While the last few years have seen great advances made in the designs
of steamships and of their engines, little or nothing has been done in
the way of improving the screw propeller. As a general rule it would
appear to be taken for granted that no radical improvement could be
made in the form of the propeller, although various metals have been
introduced in its manufacture with the view of increasing its
efficiency. For sea-going steamers, however, the shape remains the
same, the variation chiefly relating to the number of blades employed.
A striking departure from ordinary practice, however, has of late been
made by Mr. B. Dickinson, who has invented a screw propeller which, on
practical trial, has given an efficiency far in advance of the
ordinary screw. This new propeller we illustrate here in Figs. C and
D, while Fig. A shows an ordinary propeller. The Dickinson propeller
illustrated has six blades, giving a surface of 30 square feet; it is
right handed, and has pitch of 15 ft. and a diameter of 10 ft. 6 in.
The ordinary screw propeller shown at Fig. A is right handed and two
bladed, with a pitch at the boss of 13 ft. 6 in. and at the tip of 15
ft. It has a diameter of 10 ft. 9 in. and 32 square ft. of surface.
The projected area looking forward is 22 square ft. and the projected
area looking athwartship 22.84 square feet. The most graphic way of
illustrating the principle of Mr. Dickinson's propeller is to take a
two bladed propeller of the ordinary type as shown at Fig. A in the
annexed cuts, and divide into three sections as in Fig. B, then move
section No. 1 to the line position on the shaft of No. 3, and No. 3 to
that of No. 1, No. 2 remaining stationary. The effect of this
interchange will be that (having regard to the circle of rotation) No.
3, the rearmost section, will rotate in advance of No. 2, and No. 2 in
advance of No. 1 (see Fig. C). By this arrangement the water operated
on escapes freely astern from every blade--that from No. 1 passing in
the wake of No. 2, while that from Nos. 2 and 1 passes in the wake of
No. 3. Fig. D represents the blades with a wider spread as practically
used. The advantages claimed by Mr. Dickinson for his propeller, and
which are sufficiently important to be given in detail, are:
[Illustration: Figs. A-D.]
1. That the blades of each section, when the vessel is in motion,
necessarily cut solid, undisturbed water, each blade operating upon
precisely the same quantity of water as an individual broad blade
would do, though, of course, it parts with it in one-third of the
time.
2. That each sectional blade exerts the equivalent efficiency of the
first or entering third portion of the breadth of an ordinary
propeller blade, and that consequently the combined sections have
greater effective power. It is now regarded by experts as an
ascertained fact that the after or trailing portion of the broad blade
is relatively non-effective as compared with the forward or entering
portion.
3. When three blades are fitted, the spent water from No. 2 being
delivered immediately in the wake of No. 3, and that from No. 1 in the
wake of No. 2, has the effect of destroying or reducing to a minimum
the back draught of sections Nos. 2 and 3, No. 1 alone being subject
to this drawback. This is of greater importance than might at first
thought appear, as in cases where there are three or four blades
revolving in one plane, the water is drawn after the retreating blade,
lessening the resistance to the face of the advancing one.
4. That by the subdivision of the blades, as arranged spirally, the
water passing through within the radius of the propeller has its
resisting capacity more thoroughly worked out than is possible with
any propeller whose blades are all on the same plane. This view is
confirmed by the visibly increased rotation of the water in the wake
of the vessel.
5. That by broadening the blades or increasing the number of sections,
the diameter of the propeller may be proportionately diminished
without the sacrifice of engine power. This is often desirable with
vessels of light draught, the complete immersion of the screw being at
all times necessary to avoid waste of power.
6. The propeller being made and fitted on the shaft in sections, all
that is necessary in case of accident is to replace the broken
section. This in many cases could be done afloat.
7. The blades being arranged to take their water at different planes,
there is the greater certainty of one or other of the sections
operating upon what is termed the water of friction. This is
considered an advantage.
8. Where it is desirable, the blades of the different sections can be
made of varying breadth or pitch.
9. The principle of division into two or more sections applies equally
to two, three, or four bladed ordinary propellers.
10. The adoption of this principle does not entail any alteration or
enlargement of the screw space or bay as usually provided.
11. As a consequence of the freedom and rapidity with which the water
operated upon escapes from the narrow blades, the depression at the
stern of the vessel caused by the action of the ordinary propeller is
greatly reduced.
12. The vibration caused by this propeller is so slight as to be
hardly noticeable, thereby effecting a saving in the wear and tear of
the engine and machinery. This may also be a consideration in
promoting the comfort of passengers.
From a practical and working point of view we take Mr. Dickinson's
chief claims to be, in the first place, the yielding of a greater
speed per power employed, or an economy in obtaining an equal speed;
in the second, increased, rapidity in maneuvering and stopping a
vessel; and in the third, a reduction of vibration. In order to put
these claims to a practical and reliable comparative test, Messrs.
Weatherley, Mead & Hussey, of Saint Dunstan's Hill, London, placed at
the inventor's disposal two of their new steamers, the Herongate and
the Belle of Dunkerque. These are in every respect sister boats, and
were built in 1887 by Messrs. Short Brothers, and engined by Mr. John
Dickinson, of Sunderland. The Herongate was fitted about four months
ago with the largest propeller yet made on Mr. B. Dickinson's
principle, the Belle of Dunkerque having an ordinary four-bladed
propeller of the latest improved type. Every precaution was taken to
place the two vessels on the same footing for the purpose of a
comparative test, which was recently carried out. Both vessels
previously to the trial were placed on the gridiron, cleaned and
painted, their boilers opened out and scaled, their steam gauges
independently tested, and both vessels loaded with a similar cargo of
pitch, the only difference being that the Herongate carried 11 tons
more dead weight and had one inch more mean draught than the Belle of
Dunkerque, while the former had been running continuously for nine
months against the latter's two and a half months. On the day of the
trial the vessels were lying in the Lower Hope reach, and it was
decided to run them over the measured mile there with equal pressure
of steam. The order of running having been arranged, the Herongate got
under way first, the Belle of Dunkerque following over the same
course. Steaming down against tide, the Herongate is said to have come
round with remarkable ease and rapidity, and in turning on either
helm, whether with or against tide, to have shown a decided advantage.
Equally manifest, it is stated, was the superiority shown in bringing
up the vessel by reversing, when running at full speed, thus
confirming the very favorable reports previously received by the
owners from their captains since the Dickinson propeller was fitted to
the Herongate. Those who were on board her state that the vibration
was scarcely noticeable. From a statement submitted to us it is clear
that the Herongate had the turn of the scale against her in dead
weight and draught, vacuum, and diagrams taken, but notwithstanding
(making allowance for one faulty run due to the variations in tide)
she appears to have more than held her own in the matter of speed,
with a saving of 4½ and 3¼ revolutions per minute at 140 lb. and 160
lb. steam pressure respectively. This is further confirmed by the
results of a run made after the experiments were concluded, the two
vessels being placed in line, and fairly started for a half hour's run
over the flood with 150 lb. steam pressure. At the expiration of that
time the Herongate was judged to be leading by at least half a length,
her revolutions being 76, as against 80 in the Belle of Dunkerque. It
was agreed by all present at these trials that the propeller had
realized in full the three main working advantages claimed for it.
This being the first Dickinson propeller fitted to a sea-going vessel
of this size, it is quite within the limits of possibility that the
present results may be improved upon in further practice. In any case
we can but regard this propeller as a distinct and original departure
in marine propulsion, and we congratulate Mr. Dickinson on his present
success and promising future. Messrs. Weatherley, Mead & Hussey also
deserve credit for their discernment, and for the spirited manner in
which they have taken up Mr. Dickinson's ingenious invention. We
understand that they are so satisfied with the results that they
intend having one of their larger ocean-going steamers fitted with the
Dickinson propeller.--_Iron_.
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