Ships – Method of sailing sailpowered watercraft
Reexamination Certificate
2000-01-12
2001-10-30
Basinger, Sherman (Department: 3617)
Ships
Method of sailing sailpowered watercraft
C701S021000
Reexamination Certificate
active
06308649
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the application of sensors to sailboats and recreational boating. Enhanced sailboat and crew performance is achieved through the use of new and existing sensors, data acquisition, computational analysis, graphical display and optional feedback control. The present invention covers the concept of a systems approach to measuring and optimizing sailboat and crew performance as well as the various sub-components, technology, software, algorithms and relationships that make up the implementation of such a system.
BACKGROUND OF THE INVENTION
The hydro-aerodynamic theory of sailing shows that optimizing sailboat performance is extremely complicated. There are also many complex inter-relationships between the many factors affecting sailboat performance. If we want to maximize boat speed (or other factor such as safety) External Factors such as wind speed, wind direction, variations in wind speed, variations in wind direction, and wave conditions will determine Optimum Setpoint Targets such as sail plan (size and type of sails used), sail shape, sail pressure distribution, boat heel, and rudder angle. In order to achieve these Optimum Setpoint Targets, various Control Variables such as forestay sag, mast bend, sheet tension, and halyard tension must be used. However, there is a complex inter-relationship between the Control Variables. For example both backstay tension and sheet tension will affect forestay sag which will affect the sail shape. Changes in mast bend will affect both jib and main sail shape.
In addition to the complex relationship between all of these variables, very small changes in a single variable may have an enormous effect on sailboat performance. For example,
FIG. 2
(taken from page 329, Aero-Hydrodynamics of Sails by Marchaj) shows the effect of sail draft depth (or camber) on sail pressure, holding all other variables constant under carefully controlled laboratory conditions. As can be seen, an increase in draft depth from 16.3% to 18.6% causes an increase in maximum pressure coefficient from 1.6 to 2.0 (while also reducing negative pressure on the windward side). This seemingly insignificant change in draft depth, which cannot even be measured on board a racing sailboat, causes a 25% increase in sail pressure! Since sail pressure is the driving force that moves a boat through the water, it is obvious that precise measurement and control of the draft depth is critical to optimizing the boat's performance.
While such laboratory experiments demonstrate that precise measurements are critical to optimizing sailboat performance, the data cannot be used in isolation on an actual boat. Many other factors and relationships must also be considered.
For simplicity in illustration, we may isolate the effect of wind speed on optimum sail shape. Small variations in wind speed have a large effect on optimum sail shape (e.g. draft depth and location . . . ) for a given sail. Furthermore, small variations in sail shape have a large effect on sail pressure and thus boat speed. These small and subtle changes are extremely difficult for the sailor to measure much less optimize.
For example, in a 4 knot wind the optimum draft depth for a given sail may be 10% and the optimum draft position may be 48%. In 8 knots the optimum may be 16% and 46%. In 12 knots the optimum may be 14% and 44%. In 18 knots the optimum may be 10% and 44%. However, in practice, it may be impossible for a sailor to measure by eye such subtle differences in draft depth and position even though such differences significantly affect boat speed. Furthermore; since wind direction, boat heel, rudder position, and other factors are constantly changing, it may be impossible for the sailor to even determine what the optimum sail shape should be, much less to measure what it is.
Some complexity may be added to this simple illustration. The optimum draft depth and position will vary from the foot to the head of both the jib and main sails, thus the sail twist must also be optimized. Also, rather than optimizing boat speed, we may optimize the “Velocity Made Good—Vmg” also known as Way Made Good (going fast toward the intended destination rather than just going fast). Finally, rather than looking at optimizing sail shape, we can look at the effect of changing one Control Variable, the sheeting angle.
FIG. 3
(from page 28, Aero-Hydrodynamics of Sails by Marchaj) shows the effect of sheeting angle (&dgr;m), wind speed (V
A
), and course heading (&bgr;) on Velocity Made Good (Vmg) under carefully controlled conditions in a wind tunnel. This shows that a wind speed increase from 10 to 14 knots requires a significant change in both boat heading and sheeting angle to maximize Velocity Made Good. At 10 knots (the second line from the left), the maximum is achieved at a heading of 25° and sheeting angle of 5°. At 14 knots (the third line from the left), the maximum requires a change to a heading of 29° and a sheeting angle of 14°. Failure to make the proper course and sheeting adjustments will result in a decrease in maximum velocity made good of over 10%. While such a minor adjustment is extremely difficult to detect, this could easily cost the race. A 12 minute difference over a 2 hour race is often the difference between first and last place!
This simple illustration shows two critical aspects addressed by the present invention. First of all, it is important, but difficult, to determine what the Optimum Target Setpoints should be. Secondly, it is important, but difficult, to measure small variations in Setpoints and Control Variables (e.g. sail shape and sheeting angle) that significantly affect the boat's performance. The present invention addresses both of these needs, providing accurate data and a means for determining and reproducing optimum sailing conditions.
There is relatively little prior art related to implementing a system that meets both these needs. On the one hand, there are prior inventions that fail to account for anywhere near the complexity of an actual racing sailboat. These prior inventions essentially tie a single sensor (such as wind direction or wind speed through the slot) to a single control variable (such as rudder angle or sail angle). Many of these prior inventions are mechanical attachments that automatically adjust for changes in wind direction in order to keep the boat headed in the right direction or keep the sails somewhat properly adjusted. None adequately account for the huge scale of complexity that is addressed by the present invention. In fact, very few of these types of prior inventions have found commercial use due to their very limited usefulness.
On the other hand, there is a limited body of literature that specifically addresses the aero-hydrodynamic theory of sailing. In these texts, cumbersome experiments are performed using wind tunnels and large sensors that are impractical for use in actual sailboat racing. For example, as recently as 1994 Lombardi and Tonelli published an experimental determination of the pressure distribution on a sail. They used liquid manometers connected by 1.5 mm diameter tubes to probes hung onto the sails. The fluctuations in liquid levels in these manometers were videotaped and then later replayed and manually transcribed to obtain the data desired. Obviously such a cumbersome system could never be used on a racing sailboat.
Another limitation with much of the present body of scientific literature is that the sailor cannot directly measure the data used by the theory. An example is shown in
FIGS. 4 and 5
. These figures show the desire to plot Apparent course (&bgr;) or true course (&ggr;) versus velocity made good (Vmg). However, the sailor cannot directly measure Vmg nor &ggr; nor &bgr;; he can only measure the boat speed V
S
and apparent wind direction (&bgr;−&lgr;). Another limitation is that the theories assume that the true wind direction is always constant and that the sailor's desired Vmg is always parallel to the true wind direction. This is no
Basinger Sherman
Leary James J.
Titus Carol D.
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