IMPROVEMENTS IN INSTRUMENTS FOR ASCERTAINING THE PITCH OF SCREW PROPELLORS."
Year: 1881

page_text: LETTERS PATENT to David Brown Hutton, of Poplar, in the County of
Middlesex, Engineer, for an Invention of "IMPROVEMENTS IN INSTRUMENTS
FOR ASCERTAINING THE PITCH OF SCREW PROPELLORS."
PROVISIONAL SPECIFICATION left by the said David Brown Hutton at
the Office of the Commissioners of Patents on the 16th December 1881.
DAVID BROWN HUTTON of Poplar in the County of Middlesex, Engineer.
"IMPROVEMENTS IN INSTRUMENTS FOR
ASCERTAINING THE PITCH OF SCREW
PROPELLORS."
Great difficulty is at present experienced in ascertaining the true pitch of screw
propellors and clumsy and inefficient appliances are generally employed for the
purpose.
Now my improved instrument is for taking the pitch of propellor blades by
forming a right angled triangle on any required part of the diameter by means of
the said instrument. It is constructed with two movable legs jointed together and
having their inner edges starting from one common centre; on one leg, which may
be called the diameter line, and preferably at or near its extremity farthest from
the main joint is jointed a spirit level plummet, or equivalent which gives the
true fore and aft (horizontal) line. This leg is divided into a scale of parts and
marked for convenience in diameters of the pitch circles though actually the
distances on the scale represent the circumferences of circles due to these diameters.
A movable slide with a folding arm divided to the same scale can be moved along
this leg or diameter line and may be designated the "pitch-arm." The diameter
line leg may be slotted to receive the slide or the slide may be formed like a sleevo
to slide upon it. The "pitch line" urin is so arranged that a stop prevents its
passing a right angle with the diameter line leg so that when fully opened it
always stands at a right angle thereto. The edges of the two legs should be
parallel with each other when closed.
In use this instrument is placed against the boss of the propellor and the level
adjusted; it is next placed upon the blade at any known diameter which may be

page_text: marked upon the blade beforehand and the diameter line leg opened out till the
level assumes the same position as when adjusted on the boss. The pitch line
arm is now moved along the leg to the division corresponding with the diameter
upon the blade at which the angle was obtained by opening out the legs and folded
across until arrested by the stop when the line where the inner edge of the other
leg crosses it is the correct pitch.
This instrument may also be employed for pitching spare or shifting blades.
A wing and thumbscrew or equivalent device may be employed to fix the legs
A similar device can also, if
when set; or a stiff' joint, but this is not reliable.
desired be used for the level, but a stiff joint I find to answer well in this case for
general purposes.
One instrument which I have made is constructed mostly of hard wood with
brass ends and joints and it answers well, but for regular use I prefer metal, say
steel, on account of its strength lightness and hardness as the edges must be kept
as true as possible. However it is evident that various materials may be used for
these instruments. The one I have made is divided to a scale of 1/2 inch to the
foot and I find this a very convenient size to work with; I do not however bind
myself to this one scale as others will give just as correct results the difference
being that the instrument will be larger or smaller according to the scale
employed.
It will be noticed that this improved instrument can be used for blades of
increasing pitch.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said David Brown Hutton in the Great Seal Patent Office on the
16th June 1882.
<<
DAVID BROWN HUTTON of Poplar in the County of Middlesex, Engineer.
'IMPROVEMENTS IN INSTRUMENTS FOR ASCERTAINING THE PITCH OF SCREW
PROPELLORS."
Great difficulty is at present experienced in ascertaining the true pitch of screw
propellors and clumsy and inefficient appliances are generally employed for tho
purpose.
Now my improved instrument is for taking the pitch of propellor blades by
forming a right angled triangle at any required diaineter by means of the said
instrument. It is constructed with two movable legs jointed together and having
their inner edges starting from one common centre; on one leg which may be called
the diameter line and preferably at or near its extremity farthest from the main
joint is jointed a spirit level plummet or equivalent, which gives the true fore and
aft (horizontal) line. This leg is divided into a scale of parts and marked for
convenience in diameters of the pitch circles though actually the distances on the
scale represent the circumferences of circles due to these diameters. A movable
slide with a folding arm divided to the same scale can be moved along this leg or
diameter line and may be designated the "pitch arm."
The diameter line leg may
be slotted to receive the slide or the slide may be formed like a sleeve to slide
upon it. The "pitch line" arm is so arranged that a stop prevents its passing a
right angle with the diameter line leg so that when fully opened it always stands
at a right angle thereto. The edges of the two legs should be parallel with each
other when closed.
In the accompanying Drawing the instrument is represented about one third of
its ordinary size. A is the diameter line leg B the hypothenuse line leg, and C the
pitch line arm. A and B are jointed by a strong and carefully fitted joint at D
and a wing and thumbscrew E is provided for fixing them at the required angle,
F is the spirit level capable of being turned upon a stiff joint and pin F1 for
adjustment and convenience of stowage. Instead of the spirit level a pluminet or
equivalent can of course be used if preferred as either of them will give a datum
from which to work. The arm C is jointed at C' to a slide or sleeve G so that it
can be moved along the leg A as required or folded up out of the way a stop a¹
upon the sleeve or arm prevents it from passing a right angle when opened fully
out. The leg A is shown with a long slot in it but could be made solid if preferred.
The scales should be set off by machinery to ensure great accuracy; and the edges
should be truly parallel.
The spaces upon the leg A are proportioned to the circumferences of circles whose
diameters are indicated by the Figures marked at such spaces, thus (supposing the
instrument to be for convenience made on the scale of inch to the foot) the
Figure 1 represents one foot of diameter of the propellor but the space from the
centre of the joint D to the Figure 1 is really 3.14159 times one foot being actually
(at the above mentioned scale of inch to the foot) 1.570795 inches from the centre
of D. This will be readily understood when it is remembered that the base of the
triangle (the arm C) represents a line upon the circumference of a circle of the
diameter at which the pitch is being taken and the leg A is therefore really
graduated to circumferences although for convenience they are called diameters.
The second line is a like distance from the first and the leg can be graduated to
any desired extent; in the Drawing it is shown graduated only to 20 feet but this
could be increased by increasing the size of the iustrument. It will be observed
that the Drawing is represented a good deal smaller than the sizes given above it
is really about of those sizes; and it must be understood that the inch scale is
given only as a convenient size for the instrument and there is no impossibility in

page_text: making it 3 inch or 6 inch scale or even full size, but it would in that case be a
most unwieldy instrument if it were graduated to suit propellors of large size.
Similarly a smaller scale than inch to the foot can be employed if desired.
The leg B is not graduated at all; it serves to form the hypothenuse of the
triangle and is placed in contact with the propellor blade when taking the pitch
etecteru.
The arm C forms the base of the triangle and represents the pitch line of the
propellor and is graduated to the same scale as leg A.
To ascertain the pitch of a propellor the legs A and B are closed up and placed
vertically against the end of the propellor boss and the level adjusted. A line is
marked across the propellor blade at the diameter at which the pitch is to be
taken and leg B laid across it and held, whilst leg A is opened out until the level F
as adjusted becomes horizontal when the thumb screw is tightened up and the
legs fixed at that angle. The arm C is now opened out and run up until it reaches
the same diameter upon a A as that at which the pitch is to be taken and the
operation is completed. According to the position in the Drawing the pitch has
been taken at a diameter of 12 feet (the position occupied by C upon leg A) and
the pitch is just under 13 feet as shown by the point where the inner edge of B
(hypothenuse line) crosses arm C.
The in-trument may also be used for adjusting and making centre lines on spare
blades where the required pitch to be given is known but not the proper angle
or centre line at which the blade must be attached to the boss.
It is also very
useful in a variety of ways particularly at sea as a straight edge or with loose
ends to slip on it forms a pair of trammels or compasses.
Various materials may be employed in its construction but steel with brass
“fittings are about the most useful.
Having now described my Invention and the method of performing the same I
wish it to be understood that I do not broadly claim the principle of ascertaining
the pitch of screw propellors by means of an instrument, but that what I do claim
and desire to protect by Letters Patent is :-
1. The instrument substantially as herein described and illustrated consisting
essentially of legs A and B and arm C capable of forming respectively the perpen-
dicular the hypothenuse and the base of a right angled triangle inverted or
otherwise and provided with a spirit level plummet or equivalent whereby the
pitch of a propellor blade at any given diameter may be determined.
2. The leg A graduated as herein before set forth, the scale indicating the
diameters by which to set or adjust the arm C and the leg itself serving as the
perpendicular of a right angled triangle substantially as and for the purposes set
forth and shewn.
3. The arm C graduated as described jointed to a sleeve or equivalent G so as
to be capable of being moved upon leg A or folded over upon it, a suitable stop
being preferably provided to prevent arm C from passing beyond a right angle
with leg A when opened fully out substantially as and for the purposes set forth
and shown.
4. The employment of a spirit level plummet or equivalent in combination with
the herein described instrument for the purposes and in the manner substantially
as set forth.
In witness whercof I the said David Brown Hutton have hereunto set my
hand and seal this Thirteenth day of June in the year of our Lord One
thousand eight hundred and eighty two.
DAVID BROWN HUTTON. (L.S.)