Improvements in Means for Reducing the Skin-friction of Vessels.
Year: 1897

page_text: Date of Application, 4th Dec., 1897
Complete Specification Left, 2nd Sept., 1898-Accepted, 3rd Dec., 1898
PROVISIONAL
SPECIFICATION.
Improvements in Means for Reducing the Skin-friction of Vessels.
I, ROBERT SIMPSON BAXTER, Broughty Ferry, N.B., Merchant, do hereby declare
the nature of this invention to be as follows:
My said invention has for its object the lessening of surface or skin-friction
in sailing and steam vessels by the application of air, to part or whole of the
submerged portion of the hulls of vessels, in such manner that their velocity may
thereby be increased, under suitable circumstances.
I may effect this object by a suitably shaped and suitably placed air passage
or channel, or air passages and channels, arranged in, along, down, through, or
around parts of the hull, in such a manner that the movement of the water past
certain openings in the air passages aforesaid, (acting in the way of an aspirator)
will cause a supply of air to pass through those openings, into the water. The
air thus supplied being carried along outside the hull in such a manner as to effect
a lessening of the surface-friction or skin resistance.
·תו נד
of Traumhan 1807
COMPLETE SPECIFICATION.
Improvements in Means for Reducing the Skin-friction of Vessels.
I, ROBERT SIMPSON BAXTER, King Street, Broughty Ferry, County of Forfar,
Scotland, Merchant, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement:—
My said invention has for its object the lessening of surface or skin-friction
in steam and sailing vessels by the application of air to part or to the whole of
the submerged portion of the hulls of vessels in such a manner that their velocity
may thereby be increased under suitable circumstances.
I effect this object by a suitably shaped and suitably placed air passage or
channel or air passages or channels arranged in, down, through or around parts of
the hull in such a manner that the movement of the water past certain openings
in the air passages or channels aforesaid, acting in the way of an aspirator, causes
The air thus
a supply of air to pass through those openings into the water.
supplied is carried along outside the hull in such a manner as to effect a lessening
of the surface friction or skin resistance and generally, for whatever physical
reason, to increase the velocity under the application of a given power. For any
given vessel or boat the increase of velocity is greater the greater the normal
velocity of the said vessel or boat-that is its velocity without the use of inven-
tion-under the steam pressure actually employed. This is due to the fact that
the aspirating effect of the movement of the water past the openings referred t>,
my

page_text: which causes the level of the water in the passage or channel or passages or
channels aforesaid to stand continuously lower in the said passage or channel or
passages or channels than the level of the surrounding water, is greater the
greater the velocity of the vessel; and at higher speeds larger areas of the side
of the hull are covered by air carried along outside the hull from the aspirator,
or from each aspirator if there be more than one. In vessels of great draught the
areas covered by the air aforesaid at moderate speeds are proportionately smaller
than in vessels of light draught; so that for equal normal velocities the utility
of my invention tends to be smaller with vessels of great draught than with vessels
of light draught until the limit of speed is reached at which the water in the said
air passages or channels stand at the level of or below the keel of the said vessels
of greater draught. The most advantageous application of my invention is,
therefore, to deep vessels at high speeds or to vessels of light draught at moderate
and high speeds; but there is some utility in all cases where the speed exceeds
five (5) knots per hour. Further, the aspirating effect of the movement of the
water past the openings referred to is also greater the more directly these open-
ings, by which the air may escape into the water, look backwards in relation to
the forward travel of the vessel or boat; and it falls off in amount the more
laterally these openings are directed until when they are directed sufficiently
forward the aspirating effect is replaced by a pressure of water into the passage or
channel of the aspirator. In practical application of my invention for the pur-
poses thereof the openings by which the air may escape into the water should be
directed as nearly backwards as may be. The quantity of air which is kept stream-
ing past the sides of the hull is considerable in amount and is of greater volume
the greater the speed of the vessel and the flow of this air is continuous and
automatic.
Having described the nature of my invention I proceed to describe the manner
in which the same is to be performed.
According to one form of my invention I construct a false stem and keel or part
of keel, of approximately V-shaped cross section, as may be readily done out of
sheet metal, and I connect this to the stem and keel of the vessel so that water
cannot flow into the passage or channel between the vessel and this addition
thereto, except through the lateral apertures hereinafter mentioned. The false
stem ascends above the external water level and with the vessel to which it is
connected it forms a tube, of approximately V-shaped section, open to the air
at the top. At each side of the false stem and keel I provide apertures preferably
vertical opening into the passage or channel in the interior of the tube aforesaid,
and to increase the effect I in practice provide each of these apertures with a
shallow shield or hood so shaped that any air travelling down the stem and issuing
through the said apertures may be deflected backwards so as to emerge through
vertical chinks and impinge upon the sides of the hull or pass backwards under
the same as the case may be. The said shields or hoods should as near as may be
follow the lines of the vessel. Or otherwise I may cause the said apertures to look
backwards towards the side or under the hull of the vessel or boat by cutting
slits preferably vertical in the metal of my invention and shaping on the sides of
these slits and the metal surrounding the same by hammering, by pressure or
otherwise so that these slits widen out into apertures directed backwards such that
air issuing therefrom may impinge or pass backwards as aforesaid.
According to another form of the same I construct a false stem and keel or part
of keel of approximately V-shaped cross section as before and in the same manner
as before but without any of the lateral apertures and hoods or shields aforesaid
upon the stem or ascending portion of my invention; and I connect the same
watertight to the keel of the vessel in the same manner as before and connect the
lower few inches of the false stem watertight with the stem, but con-
nect the remainder of the false stem with the stem of the vessel and overlapping
the same with the aid of distance pieces so as to leave open chinks between the
false stem and the stem of the vessel on both sides of the latter.

page_text: According another form, where the vessel is of deep draught, I dispense with
the false keel and rely upon a false stem only which may be constructed with
lateral apertures which may have hoods or shields or be shaped out as before; or
the false stem may be constructed simply with an approximately V-shaped section
and connected with the sides of the stem and overlapping the same with the aid
of distance pieces leaving chinks as before.
In another form of my invention the aspirator, instead of being made up by
connecting open metal with the stem or stem and keel or stem and part of keel
of the vessel and thereby forming a passage or channel as before described, is
built in so as itself to form the stem or stem and keel or stem and part of keel of
the vessel and the apertures by which the air escapes into the water may be made
and hooded or shielded or may be shaped out as hereinbefore described.
In long vessels or under moderate speeds the ascent of the air in the water
tends to leave certain areas of the submerged hull uncoated by air and in such cases
the aspirator at the stem may be supplemented by others situated further aft. In
one form each such aspirator may be built into the side of the vessel in the form of
a thin hollow space open to the air at the top and provided with external apertures
which may be made and hooded or shielded or shaped out as hereinbefore described.
In another, where the speed of the vessel is sufficiently high or her draught
sufficiently light to enable the water level within the aspirator to sink below the
level of the keel, I build into the ship an air pipe or air pipes with its or their
upper end or ends open to the air and situated on the deck or otherwise sufficiently
above water level. The lower end or ends of this air pipe or these air pipes I
connect with a passage or channel running along the keel and provided with
apertures which may be hooded or shielded or shaped out as herein before described.
which passage or channel may also be connected with the aspirator situated at
the stem. Or I may connect the lower end or ends of this air pipe or these air
pipes with passages or channels running along the sides of the vessel below water
level and provided with apertures as aforesaid; or I may connect the said lower
end or ends with passages or channels running down the sides of the vessel and
provided with apertures as aforesaid.
The dimensions of the false stem or false stem and keel or part of keel will
depend on those of the vessel to which they are to be fitted. The metal must be
of sufficient strength to act as a cutwater. In any case the air passages or channels
and chinks and apertures must be large enough not to wire-draw the stream of
air passing through them, the volume of which will within wide limits depend
upon the readiness with which the air can flow down the passages or channels and
out through the apertures and chinks. By the width of a chink I would under-
stand say from an eighth of an inch to two inches according to the size of the
boat or vessel. The precise shape of the cross section of the aspirator placed at
the stem and keel, which I have called an approximately V-shaped cross section,
would for the best result have to be determined in accordance with the rules of
naval architecture so as to harmonise with the lines of the vessel.
And that the foregoing description of my invention may be more readily under-
stood I hereunto append by way of illustration 2 sheets of drawings. The same
parts are marked throughout by the same letters.
In Fig. 1, Sheet 1, I show an elevation of an outside skin or aspirator B con-
stituting a false stem and keel or part of keel on which at intervals are attached
shallow shields or hoods A covering the apertures D Figs. 7 and 8 through which
the air flows.
In Fig. 2 I show Fig. 1 in plan at o y.
Fig. 3 is a section through a, Fig. 1.
Fi 4 is a section through b. Fig. 1.

page_text: Fig. 9 is a sectional plan through k 1, Fig. 1.
In Fig. 2 may be seen the deflection or angle of A over the slit D so that the
air issuing therefrom may impinge or pass backwards on B Fig. 1.
At C, Figs. 2, 3, 4, 5, 6, 7, & 9, may be seen the aperture between A & B
Figs. 2 & 7, by which the air escapes into the water.
In Fig. 10 is shown an elevation of part of a ship's side F showing 2 shallow
shields or hoods A covering the apertures D and connected with internal air
pipes with their upper ends open to the air and situated on the deck or otherwise
sufficiently above waterlevel.
Fig. 11 shows a section of Fig. 10.
Fig. 12 shows in section the method of conducting the air to the lower or after-
more opening D Fig. 10 covered by shield A and emitting the air to the water
at C.
I am aware that the use of air as a means of reducing friction between a vessel
and the water has been previously tried, the air being pumped by a force pump
through apertures in pipes laid along the stem or the stem and keel, and I make
no general claim for the use of air for this purpose; but having now particularly
described and ascertained the nature of my said invention and in what manner
the same is to be performed I declare that what I claim as my invention of
Improvements in means for reducing skin-friction of vessels" is:-
66
First: The construction and use down or along the stem or down the sides of
a vessel of any size of a passage or channel or passages or channels open above into
which through apertures or chinks in the walls thereof water from the surround-
ing water may enter so as to find its level within the same and may be drawn out
when the vessel is in forward motion so as to admit air from above in the place
partly or wholly of the said water and allow air to be continuously drawn through
the said apertures or chinks or some of them according to the greater or less
forward velocity of the said vessel and to escape alongside or under the hull and
to be carried along the surface thereof all substantially as and for the purposes
described.
Second: The construction and use, in combination with the subject matter of
Claim 1 hereof, of a continuation thereof by a passage or channel or passages or
channels running along the keel or along the side or sides of the said vessel to a
greater or less extent, and provided with apertures in the walls thereof all made
substantially as and for the purposes described.
Third: The construction and use in combination with and in continuation
with an air pipe or air pipes, open to the air at a point or points sufficiently above
the water-level upon or within a vessel or boat of any size of an air passage or
channel or air passages or channels running down the side or sides of the vessel,
along the side or sides of the vessel or along the keel of the vessel, and provided
with apertures in the walls thereof all made substantially as and for the purposes
described.
JNO. L. SCOTTLYON,
ROBERT SIMPSON BAXTER.
Engineer, 31, Reform Street, Dundee, Witness.
WM HAXTON.