CERTAIN IMPROVEMENTS IN SCREW PROPELLERS
Year: 1854

page_text: PROVISIONAL SPECIFICATION left by Richard Howson at the Office of
the Commissioners of Patents, with his Petition, on the 9th January.
1854.
I, RICHARD HOWSON, of Manchester, in the County of Lancaster, Engineer,
do hereby declare the nature of my said Invention of "CERTAIN IMPROVEMENTS
IN SCREW PROPELLERS " to be as follows, that is to say :-
It consists, firstly, in shaping the blade in such a manner that the part
nearest the boss, which is least effective in propelling, may pass with greater
ease through the water, and at the same time cause the stern slip," which would
otherwise take place at that part, to assume a direction more towards the
circumference, so as to accumulate a greater degree of resistance for the outer
and more effective part to act upon. The form which I give to the blade for
this
purpose is shewn in Fig. 1, of the accompanying sketch. Here it will be
seen that every cross section taken at right angles to the axis is compounded of
two curves running into each other, the first commencing at the circumference
of the boss and bending backwards from a to b, or thereabouts, while the
other continues from 6 to c, and bending the contrary way. Thus the part
from a to b. passes more easily through the water than if it were radial, and

page_text: by its shape assists the centrifugal force in creating a current towards the
outer part, which is moving at a higher velocity and acting with a more
efficient angle. As this current or slip," when the vessel is in motion, will thus
always take place in a diagonal line, in order that it may not pass away without
being caught by the exterior and propelling part of the blade, I give the lead
to the part nearer the centre or boss, as in Fig. 2, which is a plan, and the
greater the speed the greater the lead, the dotted lines shewing that it may be
carried to a considerable extent. I do not confine myself to any particular
curvature of the parts; the cross section may, for instance, assume the form
Fig. 3, or the same may even be compounded of two straight lines as in
Fig. 4. The exterior part from 6 to c may also be radial, although I prefer
it to be angular, as shewn, and curvilinear, the latter more especially towards
the outer circumference, but in all cases the part from a to b should be angular
to the radius, and I prefer it curvilinear. The boss and blade will thus assume
in form and action several points of comparison with the breast and wing of a
bird, and the action will also present some analogy to that of a fish's tail. Any
number of blades may be employed.
My Invention consists, secondly, in an improved mode of feathering the
blades of propellers. The ordinary mode of feathering is by turning the blade
on a central pivot, and it has this objection that if the blade is a portion of a
true helix for a given pitch, it is no longer so when the pitch is altered. My
mode consists in constructing the propeller with a number of loose sections as
in Fig. 5, each section being furnished with as many arms or ribs as there
are blades; across the bearing sides of these arms is extended an elastic
substance, such as vulcanized india-rubber or elastic woven fabric, and they are
then opened out after the manner of a fan, and screwed or cottared firmly
together to the required pitch. By this means, to whatever extent the pitch
may be altered, it will always be a true one relatively at every part of the blade.
It is necessary in this case that the substance which lines the arms should
have tensional elasticity, but a substance which is only laterally flexible may be
employed, provided the arms themselves are elastic. In cases where there are
means of readily unshipping the screw, a number of sections can be stowed away
on board, and when desired a new screw can be quickly rigged out by merely
putting two or more sections together at the required angle, and stretching
across the arms strips of a flexible substance, such as gutta-percha, buffalo
hide, or stout canvass, and in this case I prefer to fit the boss of one section
into that of another, after the manner of Fig. 8, screwing or cottaring them
together when adjusted. Fig. 6 is a propeller of three sections thus con-
..
J

page_text: structed, and Fig. 7, a radial bladed one of two sections. The lining sub-
stance in all these cases may be attached in any convenient manner, but I
prefer to sew it with stout wire, holes being drilled in the arms for the purpose,
and the substance being protected where the wire passes through with metallic
ferrules or eyelets.