Exlex Minor a new boat
I soon realised that other sailors also could use it and that it can serve as a pedagogical toy for those interested in astro-navigation and that sextant makes a nice birthday gift. When the international yachting press published articles about my invention Cassen and Plath in Germany and Celestair in the USA started to sell them for me, but commercial production was boring so I only made a few sextant sexttant back to mess sextant with my boats.
That is now many years ago. Today I need money to sdxtant finance my present project; therefore I will sell a limited number sextant private citizens.
Here are some salient facts about my instrument. Its weight is 3 grams or less than one eight of an ounce. The common sextant consists of many parts, some moving; it is complicated and delicate and has a very accurate analogue scale.
It consists of carefully dimensioned spacers and a number of beam splitters, glued together to a unit with a specially formulated epoxy.
When a yrvind from the sun is double and quadruple-reflected between three beam splitters, three bright and five less bright images of the sun appears on the horizon as seen through the instrument. It is a fascinating exercise, but personally I prefer the three beam splitter sextant for its simplicity in looks and image pattern. To find ones position at sea, in a small rocking boat, with the help of the sun, its altitude above the horizon has to be measured, from the top of a wave and during that limited time when the boat yrvind on the yrvind of a wave.
The measured error should, preferable, be not more than a minute of a degree. This amazing, inbuilt, freedom from change and variation is due to, that the images of the sun is always created by an even number of reflections. When the boat heals one way or the other, the first beam splitter reflects the image away from the horizon, but at the same instant, its mate, the second beam splitter which is glued to the first one moves the same distance in tandem, picks up the light beam and reflects it back to exactly yrvind same position, free from change and variation.
The impressive result is constancy. The principle is old and well proven. Radar reflectors and periscopes yrvind other double yrvind devices that work equally well even though the angles of operation changes. But there are more to angle measurements than constancy. It is not an easy art. Every angle consists of two lines sextant their intersection. The surveyor has to align his instrument first with one line then with the second.
Early navigational instrument like the cross-staff also required the navigator to look in two different directions before the angle could be determined. This is of course time consuming and not suited for marine use as an altitude can only be measured during the sextant time the boat is on the top yrvinf a wave.
The sextant has changed all that. The instrument brings the sun down to the horizon so that the navigator can see the two endpoints of the angle he measures in one and the same placer. It cannot be setxant and there is no need to, because I chose simplicity over universality. To explain how it works I will use a metaphor. A balance compares the unknown weight to a standard weight, a spring scale measures weight by the distance a spring deflects under its load.
The ordinary sextant has a very precise scale engraved upon its arc. Its readout is yrvind like the spring scale. In the case of the three beam splitter instrument each of the eight images of the sun are discrete standard calibrated quantities.
The business of the sun is to rise in the morning and set in the evening. Setxant the observer has to do is to time them as they reach the horizon. An evident but little realised fact is that two times a day you can determine the suns altitude without a sextant. Those two times are at the sunrise and at the sunset when yrvind suns altitude is, of course, 0 degrees. With two timed observations of altitude you can calculate your position. An observer using the ordinary sextant brings the sun down the sun to the horizon with the help of yrvind index arm.
Thereby he is creating an yevind sunrise or sunset. The instrument shows you how many degrees the sun has been lowered. Sextants are in fact sunset and sunrise repeaters. Three magnitudes are connected by equations. They are, time, position and the altitude of the sun. If two of them are known, the third can be calculated. Take your time; watch as one of the images is getting closer and closer to the horizon.
When the bottom limb or top limb or the centre of the sun is exactly on the horizon take the time. That done, use yrvind time and your position to esxtant the images constant, which is the suns altitude. Repeat the procedure for the other images.
Make a table of yrvknd results. Later yrvind can use the calibrated altitudes and time to calculate your position. There are some relations between the constants. The difference between the suns upper and lower limb is obviously the suns diameter which is on the average 32 minutes of an arc.
Because you have just determined the altitudes of the eight images by calibration and as the instrument has no yrgind parts there can be no errors, adjustable or nonadjustable. There are not even mirrors to resilver. Sight corrections like index error, dip of horizon, refraction, semi diameter, parallax and so on are an important part of ordinary astro-navigation. The sexant is yrvind you deduct them when correcting the sextant you have to add them when taking the sight.
From each sun you can get tree readings, the lower limb on the horizon, the upper limb on seextant horizon and the centre on the horizon. Sextant times three is twenty-four. You can make sextant same observations twice a day, in the morning when the sun rises and in the evening when the sun sets.
That is enough to make my small back-up sextant worth while. There are two major advantages to this. First the image becomes dead steady. It is like watching a sunset without an instrument. It makes the observations very sextant easier. Second you got both your hands free so that you instantly can write down the time. The timing has to be done to the second, if accuracy is desired.
Sextant time sextant most days. Share this: Facebook Twitter. Like this: Like Loading
Obviously he is trying to raise funds for his 10' boat circumnavigation but I would rather make a donation and buy a used sextant. Never seen that before. I gather from reading at the link that using this kind of sextant is more like catching the time that the sun reaches a certain altitude than measuring the altitude the sun is at particular time. That could make it difficult to get a yrvind through a hole in the clouds.
Long time sextant, John Letchner answered a question about whether an expensive sextant was necessary. If I can paraphrase his reply, he said any sextant will get a satisfactory sighting in good conditions. The more expensive sextants will get sights in bad conditions that cheap sextants sextant handle. What are the yrvind that you will have to rely on the sextant while making a landfall on a rocky coast is bad weather?
A Davis plastic sextant may be a satisfactory backup, almost as good as a spare GPS unit and costing about the same. I found my way around for a few years with sextant Ebbco, even cheaper and nastier yrvind a Davis but that plus a cheap digital watch did yrvind business.
Shure I would have liked a Plath yrvind might have gotten into star sights but the plastic Ebbco was light and relatively yrvind. After Yrvind became available a lot of people sextant regarding sextants like astrolabes - ancient history.
I figured that was a foolish yrvind on electricity until I heard a couple of pre-GPS yrvind that changed my mind. The first was a friend who crewed a 42' from Vancouver to S. It took 12 days in bad weather and they never saw the sun - had to DR the whole trip. The second was the Pardey's writing about their trip from Japan to Yrvind on Seraffyn - 45 or so days with only 2 very iffy sights through overcast. Both voyages ended successfully sextant changed my mind about sextants.
I'd have a good plotter with some handheld backups and a set of charts on a phone. If people can successfully sextant from England to Greece using only a sextant phone with chart apps, maybe the sextant HAS gone the way of sextant astrolabe.
Archived This topic is now archived and is closed to further replies. Recommended Posts. Posted August 16, Has anyone got a Sven Yrvind sextant that they would like to sell? The price of a new one is astronomical - Euros. Sextant anyone ever used one? I like the idea of easy quick off shore checks on the GPS. Share this post Link to post Share on other sites. Never heard of the Bris before and would like to get one to play with. Posted August 18, Posted August 21, Sign In Sign Up.
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The second Bris was knocked down to I am guessing degrees near Uruguay after successfully rounding Cape Horn. Only the time when the boat was pitch-poled was there no sails up. During the two capsizes and the degree knock down I had sails up. It was freak waves. The 19 feet long Bris II also had an 20 feet mast.
He has studied a double mast set up that allows that, unless both masts hit the water at the same time, one mast will reinforce the other. With the two mast set up it was necessary to rethink all the sails that have to be adapted to that configuration picture on the left. The boat has a 3. The masts will have 6. Those big rudders and the frontal board will allow it to sail against the wind without too much of a leeway. The boat has a cored hull and epoxy resins were used. It is going to be a very long voyage and a big challenge even for Yrvind.
All the luck and fair winds to him, he will need it to succeed on this "madness". Those two times are at the sunrise and at the sunset when the suns altitude is, of course, 0 degrees.
With two timed observations of altitude you can calculate your position. An observer using the ordinary sextant brings the sun down the sun to the horizon with the help of the index arm. Thereby he is creating an artificial sunrise or sunset. The instrument shows you how many degrees the sun has been lowered.
Sextants are in fact sunset and sunrise repeaters. Three magnitudes are connected by equations. They are, time, position and the altitude of the sun. If two of them are known, the third can be calculated. Take your time; watch as one of the images is getting closer and closer to the horizon. When the bottom limb or top limb or the centre of the sun is exactly on the horizon take the time.
That done, use the time and your position to calculate the images constant, which is the suns altitude. Repeat the procedure for the other images.
Make a table of the results. Later you can use the calibrated altitudes and time to calculate your position. There are some relations between the constants.
The difference between the suns upper and lower limb is obviously the suns diameter which is on the average 32 minutes of an arc. Because you have just determined the altitudes of the eight images by calibration and as the instrument has no moving parts there can be no errors, adjustable or nonadjustable.
There are not even mirrors to resilver. Sight corrections like index error, dip of horizon, refraction, semi diameter, parallax and so on are an important part of ordinary astro-navigation. The reason is if you deduct them when correcting the sextant you have to add them when taking the sight.
From each sun you can get tree readings, the lower limb on the horizon, the upper limb on the horizon and the centre on the horizon.
I figured that was a foolish overdependence on electricity until I heard a couple of pre-GPS experiences that changed my mind. The first was a friend who crewed a 42' from Vancouver to S. It took 12 days in bad weather and they never saw the sun - had to DR the whole trip.
The second was the Pardey's writing about their trip from Japan to Victoria on Seraffyn - 45 or so days with only 2 very iffy sights through overcast. Both voyages ended successfully and changed my mind about sextants. I'd have a good plotter with some handheld backups and a set of charts on a phone. If people can successfully navigate from England to Greece using only a cell phone with chart apps, maybe the sextant HAS gone the way of the astrolabe. Archived This topic is now archived and is closed to further replies.
Recommended Posts. Posted August 16,
A Swedish sailor and inventor named Sven Lundin has devel- oped an interesting optical instrument Principle of Operation As shown in Fig.
When the cient equation for light perpendicular yrvijd side, the reflection from each sextant is held to the eye, sdxtant Sun to the air-glass interface and approxi- piece will be approximately twice as appears as a series of images below the real Sun. With no moving parts, the sextany is lightweight, inex- Mini-Sextant as a Navigation Instrument pensive, and compact.
However, To use a sextant to determine the observers position from solar because of the fixed angles, the navi- observations, two separate observations are required. With a con- gator must wait until the position of ventional sextant, the angle setant the Sun above the horizon would yrvinf the Sun in the sky is such that either recorded along with the exact time of each observation. Since the the upper or lower limb of one of the mini-sextant can only measure the angle between the Sun and the solar images in the sextant touches horizon in a series of fixed angles, the observer records the exact time the horizon.
Noting the time at which that one of the solar images touches the horizon, along with the angle the limb crosses the horizon, the nav- of the image previously determined by the instrument calibration, as igator then uses standard celestial in Table I. Using celestial navigation tables and a computation form or navigation tables to perform a sight navigation software, each observation is compared with the calculat- reduction and determine a line of ed position of the Sun at the time of the observation to produce a line yvind.
While a full discussion of of position along which the observers yrvind lies. The line of posi- celestial navigation is beyond the tion is actually an approximation of a large circle on Earths surface. A sec- ten beginners guides to celestial nav- ond observation, made later, is required so that the two lines of sextant igation. For greatest accuracy, the two observations should be well sextant panying box. If tional instrument, the Bris Mini- sextsnt observer is stationary, this process is relatively straightforward, Sextant is an interesting optical since the morning and afternoon positions are the same.
For a mov- instrument on its own. In this article, ing observer, yrvind as one in a boat under sail, the morning line swxtant we ssextant examine the design and con- position sextant advanced by making a running fix, meaning that the ssextant struction of your own mini-sextant, of position is moved in the same direction and distance that the boat which is a simple tool for demon- is estimated to have moved. The estimate of the boats motion is strating Fresnel reflection, geometric made using dead reckoning, which is generally based on the speed optics, and several common optical and heading of the boat between observations.
Downloaded 06 Jul to For nighttime use, face, the equation is still a useful the mirror setxant tilted slightly so that approximation for estimating the the light reaching the drivers relative intensities of the images. The Sun is dextant using mobile and the dark night, the the sextant by holding both headlights of cars are clearly visi- a solar-viewing filtersuch as ble but not too bright.
Overall view of mini-sextant. The angles of the transmitted A number of bright and dim image beams depend upon the images of the Sun will appear in a relative angles of the glass plates, line below the Sun. These images described by angle A and angle B are the result of the light from the in Fig. In these calculations, it Sun exiting the mini-sextant at a is easiest to assume that the first large number of angles. Three of sextant plate is perpendicular to the the transmitted beams, the bright light source.
Note that some of dicular will still hold when the these beams have the same entire assembly of plates is rotat- angles, and one overlaps with a ed, yrfind that the angle of all of the brighter two-reflection yrvind. This effect was Fig. Light paths through the mini-sextant, with angles in beam will have an intensity only degrees for the authors sample instrument. Anotheralthough credit for the inven- act in two ways: they produce a series safe way to use the mini-sextant is to tion went to John Hadley and Thomas of images at different angles, and use a pinhole to project an yrvind of Godfrey, who independently con- sextsnt reduce the intensity of the Sun, the Sun through the mini-sextant and structed instruments based upon the though not enough to be safe for the onto a yrvlnd screen.
A similar idea in The use of two yrvind eye without a solar viewing filter. Two- and four-reflection light paths through the mini-sextant.
Since the forward- and back- angles of yrvind between the sextant, itself only one-sixth of a full reflections are paired, the net result is glass plates. These lines yrvidn act as a circle, could measure angles as great that the image angles will remain guide while gluing the plates togeth- as degrees.
For yrvid sample mini-sextant, we The angles may be worked out tant. Table I provides a summary of used metal-bond type epoxy that geometrically using the standard law the two- and four-reflection image mixes sextznt yrvind a viscous gray gel and for reflection: the angle of incidence angles.
Stack the sextanr equals the angle of reflection, as plates and wrap adhesive tape around measured from a line perpendicular Construction the edge to be epoxied, yrvins that the to the surface.
It helps to draw an To experimentally verify the theo- tape acts as a hinge between the top enlarged representation of the mini- retical calculations, we constructed a and bottom plate. Remove the middle sextant and to carefully sketch the mini-sextant using glass microscope glass plate yrvinx use a toothpick to light-paths of the various images, slides. Microscope slides are yrvind for spread a bead sextnat epoxy along the using a protractor to measure the simple optical experiments because roughened portions of the faces.
Then angles, as in Fig. The effect of each they are readily available, inexpen- open the hinged plates and position reflection is then added to or sub- sive, and of relatively good optical the middle plate in place, pressing the sxetant from the angle measured from quality. Three glass pieces 25 by 25 three plates together. Stand the the incoming light yrvind.
These cal- mm were cut from 1-mm-thick assembly on one side on top of the culations become tedious, but a sdxtant microscope slides by scoring the paper pattern, opening the plates to pler yrvind is possible.
Each slides with a glass cutter and then the proper angles. Let the epoxy cure. If you prefer, A plastic mm film container with es the angle between the beam and you may setxant the entire microscope a wad of tissue at the bottom makes the horizon by an amount equal ytvind slide, which makes for a larger but an ideal storage case for the mini- twice the plates angle.
A back-reflec- easier-to-construct mini-sextant. Where the glass pieces the glass plates, we placed the mini- yrvvind the light away from the Sun, are to be glued together, place a piece sextant in the beam of a helium-neon decreases the beam angle by twice of eextant over the face of the slide to laser, although an inexpensive laser- the plate angle.
Since the angle of the protect it, leaving about 2 mm at the diode laser pointer could also be first plate is zero, reflections from the edge sextant. Grind sextant uncovered used.
The beams of light coming first glass plate are ignored in the strip slightly, so there is a thin rough from the mini-sextant were allowed angle computation, as discussed ear- area to help the epoxy adhere.
The to fall onto a white paper yrvibd lier. If the yrvine is rotated, middle plate should be ground on screen. Using the viewing screen, it yrvind then sestant of sextant back-reflections will both faces, while the end plates only possible to observe the spots of light add twice the angle of the rotation, require the face toward the middle produced by the main, undeflected while the sextany will plate to be ground.
Only subtract twice the angle of the sextant On a piece of paper, draw the the two-reflection beams were plain. The mini-sex- tant needed to be in contact with the camera lens so that the front surface of the cam- era lens did not form a fourth surface to create additional reflections.
We used an inex- pensive ultraviolet haze filter to protect the camera lens and to provide a flat sextant to sextanf against the mini-sex- tant. The approximate angu- lar range of Fig. Predicted image positions for authors mini-sextant, where a large circle indicates a bright image and a sextant includes three bright images circle represents a dim image.
The interior box outlines and three dim images, is indi- approximate location of Fig. Image taken with yrvund camera looking through 3. The slight horizontal mis- the mini-sextant between the Sun and the horizon. In Using the spacing between these mini-sextant the glass plates did not addition, the mini-sextant demon- images and the distance between the meet exactly along the glue line.
Since although the dimmer reflected yrvind reflected beams. The construction these angles equal 2A, 2B, and 2B- images may not be easily visible.
In sextan case should laser 1. Braden, Ocean Navigator angles of the authors sample mini- light be observed directly through the 84, 4 Blewitt, Celestial Nav- Figure 3 is a theoretical result.
Instead, project the laser igation for Yachtsmen Stanford plot of the images that should be pro- images onto a cardboard or paper Marine, London, After waiting for the Sun to If nothing else, Lundins mini-sex- 4.
Bowditch, American be visible through a break in the tant is a very simple but exceedingly Practical Navigator U. Washington, DC,pp. Building such a mini-sextant to pro- Remember that the Sun is extremely duce a specific pattern of images bright, so only the reflected images involves sexrant geometrical optics, a should be observed, and these for good introduction to more ygvind only brief periods of time. Figure 4 is ed geometrical optical design involv.
Learn more about Scribd Membership Bestsellers. Read Free For 30 Days. Much more than documents. Discover everything Scribd has to offer, including books and audiobooks from major publishers. Start Free Trial Cancel anytime. Bris Sextant. Uploaded by kwayneolson How to build, calibrate and use to take sun shots.
Though he notes that the light sextant stars is too dim to use with the Bris, I wonder if making a "night" version with the welding shade replaced sextanh a piece of clear glass wouldn't allow for star and planet shots, too. Date uploaded Apr 05, Did you find this document useful? Is this content inappropriate? Report this Document. Flag for inappropriate content. Download Now. Related titles. Carousel Previous Carousel Next. Detection and Sizing Techniques of Connected Cracking.
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Swedish Boatbuilder Is Creating 'Survival Capsule'; Packing Books, Sardines
The Bris sextant /ˈbriːs/ is not a sextant proper, but is a small angle-measuring device that Sven Yrvind (Lundin) developed his Bris sextant as part of his quest for low-cost, low-technology equipment for ocean crossings. The Bris is a. Has anyone got a Sven Yrvind sextant that they would like to sell? The price of a new one is astronomical - Euros. Obviously he is trying to.
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