This report describes a patent concerning a device for measuring the speed of a surfboard or similar related to the water using the principle of deformations measurement by using strain gauges.

BACKGROUND OF THE INVENTION

Techniques have been developed for measuring the speed of vessels related to the water, but most of them are performed in laboratories.

In a laboratory the body stays still while the fluid flows around it. The measuring equipments used in these conditions only allow obtaining measurements to evaluate the body's hydrodynamic shape, resistance areas to the movement and friction losses.

In real conditions, measurements are not so simple and precise. There are only a few measuring equipments that when affixed to the surfboard do not significantly interfere on its performance, on the displacement resistance or even the surfer concentration. Patent PIO 106598-0 describes a telemetrical system for surfboard and correlatives.

It presents functional features and block diagrams for acquisition, transmission and storage the parameters with the data.

Other patents can be found describing systems for measuring boards' speed. Patent

GB2270504 describes a speed measuring system in knots, concerning a sailboard and applying the Venturi's tube principle. Patent DE19718917 describes a system that measures the board's speed by means of an optical system which detects the bubbles generated during the flow; the system, then, sends the data to an interface inside the wrist watch used by the surfer. Patent BR PI 0300620-4 published by WIPO under number

WO2004076990, describes a surfboard measuring speed system using a spherical lobe fixed to one of the ends of a stem. The water pressure force actuating on the sphere lobe

makes it and the stem swing related to a knee joint at the other end of the stem, enabling potentiometers to correlate the stem's displacement with the board's speed.

SUMMARY OF THE INVENTION

The device hereby described for measuring the speed of a surfboard differs from the above mentioned ones by presenting a system that measures the fluid flow speed related to a board or vessel by using string gauges. It has a stem with square cross-section perpendicularly affixed to the surfboard hull having a spherical lobe at the other end. The measurements are based on the solid stem's fibers expansion and contraction measuring principle and the stem's deformation values, measured by strain gauges, are digitally processed and transformed into parameters equal to the speed and the processor sending values corresponding to the fluid relative velocity related to the spherical lobe.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a side view of the measuring system affixed to the board hull showing the board(l) and the measuring system(2). Figure 2 is the measuring system(2) detailed view showing board(l), stem(3), sphere lobe(4) and strain gauges(5).

DESCRIPTION OF THE PREFERRED EMBODIMENT

Concerning the device hereby described it has the function of receiving the relative velocity of the board(l) related to the fluid, generally water. The device comprises a square cross-section stem(3) coated with a material providing a cylindrical external shape to it so as to undergo the lesser fluid flow resistance.

One of the ends of the stem(3) is affixed to the board(l) hull while the other holds the sphere lobe(4). Four strain gauges(5) are placed at approximately half the height of the stem(3), one on each stem's face.

The displacement water force applied on the sphere lobe(4) bends the stem(3) causing a deformation that can be measured by transducers like strain gauges(5). The strain gauges(5) are perpendicularly positioned one related to the other so as to form a disposition known as charge cell using Wheatstone bridge type electrical connection diagrams. This configuration allows simultaneously measuring the compressed fibers and the extended ones due to the bending strength of the stem(3) which values after processing the signal and being added of the time variable will result in speed and displacement of the board(l).

The strain gauges(5) measure the stem's longitudinal and transversal deformations related to the board(l); the achieved vectors, perpendicular among each other, are processed so as to achieve a resultant value. The processor searches, in a previously established table, for a value corresponding to the board's displacement speed. The measuring system(2) is previously calibrated in a laboratory where known measuring devices measure the water speed related to the board and simultaneously the strain gauges measure the deformations on the stem(3). This calibration table is added to the measuring system(2) micro controller processor. The obtained relative velocity value is then sent through radio frequency to fix digital stations and/or to a display on the surfer wrist.

The sphere lobe(4) that offers resistance to the water flow is an outstanding characteristic because the spherical shape offers equal resistance to the flow whichever is the water flow direction related to the board. So, it is possible to measure the board's displacement speed related to the water whichever the direction is.

The measuring system hereby described was said to be affixed to a surfboard only as an example of a real application and for a better understanding of the inventive act. It can be used, however, in other equipments and vehicles sliding on water, in the air or on any other fluid. The measuring system hereby described may be assembled to equipments

such as windsurf, kite surf, wakeboard or body board, boats or any other navigable vehicles.