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PERSONAL TRANSPORT: GROUND, WATER, AIR
Trimarans Strizh. Personal transport
Directory / Personal transport: land, water, air The conversation will be about a new type of sailboat - a light, affordable and versatile trimaran vessel, the basis of which is a collapsible tourist kayak with a soft shell. Such trimarans have many advantages, and one of the important ones is the low cost of the kayak itself and additional sailing equipment. In addition, such a vessel does not require a stationary parking on the shore - a mezzanine in the apartment is enough; You can deliver a trimaran to a reservoir even by public transport, not to mention the train. Well, if you also get a good tent, in terms of comfort, traveling in a trimaran will not differ much from relaxing in a floating cottage. It is worth noting that the speed of the trimaran reaches 15 km/h, which is commensurate with the capabilities of yachts, and the safety of navigation is higher than on a light dinghy. The latter is essential if you prefer a holiday on the water with your family.
We will introduce you to several simple trimarans of the "Strizh" type, which were developed specifically for those who were going to become the owner of a sailing vessel for the first time. Each trimaran from the "Swifts" family has only one sail - the mainsail, that is, it also applies to ships with cat-type weapons. Its mast is supported by a stay and two shrouds, each of which is bifurcated at the bottom and attached to two transverse beams of the bridge, which makes it possible to evenly distribute loads between them. The beams lie on the bulwarks of the kayak; on the front there is a step - the heel of the mast rests on it. At the ends of the beams, inflatable floats with a volume of 20-100 liters are installed in oilcloth fairings reinforced with stringers. The design scheme of the trimaran made it possible to completely abandon the strengthening or alterations of the hull of the kayak, to significantly simplify and lighten the bridge. The "softness" of the entire structure and the sharp bow formations of the central hull and floats allow the vessel to overcome even half a meter waves. But no more - in case of strong waves, it is better not to move away from the coast, since waves more than half a meter high can flood the central building.
The sails of the "Swifts" have an unusual shape. First of all, there is no traditional boom with all its shortcomings, and the luff has actually turned into a second rear one. Cables are passed through the leech and leech pockets, which allows you to adjust the mast bend in accordance with the shape of the sail and the strength of the wind. All of this combined makes our sail more efficient than a traditional Bermuda mainsail. A set of simple tricks, with the help of which its shape is rigidly set, which is automatically saved when changing operating modes, allows even beginners to sew a quite decent sail. Of course, subject to the methodology of cutting and sewing and constant "fitting" on the spars. These are, in general terms, the design features of trimarans of the Strizh family. Strizh-4 The attractiveness of this trimaran lies in the low weight of additional equipment (only 8-9 kg) plus the relative ease of construction. The 4m2 sail accessory can be used on many kayaks, but best results are obtained when fitted to light Hummingbird type kayaks. For the bridge of the trimaran, you will need two duralumin oars (from the Salyut kayak) attached to the bulwarks. The front paddle beam, on which the mast will be installed, is located at the very beginning of the cockpit, and the rear one - at a distance of 1050 mm from the front one. The blades of the oars are turned upside down so that in motion with a roll they slide on the surface of the water (planing), thereby reducing the roll. The angle of their installation is 5-10°, it is provided by a special fastening of the stringers of the floats to them. For floats, you will need covers made of oilcloth and "baby logs for playing on the water" (as they are called in stores for children). The capacity of each is about 20 liters. The "log" is inserted into the case and pumped up through the valve led into the hole at the end. Sew a long pocket for the float stringer to the cover. A sailor in a strong wind has to tilt the sailboat. To do this, he is located on board, leaning his hand on the pipe-handrail, fixed on the beams of the bridge. The heeling technique is to make the oars slide over the crests of the waves, and not plow the water with them. If the sailor does not have the opportunity to respond to every change in wind strength (for example, during long transitions), it is better to fix the floats under the blades of the oars. We offer you a choice of two sail options. The first is the simplest, it can be made from any Bermuda grotto of sufficient area. Cut off the lower triangular panel from it, insert an eyelet into the newly formed straight clew to attach the boom leg. The position of the heel of the boom on the mast is chosen such that the boom would have a horizontal position during the normal roll of the trimaran. From the tack and phage angles to the grommet of the clew, cables of future luffs are pulled. Steel cables Ø 1,5-2 mm are best suited for this purpose. It is possible, of course, to use vegetable or synthetic ropes, but due to their uncontrolled shrinkage or stretching, constant adjustment of the actual length of the ropes will be required.
If the sail being finalized had armor and a "sickle", then you will have to get rid of them - this will greatly simplify further work. After that, tuck the fabric along all three luffs, achieving the correct shape of the sail over its entire area. This means that the smooth bulge ("belly") of the sail should reach a maximum in its geometric center and be 5-8% of each of the horizontal sections. In fact, the largest "belly" is formed in the boom area, since this section works in the most advantageous mode, then the bulge gradually decreases and has a minimum value in the upper part of the sail, which somewhat reduces the heeling moment. Some loss of area of the modified sail compared to the original Bermuda also reduces the roll moment and, accordingly, the drift, but on sharp courses the sail thrust can even increase, since the remaining part of the fabric has an optimal angle of attack to the wind regardless of height, the correct "belly" at all plots; as well as a smooth surface without folds and wrinkles. The second option is somewhat tricky. It consists of "two panels stitched along all three luffs (the corners are not sewn together!). The masts and the boom are located inside. This sail design is an implementation of the idea of a wide automatically rotating aerodynamic mast. The mast (pipe) becomes a voluminous toe of the sail and, thus, does not adversely affect its performance. When setting and setting up this mover, the boom leg is passed between the clew corners of the panels and attached to it, and the boom heel has the ability to rise and fall along the mast from the tack angle to a position in which the boom is perpendicular to the mast. In a fresh wind, when the speed of the trimaran is high, the bridge starts to work with an overload. In this case, the boom is gradually raised up the mast. In this case, the distance between the mast and the clew increases, but since the length of the luffs is constant, this causes the mast with the boom to bend up to 200 mm. Almost all the excess material "leaves" into the formed front sickle, creating a "belly" for the sail. When the boom is in the upper position, the pair is completely flat and strongly stretched, which corresponds to its minimum thrust and minimum drag. This technique of reducing sail thrust is more effective than the traditional "reefing". Corrugation can reduce the area of the sail by 1,5-2 times, respectively, the thrust will decrease, and the aerodynamic quality will deteriorate. By adjusting the "pocket" value, the coefficient changes from 1,2-1,5 to 0,2-0,3, that is, it decreases by 5-6 times. It is also important that the sail acquires the ability to work without rinsing at low angles of attack. This design has been extensively tested with the Salyut-4 and Neptune kayaks and, according to numerous reviews, is the most suitable for both beginners and experienced sailing tourists. You can sew a sail from a light, durable, windproof material. Good results are obtained when using cushion teak. Some elasticity of the fabric is by no means a disadvantage, since it is easily compensated by adjusting the sail. It is best to make a mast from a duralumin pipe with an outer Ø 40 mm and a wall thickness of 1,5-2 mm. A good mast is made from a high jump pole. Strizh-4,5 The main advantage of this trimaran is its reliability, as it is designed for short and long distance tourism. With a moderate weight of additional equipment (13-16 kg), the sailboat has a good course not in all courses, high reliability, comfort, and ease of operation. The bridge of this trimaran must withstand significant loads, so it is best to make it from duralumin pipes (T40X1,5 or T40x2). The length of each beam is 2,3-3,6 m. The floats of this trimaran are displacement, their volume is from 35 to 50 liters each. Fairings with smoothly narrowed fore and aft parts are sewn from ordinary table oilcloth with a polymer layer on the outside and reinforced from above by two stringers each. The sail is attached to the mast using a pocket 250-300 mm wide, which acts as an aerodynamic mast. The boom is made double, it resembles a sailboard (windsurfer) wishbone. On the legs of the booms, several holes were drilled - each pair for swimming in a wind of a certain strength. Fixing the clew of the sail to the boom with an M6 bolt and a wing nut.
The "belly" of the sail is 5-10% of its width, it is set even before the sail is raised by selecting the appropriate holes on the legs of the boom and is corrected on the go by adjusting the tension of the luff cable. The fabric of the sail must first of all be strong and non-stretchy. Otherwise, the "belly" spontaneously increases with gusts and decreases with the weakening of the wind. Most suitable canvas weighing up to 350 g / m2; applicable filter cloth, tent, lavsan. Keep in mind that sewing a sail from a heavy fabric is easier, and besides, it is more durable. The mast of the Strizh-4,5 should be stronger than that of the Strizh-4. For it, you will need a duralumin pipe T50X2 mm. The rigidity of the product can be increased by installing spreaders with rhomboids. Of course, the additional standing rigging increases the assembly and adjustment time of weapons, but allows you to make a mast from available materials. Strizh-7 Distinctive features of this sailboat are its high speed and low weight. Already with a wind of 4-5 points, the traction of the sail reaches 35 kgf, which exceeds the traction of the outboard motor "Surf" with a power of 5 liters. With. A kayak (best of all, "Salyut-5,2"), deployed stern forward, with this sail develops a speed of over 10 km / h. Naturally, you have to pay for the speed with the weight of additional equipment (about 25 kg), a long setup and assembly time. In addition, the nodes of the sailboat must have increased reliability. Strizh-7 is best built if you have experience with simpler modifications of trimarans (Strizh-4, Strizh-4,5). The heeling moment on this trimaran reaches significant values, and the sailor's heeling work is no longer effective. You have to rely only on the restoring moment created by the floats and the total strength of the entire structure. For the bridge beams in this version, you will need a 150x2 mm dural tube. The volume of floats is about 100 liters. To do this, three "logs" with a volume of 40 liters are sequentially laid in each of the fairings. The valve of the middle "log" is closed tightly, and it is pumped through a new one, glued on the cylindrical surface with Vinix glue. A hole is cut in the fairing for it. This trimaran can also be sailed with fifty-litre floats, but it should be taken into account that even in medium wind they burrow deep into the water. Please note: if the float systematically enters the water by more than half, it is necessary to immediately reduce the thrust, reducing the angle of attack of the sail and its "belly".
For a trimaran, any of the sails described above will do. The anchor point of the shrouds is 1700 mm below the top of the mast. 5 Recently, the following method of tensioning canvas has begun to gain popularity: the tack and head angle are fixed, and the clew eyelet is attracted to the legs of the booms with a soft lanyard. This allows you to quickly reconfigure the sail, reduces the time for its installation and disarmament. On "Swift-7" the shvertsbalka is located at a distance of 400-450 mm from the mast. Centering is chosen forward to facilitate tacking. At the same time, the steering wheel is loaded slightly, since it is sufficiently removed from the center of lateral resistance. The screws to improve the hydrodynamic quality are made voluminous, with an asymmetric profile. Please note that, as a rule, there is always one shverts, located on the leeward side with a convex side to the kayak. Each of the screws is assembled from two duralumin sheets with a pipe or board placed between them that defines the profile. You can bend the screws from a single sheet or even plan from a board. The last option, by the way, gives the best results. It is only necessary to protect the wood with epoxy resin or parquet varnish from water and polish it to a glossy surface. The relative thickness of the shverts is 10%. Its profile can be simplified: one side is flat, the other is formed by arcs of a circle. Sharp edges on the screw should be rounded off. Tests have shown that in the entire range of operating speeds and angles of attack, the screws have a laminar flow around them. Separate filaments of the disrupted flow were caused by small burrs that were not noticed during the preliminary examination of the samples. Schwerts of other configurations did not give such a flow. It has been experimentally established that the initial angle of attack of the Shaers should not be more than 5 °, otherwise, due to their high hydrodynamic quality, the Schwertz carries the trimaran skidding into the wind, and the speed drops sharply. In conclusion, it should be noted that the three Swifts do not exhaust all the possibilities of a kayak trimaran. Amateurs are constantly experimenting, seeking greater strength from light and unpretentious sailboats, increasing the aerodynamic quality of the sail, making it easier to control it in gusty winds and heavy seas. Bridges of other designs are being developed, although the power scheme of the Swifts - two identical beams and bifurcated shrouds - will apparently remain the most acceptable for coastal navigation. Author: V.Peregudov
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