sheets of the metallic zinc where they join
may be formed with alternate projections and recesses, so as to fit into each other

page_text: when in their position on the ship or structure if desired or preferred, though the
butts may be lapped and rivetted together if desired, and at the stem and stern
keel and orifices I sometimes attach a stout strip of zinc by means of rivets, or
rivets and marine glue, or other suitable adhesive material or materials. The rate
at which the zinc must dissolve to keep the bottom free from fouling and obtain
the preservation of the iron or steel varies from one ounce per square foot of zinc
surface to three ounces per square foot per annum and upwards, according to
circumstances, and these also will govern to a certain extent the thickness of the
sheet zinc to be employed, the most suitable for general use being the gauges No. 15
of the zinc gauge (equal to 24 ounces per square foot) up to No. 19 or 32 ounces
per square foot, though of course where desired thicker sheets may be employed,
and these sheets may be made to last from three to seven years by paying due
regard to the amount of surface acted on.
Pure zinc will be found to wear more evenly than the cheaper and less pure
qualities, and for this purpose the sheet zinc of the Vieille Montagne Zinc Company
will be found to give the most satisfactory results, though it is obvious that other
sheet zinc may be used.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Charles Frederic Henwood in the Great Seal Patent Office on
the 25th October 1879.
CHARLES FREDERIC HENWOOD, of 28, Budge Row, in the City of London, Naval
Architect. "IMPROVEMENTS IN THE ARRANGEMENTS FOR AND METHOD OR MANNER
OF OBTAINING THE PRESERVATION AND PREVENTION FROM FOULING OF SUBMERGED
OR FLOATING IRON OR STEEL STRUCTURES, AND THE BOTTOMS OF IRON OR STEEL
SHIPS AND STEAM VESSELS."
This Invention has for its object the attainment of a ready and certain means for
obtaining the preservation of submerged and floating iron or steel structures and
the bottoms of iron or steel ships and steam vessels, and preventing the fouling of
the same, and consists in an improved method or manner of applying sheet metallic
zinc, and in proportioning and arranging the extent and amount of the same to be
applied to the vessel or structure and exposed to the action of the sea water in
order to obtain the above results.
The protection from fouling and corrosion afforded by zinc sheathing to an iron
or steel vessel or structure, floating or submerged in sea water, thus obtained
depends upon the galvanic action which takes place when the two metals are sub-
jected or exposed to the action of sea water, the zinc being the positive metal or
that on which the galvanic action takes most effect is gradually dissolved, whilst
the iron or steel, being the negative metal, or that on which the galvanic action
takes least effect under the circumstances, remains intact, and is preserved at the
expense of the zinc, which prevents the fouling and corrosive action on the iron or
steel.

page_text: It is not necessary that the entire surface of the iron or steel should be covered
with the zinc sheathing, as within certain limits the unsheathed iron or steel is
protected and kept free from fouling, nor does actual metallic contact partially or
throughout appear to be absolutely necessary, as the sea water itself becomes a
medium of connexion sufficient to produce the action whereby both the iron or
steel and the zinc are kept free from the submarine organic growths which so
materially affect the speed of an iron ship.
Various plans have been proposed and Letters Patent granted for modes supposed
capable of attaining the object sought, viz., the preservation and keeping clean of
the bottoms of iron vessels, and preserving floating and submerged iron structures,
none of which however appear to have been effectual or successful, either by reason
of structural difficulties, or from the prevention and diminution of the necessary
galvanic action caused by the greater or less insulation resulting from the method
of attachment of the zinc sheathing to the iron.
By my Invention I obviate the difficulties hitherto experienced in carrying out
the objects proposed, and obtain the ends sought in a simple and practical manner
without needing, adopting, or applying any mode or arrangemont that would
weaken or injure the structure, nor is it necessary to make any alteration in
existing iron or steel ships, but in the case of building new ships or steam vessels
an improved arrangement of the skin plating with longitudinal butt straps on the
outside, and butt straps at the butts of the longitudinals inside between the frames
is by preference adopted.
In carrying out my Invention on an iron or stoel ship or steam vessel I apply
the sheet metallic zinc to the part or parts exposed to or in contact with the sea
water, and cause the sheet metallic zinc to adhere to the iron or steel, which should
be clean and free from paint or grease, by means of marine or waterproof glue or
such other adhesive material or materials, or combination of the same, as will resist
the action of sea water; or I may use in combination with the marine or water-
proof glue or other adhesive material or materials, or combination of the same,
thin sheets or portions of india rubber either pure or vulcanized, employing the
marino or waterproof glue, or other adhesive material or materials, or combination
of the same, both for attaching the india rubber to the iron or steel, und also for
attaching the zinc sheathing to the india rubber, or the india rubber to the zinc
sheathing by heat and pressure combined, or by heat only, using the waterproof
glue or other adhesive material or materials, or combination of the same, for attaching
the zinc sheathing to the vessel.
In attaching the zinc sheathing to the iron or steel plates or structure I apply
the waterproof glue, india-rubber, or adhesive material or materials, or combination
of the same, over a portion only of the surface in sections, spots, patches, strips, or
bands of suitable size and width, disposed either vertically, diagonally, or hori-
zontally in relation to the vessel or structure, and in proportions varying from
about one fourth to one half of the zinc or submerged surface, leaving the remaining
portions free from all adhesive or protective material, and accessible to the sea
water, in order to obtain the desired galvanic action. In such caso the entire
surface of the bottom may be sheathed with zinc sheathing, and by preference I
then use india rubber or such combination as is herein beforo described, or water-
proof glue, as will retain its position, and not dissolve or soften and run over and
upon the parts desired to be kept free, for the purpose of permitting galvanic action,
the seams and butts being secured by lap joints or butt plates, and rivetted together.
When marine glue is used the iron or steel should be warmed or heated with a
portable fire or " devil" to or about the melting point of the marine glue, and after
the zinc sheathing is fixed in its place it should be similarly warmed or heated, and
pressed firmly or uniformly to the iron. When india rubber is used the iron, as
well as the zinc, being free from paint or grease, should be washed or coated with
naptha, as also the intermediate sheet of india rubber, and when placed in position
firmly pressed so as to exclude the air.

page_text: I make the "shift of butts" of the zinc sheathing to correspond with the "shift
of butts" of the iron or steel plating of the bottom, and at the junction of the iron.
or steel plates at the butts I drill one or more holes to the depth of the iron plates,
and plug the same with ebonite or compressed teak or other suitable material, and
pass a nail, rivet, or screw of an alloy less oxidizable than zinc, such for instance as
that composed of four atoms by weight of zinc to one atom by weight of tin through
the butt of the zinc sheathing into the compressed teak or other material, which
will materially assist in the retention and prevention of shifting or drifting of the
zinc sheathing. I may also apply the sheet metallic zinc to the inner or sunken
strake only of the iron or steel plating forming the shell or submerged portion of
the vessel, in which case I cover the entire or greater portion of the zinc with the
waterproof glue, india rubber, or adhesive material or materials, or combination of
the same, obtaining the requisite galvanic action from the outer and exposed surfaces
of the zinc and iron or steel, and where there may be too great a width of iron or
steel plating exposed I introduce an intermediate strake of zinc sheathing on the outer
struke of plating of the vessel, and in constructing a new vessel by preference the
outer strake of plating of the ship should be less in width than the inner or sunken
surface, and the longitudinal edges of such outer strake so formed by being bevelled
or grooved as to assist in the retention of the sheet zinc sheathing in its proper
place. With such object in view I place the whole of the skin plates of the hull
directly on the ribs or frames of the ship or vessel, butt to butt longitudinally, as
well as vertically, obviating thereby the necessity of the usual liners or washers
between the plates and frames on the plan patented by Lamb and Ronalds, No. 2798,
of 1856, with an additional butt strap at each butt of such butt strap. I then work
longitudinal butt straps of the required breadth with rounded or bevelled and
grooved or rabetted edges, with an additional width allowed for bevelling or grooving,
or such butt straps being rolled with such bevel or groove, or either or both, in
course of manufacture, or cut or otherwise formed afterwards. The vertical butt
straps I place inside the skin, as at present, but the plating being flush the necessity
and consequent expense of "joggling" the vertical butt straps of the skin plating
is also obviated. If greater galvanic action is desired than is obtained by this
arrangement with the longitudinal iron butt straps only exposed, the marine glue,
india-rubber, or such combination as has been bereinbefore mentioned may be
applied only to parts and at and about the centre line of each strake of zinc
sheathing; the butts of the zinc sheathing corresponding also with the butts of the
iron or steel plates may be further secured, as hereinbefore described, with a metal
nail, rivet, or screw, or I may sheathe such longitudinal butt strap also with zinc
sheathing, securing the edges and butts as shewn in the Drawings, and with or
without marine glue.
By applying sheet metallic zine in this manner no special or different mode of
constructing ships is needed, except and by preference as to the arrangement of
outside plating, as hereinbefore described, and by carefully making the ends of the
zinc sheets square and even I am able to join the butts of the sheets so as to pro-
duce a flush and even surface, and by fitting the sheets carefully to the width of
the sunken or inner strakes they can be firmly attached to the hull, and thus enable
the sheathing to be done in a workmanlike manner.
In some cases the butts or ends of the sheet of the metallic zinc sheathing, where
they join, may be formed with alternate projections and recesses so as to fit into
each other when in their position on the ship or structure, if desired or preferred,
though the butts may be lapped and rivetted together if desired, and at the stem
and stern keel and orifices, I sometimes attach a stout strip of zinc similar in form
to that shewn in Patent No. 2413, of 1867, granted to one MoIntyre, by means of
rivets, or rivets and marine glue, or other suitable and adhesive material or materials
for the purpose of protecting the ends of the sheathing.
The rate at which the zinc should dissolve, to keep the bottom free from fouling and
obtain the preservation of the iron or steel, varies from one ounce per square foot of

page_text: zinc to three ounces per square foot per annum and upwards according to circum-
stances, and these will also govern to a certain extent the thickness of the sheet
zinc to be employed, the most suitable for general use being the gauges No. 15 of
the zinc gauge (equal to 24 ounces per square foot) up to No. 19 or 32 ounces per
square foot, though, of course, where desired, thicker sheets may be employed, and
these sheets may be made to last from three to seven years by paying due regard
to the amount of surface to be acted upon.
Pure zinc will be found to wear more evenly than the cheaper and less pure
qualities, and for this purpose the sheet zinc of the Vieille Montagne Zinc Company
will be found to give the most satisfactory results, though it is obvious that other
sheet zinc may be used.
The accompanying Sheet of Diagrams will shew more clearly some of the ways
in which the zinc sheathing may be applied to iron and steel hulls as herein before
described, and some of the ways in which the butts or ends of the zinc sheets may
be secured.
Figure 1 is a section across a longitudinal butt strap and plates of the hull of a
ship shewing the grooves or rabbets in the strap into which the edges of the zinc
sheets enter, and how the external edges of the strap may be rounded, bevelled, or
otherwise. These grooves or rabbets inay be undercut or dovetailed as shewn, or
parallel, if desired. A, A, the butt strap; B, B, the iron or steel plating; C, C, the
grooves or rabbets in the butt strap; D, D, the zinc sheathing; E, E, the rivets
through butt strap; and F, F, the attaching portions of the marine glue or cement.
After the zinc sheathing is fitted into the grooves or rabbets and in the place it
is to occupy, and attached with the marine glue or other suitable waterproof
adhesive material, as herein before described, the grooves C, C, are to be filled in with
an alloy less electro positive than zinc, and, by preference, with an alloy of four
atoms by weight of zinc and one atom by weight of tin throughout their entire
length, or in sections or parts only, and compressed or caulked tightly, and the
edges of the sheet zinc may be left plain or turned over at right angles, as shewn
in the groove on the left. The grooves may vary in breadth and depth, and also in
form, according to the thickness of the plates and sheets, but a depth of a quarter
to half an inch will generally be found sufficient. Figure 2 shews the sheathing
over the longitudinal butt strap with the longitudinal lap or junction at G rivetted
as hereinbefore described. Similar parts are denoted by similar letters to Figure 1.
Figures 3 and 4 shew in elevation and section a butt joint of the zinc sheathing,
in which butt straps K with studs or rivets H attached thereto are employed, cor-
responding holes being punched in the ends of the sheathing, which, when fitted in
place, allow the studs or rivets to pass through, and these are then hammered down
as in the ordinary method of cold rivetting, and thus firmly connect the ends of
the zinc sheets; J, J, are screws passing through the butts of the zinc sheathing
into the butts of the iron or steel plating.
Figures 5 and 6 shew in elevation and section a lap joint for connecting the
ends of the zinc sheets similarly riveted, the rivets H being first placed in the
under sheet with the heads of the rivets towards the iron or steel plates.
Figure 7 shews a section of the thick strip of zine or other metal L for attaching
and securing the ends of the sheathing D at the stern stern posts, or as may be
desired.
Having now described the nature of the said Invention, and the manner in which
the same is to or may be performed or carried into practical use, I desire to state
that I do not limit or confine mpself to the precise details, as hereinbefore described
and illustrated in the accompanying Sheet of Diagrams, as the same may be
modified without departing from the nature of the said Invention, nor do I claim
as of my Invention the application of sheet zinc to iron or steel structures for the
prevention of the corrosion or fouling of the same, as this is not new, nor do I claim
as of my Invention the employment of an adhesive glue for attaching the sheet
zinc to the iron or steel, as this is not novel, nor do I claim the use of longitudinal

page_text: butt straps on the external surface of iron or steel ships, as these have been used
before, but what I claim as of my Invention, and desire to have protected by Letters
Patent is,―
First. The method hereinbefore described of attaching sheet metallic zinc or
other electro positive metal or alloy as a sheathing to the bottoms of iron or steel
ships or vessels by means of marine glue or other adhesive waterproof compound
applied to parts only of the surface, leaving other parts bare and free for the
purpose of ensuring and apportioning and regulating the extent of surface of the
iron or steel and the zinc exposed to the salt water, for the desired galvanic
action.
Second. The method of forming and arranging the longitudinal butt straps
applied to the outer surface of the plating of an iron or steel ship or vessel, with
grooves or rabbets in the edges, for the purpose and object of securing the edges of
the zinc or other electro positive metal or alloy sheathing, as shewn in Figures 1 and 2,
the sheathing being also attached by marine glue or other waterproof compound in
parts only, or otherwise over the entire surface of alternate strakes of sheathing,
the intervening narrow strakes being left bare and free from paint, and having no
marine glue or other waterproof compound, and attached only at the edges and
butts as herein before described.
Third. Leaving the outer strake of iron or steel plating bare and free from either
paint, marine glue, or other waterproof compound or zinc, or other electro positive
metal or alloy, and attaching to the sunk strakes the zinc sheathing by marine glue
over their entire surfaces, and in the case of new vessels securing the edges in
grooves or rabbets obtaining the desired galvanic action from the exterior and
exposed surfaces of the zinc and iron or steel.
In witness whereof, I, the said Charles Frederic Henwood, have hereunto
set my hand and seal, this Twenty fifth day of October, in the year of our
Lord One thousand eight hundred and seventy nine.