Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a
modi~ication on a rudder for boats and ships~ com-
prising plates disposed on both sides of the rudder
and parallel with the rudder sur~aces. Many boats
have poor steering capabilities, especially at slow
speeds. This is particularly true for small boats,
such as the Norwegian "snekke" (a 16- to 24-foot open
fishing boat, pointed at both ends, most oEten
clinker built), and for other types of boats having
a relatively deep bottom, a long keel and driven by
an inboard motor, where the propeller turns about the
same axis at all times and thus cannot participate
in the steering. Such boats have especially poor
steering capabilities when reversing. In fact, some
boats do not answer the helm at all when reversing
at slow speeds. Some other boats can answer the helm
when reversing by turning only in the one direction.
It is obvious that this deficiency presents great
problems in situations in which precise manoevering
is required, for example, when sailing out of or into
a harbor or in other situations where it is necessary
to steer the ~raft while reversing. The problems with
such boats can be so grea-t that the owner of the boat
simply cannot risk taking his boat out of harbor if
the winds and sea are blowing toward land.
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The effect of a boat rudder is to deflect
the flow of water relative to the longitudinal
direction of the boat whether this flow results from
the speed of the boat or from water which has been set
in motion by the screw. The propeller flow, however,
is far from laminar, and it therefore has a rela-tively
bad effect on the steering of -the boat. Therefore,
a boat travelling at slow speed will have poorer
steering than the same boat travelling at higher
speeds. In some cases, the screw will reduce the
steering properties of the boat. This is particularly
true when reversing, because the laminar flow of water
which moves along the hull of the boat wil~ be broken
up by the prope]ler, which has poor screw properties
when reversing, the blades cf a propeller being con-
stru~ted first and foremost with forward propulsion in
mind. On boats which have poor steering capabilities
in reverse, thereforer one must often set the boat in
motion backwards and then cut out the propeller before
the rudder will have any steering effect.
Several different types of aids have been
tried in attempts to improve the steering properties
of boats of the above type. Thus, various '-ypes of
: guide plates on both sides of the rudder surface have
been tried.
A modification on a rudder is known from Norwegian
patent No. 59~795, in which plates tha-t are parallel with
the rudder surface are provided on each side of -the rudder,
the leading edge of -the pla-tes projecting forward of the
middle leading edge of -the rudder. The primary object of
this modification is to balance the rudder, in -that one
thereby obtains steering surfaces which lie in fron-t of the
rudder shaft. A similar modification is ]~nown from ~.S.
pa-tent No. 3,181,492.
It is known from U.S. pa-tent No. 2,328,04]. to
mount arch-shaped guide wings on both sides of a conven-
tional plate rudder in such a manner -tha-t the guide wings
are disposed radially exterior of the propeller when -the
rudder is in the neutral position.
However, the modi.fications of -this type known
hitherto have not had the desired effect, and at present
no effective aid exis-ts for increasing or improving the
steering capabilities, especially when reversing, on boats
: of the type defined above.
The presen-t invention is to provide for the modi-
fication of a rudder for boa-ts and ships which comprises
plates di.sposed on both sides
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of the rudder and parallel with the rudder surfaces which
improves the steering properties of the boat both when rev-
ersing and during forward propulsion.
~ccording to the present invention there is pro-
vided in a rudder arrangement for boats and ships, compris-
ing a channel of substantially circular cross-section which
is disposed rearwardly and coaxially of the propeller and
which is rotatable about a substantially vertical axis, the
walls of said channel at the rearward end thereof being pro-
vided with two V-shaped notches with the respective apices
of the notches lying on a central vertical plane extending
through the channel so as to form an arched tongue on both
sides of said plane, the improvement in which the front edge
of said channel is spaced from the propeller plane so as not
to intersect said plane in any rudder position, and the two
arched tongues are immovable relative to one another and
extend parallel to one another both on forward motion and
reversing motion of the boat or ship, in which reversing
motion the mo-tor propeller of the boat or ship is in reverse
rotation, so as to provide increased steering capabilities
for the boat or ship, both on said forward and reversing
motion.
Numerous trials have been shown that this configura-
tion of a channel-shaped rudder provides quite superior steer-
ing properties, especially when reversing. This is very
important, as reversing with boats have a pointed bottom
configuration, such as the Norwegian "snekke" fishing boat,
has always been problematic. With a rudder having the con-
figuration defined above, such a boat will answer the helm
equally well in both directions, while it
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would normally answer the helm only in the direction of
rotation for the propeller. The steering properties of the
boat will also be improved in the forward direction,
especially when moving forward at very slow speeds.
According to a preferred embodimen-t of the inven-
tion -the tongues constitute approximately one-half of the
total length of the channel in the longitudinal direction
of the boat.
A special embodiment of -the invention is charac
terized in that the channel is arranged in combination with
a plate-type rudder, the channel being arranyed symmetri-
cally on both sides of the rudder plate. Such an arrange-
ment will be practical for a boa-t which is equipped with a
conventional plate rudder, as it permits one to attach a
half-sec-tion of the channel on each side of the rudder.
The invention will be elucida-ted further in the
following with reference to the accompanying drawings,
which illustrate two different embodiments of the invention.
Figure 1 shows a first embodiment of a rudder
according to the inven-tion, mounted on a small boat, in
perspective, and
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Figure 2 shows the same embodiment seen
directly from ~bove.
Figure 3 shows a second embodiment of
the rudder according to the invention, in perspective,
a~d
Figu,res 4 and 5 show the embodiment
of Figure 3 seen straight from the back and directly
from above, respectively.
In accordance with the embodiment
illustrated in Figure 1, a circular, channel-shape~d
rudder 1 i5 provided between the stern 2 of the boat
and a lower rudder support 3. The rearwardly-
pro~ecting support 3 is -the most common construction
on small boats, but one also finds types of boats
in which this support is not present, in which case
the rudder is supported solely by the rudder post ~.
The boat illustrated in this example is driven by
a three-blade screw with reversible directions of
rotation. The rudder shaft 4 is attached to the
channel 1 forwar~ of the middle of the total length
L of the channel. Two V-shaped notches have been cut
into the ~ at its rearward end, the -tip~of each
V lying in the central vertical plane through the
channel 1. In this manner, respective arch-shaped
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tongl1es 7,8 are formed on each slde of said plane,
the total length a of the tongues in the longitudinal
direction of the channel being approximately equal to
one-half the -total length L of the channel.
Figure 3 shows an embodiment which is
well suited for rebuilding the rudder of a boat which
is already equipped with a conventional plate rudder
9, placed between the stern 2 of the boat and the
lower support 3. In this example, also the boat
is driven by a three-blade screw 5 with reversible
directions of rotation. The rudder is rotated by
means of a rudder shaft 4, which is placed a
distance behind the leading edge of the ruddex plate
9 in order to obtain a certain balancing effect.
Attached to both flat sides of the rudder 9 are
arched guide plates 11 and 12. The curvature of
the plates is in accordance with a circular line in
the crosswise direction of the boat, such that the
two plates 11,12 together form a circular~shaped
channel. The lateral marginal edges 13 of the
plates 11,12 ~Figure 5) are parallel with one another
and with the rudder surface on the plate rudder 9.
The plates 11 and 12 are attached at their upper and
1ower edges 14 and 15 to the respective upper and
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lower edges oE the rudder surface. The forward edge
on the plates 11,12 is disposed somewhat astern
of the rudder shaft 4. The plates 11,12 have a
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curved rearward edge 'n~, such that the outer
marginal edges 13 of the plate project somewhat
astern of the plate parts, which are attached to the
rudder at 14 and 15. In this way, tongues or overhangs
17 are formed~
The diameter of the channel which is
formed by the two plates 11 and 12 is larger than
the screw diameter of the propeller 5. In regard
to the dimensions of the plates 11 and 12, the length
a of the o~erhang 17 is approximately equal to the
remaining length h of the total length L (see
Figure 5) t i.e., the length a of the overhang 17
is approximately equal to one-half of the total
length of the plates 11 or 12. The ratio of the
length L (=a ~ b~ to the diameter lies between 3~4
and 3:6.
A rudder modification in accordance
with the exemplified embodiments was tested on a
small fishing boat which had extremely poor steering
properties, especially when reversing. At slow
speeds, this "snekke" boat did not answer the helm
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at all in one direction during a reversing operation.
The boat's berth was situated such that the sea and
wind often blew toward land, and it often happenea
that the owner could not take his boat out for the
sole reason that it was not sufficiently manoeverable,
as it was impossible to steer the boat in reverse.
After the modification according to the invention was
installed, the owner claimed that the boat was as
easy to steer as an automobile, and that it answered
the helm when driven in reverse both at slow speeds
and at full speed. In addition, the turn radius
during forward propulsion had also become substantially
smaller.
Another effect of the modification
according to the invention is that it also prevents
or greatly reduces the downward drag on the stern end
of boats of this type. This is a common phenomenon,
and it reduces speed or increases fuel consumption
rather significantly. In order to preven-t this,
some boats have a hull built with an expensive
support plane or support fins in the region of the
screw. Such hull modifications can be rendered un-
necessary with the use of the invention, and the
price of the hull correspondingly reduced.
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