Installation of longitudinal redans on motor boats. Planing vessels
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It is known that on the gliding gliding motor boats and boats with a deadrise of the bottom 10 ° and higher, large masses of water are thrown from the keel to the sides, which leads to significant friction losses and wave formation. Splashes generated by the movement of such boats, poured the deck and fall into the cockpit.
One of the effective ways to reduce wave formation and use the energy of spray jets is to install longitudinal overlays on the bottom, or redanshaving a special profile. Redanyconvert the flow energy into additional lift and, as a result, reduce the wetted surface of the bottom. The schematic diagram of the location of the redans is shown in rice 88.
Fig. 88
Longitudinal redany.
a - the layout of the redans on the width of the boat; b - wetted bottom surface without redans; in - the same with redans.
1 - bottom surface not wetted with water; 2 - malar splash breaker; 3 - longitudinal redan; 4 - transverse water flow; 5 - wetted part of the bottom.
Motor boatwith longitudinal redan creates a much smaller wave in the transitional mode, and when leaving for gliding, the nasal wave in some cases disappears altogether, the stern wave decreases significantly and takes the form of a spray jet. This is due to the fact that the flow of water, breaking out from under the keel and directed at a certain angle to the side, meets in its path a profiled step-redan and breaks off from the bottom of it. Jets of water explode at a smaller angle to the horizon, and the wetted surface decreases. As a result, increase the speed and efficiency of the vessel.
Besides redansincrease the stability of the vessel, reduce the side and longitudinal pitching. On the move, with a sharp heel on the redan, an additional lift force arises, which prevents a further increase in roll.
The experience of operating vessels with longitudinal redans shows that the indispensable condition for the correct operation of redans is strict observance of their parallelism to the keel, starting from the middle part of the hull and further into the stern. An error of a few degrees or, especially, a zigzag shape (in plan) of the redan may lead to an increase in resistance. The same can happen in the case of the use of redans, which in their dimensions do not correspond to this body. In the nose part it is better to reduce them a little to the stem in order to avoid lifting too steep upwards. Otherwise, when you shoot on the nose wave, the redans will increase resistance.
On hulls with flat-keeled contours should be put redans of triangular section with a horizontal bottom edge, the width of which is usually taken within 1 / 30-1 / 40 width of the bottom of the boat. It is desirable that the transition from the bottom surface to the working face of the redan is smooth, and the free edge of the corner is sharp.
Close to optimal sizes of the cross-section of the redans for the bottom with a deadrise of 20-23 ° are shown in fig. 88. With a lower deadrise, the height of the redans should be increased, and with a deadrise less than 10 °, it is impractical to use them.
Their number and size depends on the dimensions of the hull and the speed that this vessel is capable of developing. Redans of the same type, but with a slightly smaller wall height A ( rice 89 ).
Fig. 89 Installation of redans on the case with a flat-keeled bottom (option with two redans on the side).
The work of redans improves in all cases, if a small visor is installed along the edge of flow B, as shown in rice 90.
Fig. 90. Recommended sections of redans: a - with a plate-visor; b - with a slope of the wall.
Since in some cases it is difficult to get the required profile with a visor or to install a visor from a separate strip, it is advisable to make wall A with a small blockage.
For most hulls, the most successful results are redans, located at a distance from the keel, approximately equal to half a half-width or a little more. If there are several redans, they are more often placed closer to the cheekbone.
On a flat-bottomed and convexly keeled body, the external wing should be installed as close as possible to the cheekbone.
Longitudinal redans along the entire length of the hull - from the stem to the transom are used only on high-speed boats with a speed exceeding 40 km / h. At lower speeds, the lift generated by the redans will not compensate for the increase in resistance due to an increase in the wetted surface. In this case, it should be limited to installing short redans only in the zone of intensive spatter formation in the nose of the bottom.
The articles by G. S. Malinovsky on the longitudinal redans of the editors received many letters from readers, especially from the owners of the “kazanok”, with a variety of questions. They are interested in the details of the installation of redans: their length, location along the length and width of the boat, dimensions, cross-section profile. And one fan of high speeds from Irkutsk asked if he would not get an extra 5 km / hour by attaching the redans to his “Trickle”? !!
Here we will have to immediately disappoint the owners of flat-bottomed gliding boats: longitudinal redans on such vessels will not give much effect. Recall that the effect of the longitudinal redans consists of cutting off water from the bottom of the boat and creating additional lifting force, which reduces the draft of the hull, and therefore reduces the wetted surface and friction resistance. At the same time, this part of the water flow under the bottom that “works” on the redans, which spreads in the transverse direction, to the sides, and falls on the redans at an angle close to the straight line. And such a flow is the more intense, the greater the deadrise of the bottom. That is why it was precisely on boats with a bottom grip of 15–20 ° that redans first appeared.
On flat-bottomed boats, such as the Kazanka, the cross-flow is small, and the usual long redans, instead of benefit, will be harmful, since they only increase the wetted surface. It is enough to put such boats in the bow, at the border of the running waterline, to fix a couple of short (500-600 mm) splash breakers.
If the boat has a monoghedron-type bottom with a constant and sufficiently large (7-13 °) deadrise from the mid-section to the transom, it is recommended to install two redans. One of them should be located closer to the cheekbone and stretch it to the transom, the second - in the front third of the length of the bottom of the boat. Putting a larger number of redans, as it is done on seaworthy to because keeled racing boats, does not make sense. The fact that such vessels are completely covered with redans, including the boards, is explained by the need to effectively cut off the water from the skin when the hull enters the wave. Redans on such boats often extend from the stem to the transom. since the position and area of the “working area” are constantly changing during the course of the agitation - the boat then completely jumps out of the water and spends some time on the propeller, it falls on the water with the whole board.
By the way, for seaworthy boats it is very important and the property of the redans to reduce the swing of the side and pitching pitches. With a sharp roll on board, additional lifting force arises on the side of a leaning side and provides great resistance to further roll.
Another important sign (besides kplsvatostp bottoms), speaking g, the benefit of installing redans, is the high speed of the boat. The boat must really glide so that the bottom sections in the nose and near the cheekbones, where the redans are located, come out of the water. On such a displacement and low-speed boat, like the “Trickle”, the redans will not be wound across, but along and, naturally, no lifting force on them can arise. Moreover, the lift on the redane is proportional to the square of the speed of the boat. Therefore, we can conclude that for four-, five-meter boats, long redans are advisable to pour at a speed of 40-50 km / h.
How to properly arrange redans - on buttocks or waterlines? When swimming in calm water, it does not matter, as part of the redans in the nose is located above the water. But if the bottom is in contact with the wave, the picture will change dramatically.
If the redans are oriented along buttocks, they rise steeply in the nose, so the wave hits the working plane of the redan at a large angle and the ship's motion slows down, which is accompanied by water dropping upwards, to the sides, and even forward. Energy is wasted on the useless rise of these splashes, passengers wallow in this waterfall. Therefore, such an arrangement of longitudinal redans, taken on the first hunt boats, was subsequently abandoned and now they are located parallel to the waterline. Moreover, on the last designs of boats, redans are applied with different angles of inclination to the waterline so that their working planes are directed at the most advantageous angle to the incoming flow of water under various conditions. The first to the keel of the redan is usually parallel to it, and the redans at the cheekbones and on the sides have a slight inclination to the plane of the waterline. But this difference is very small. It should be remembered that when planing, the optimum angles of attack of the bottom, and hence the redans to the incident flow, are within 4-6 °. These values are critical and must be maintained when installing redans.
At a speed of 60 km / h and more, the pressure of the water on the drawers reaches 4 kg / cm 2, so even a small error in the angle of their installation leads to a significant loss of lift and reduces the possible increase in speed.
The cross section of the redans is a triangle with a smooth transition in the bottom and, if possible, with a sharp free (working) edge. The bottom, working edge of the redana should be horizontal; its width is from 35 mm on motor-boats with a length of 4 m with a speed of 30-40 km / h to 70-80 mm on boats with a length of 6 m and a speed of over 50 km / h.
The latest innovations are characterized by the location of the redans, adopted, for example, on the French six-seater plastic boat "Siap". The main data of this boat: length 5.50 m; width 2.20 m; board height 0.99 m; light weight - 785 kg. With two Crescent installations (column at 45 °) with a capacity of 55 liters each. with. the boat has a maximum speed of 51 km / h, with a single installation capacity of 155 liters. with. - 69.4 km / h.
The bottom of the boat has molded bilge dampers and three longitudinal openings on board. In the picture you can see that the two nearest to the keel redan extend only part of the length of the boat, ending at the probable border of the bottom of the wetted surface. The angle of the external deadrise of the bottom on the transom is 30 °, the radane width is about 80 mm. You can see that redans are located almost on the waterlines and only slightly rise at the stem.
Another positive effect from the longitudinal redans has been revealed - they significantly increase the boat's stability on the course and at the same time reduce the circulation radius. The ego is due to the work of the lateral, vertical faces of the redans, which, when laterally shifting the hull (drift) when turning, away from wind, waves, etc., act similarly to a falshkil. In order to increase stability on the course, it is possible to recommend the installation of redans on flat-bottomed boats, i.e., where the speed increase is almost not given.
In conclusion, we note that the cross wrap scheme of the longitudinal drag, considered in issue 11, is somewhat simplified. In fact, the flow of water here is directed not in a single plane, but in space. The dimensions of the cross section of the redan are small, it is located in close proximity to the hull of the vessel, where the laws of viscosity and boundary layer apply. Therefore, the study of the effect of redans on the driving performance of a ship and the choice of their optimal sizes on scale models is extremely difficult: tests often give conflicting results. Fully the effect of redans can be found only on a full-scale vessel. Therefore, it is advisable, given the lack of reliable data for designing redans, to perform them in the form of bottom plates that can be easily removed, moved or replaced.
The editors of the collection will be grateful to all lovers who reported the basic data of the redans they used on their boats and the results obtained. This will be systematized and will allow the development of more specific recommendations on the installation of longitudinal flow rails.
The following note by Nizhny Novgorod water motor Yu. M. Petrov, in our opinion, will be useful to many owners of high-speed boats. The author does not just suggest a theme for creativity, but recommends a real and relatively inexpensive way to increase the speed of the motor boat.
Of course, it is very good that powerful imported motors appeared at the price of a Zhiguli car. Someone can buy - frolic, but most of these fans remain with their old "twenty" and "thirty". I would like to help such amateur enthusiasts in terms of improving propulsion, reducing yaw, increasing seaworthiness, increasing speed, and also reducing fuel consumption in the presence of small capacities.
I started installing redans in 1970 in order to improve the hydrodynamic qualities of my simplified “sledge” (for boats with this type of contour, see the pages:
For the test, two elementary (40 mm wide) zygomatic redan-splash pads were installed, which cut off the water, improved the gliding and increased speed. Later, when finalizing the bottom of the sled, two more powerful zygomatic redans were installed (80 mm wide at the transom), one each on the external zygomatic surfaces and four redans in the mine in the forward part of the hull.
Approximate scheme of installation of bottom longitudinal redans and zygomatic splash breakers
A - simplified "sea sleigh"; B - plywood version of the PK-5 motor boat;
B - serial Progress-2; G - round-hulled boat with the engine "GAZ-21";
D - three-hued Fox Sea Sleigh.
Two redan with a length of 1.5 m was installed on the side surfaces of the bottom. This allowed us to improve seaworthiness, reduce yawning, and thanks to the rise of the bow and reduce the wetted surface of the bottom: the speed of the boat increased. Redans were made of pine and each was placed on 4 screws with sealant.
The zygomatic redans (120 mm wide), installed from the stem to the transom along the waterline on a 7-meter round-bore Gorodets-built boat, allowed her to go gliding (water cannon from GAZ-21). Before the installation of redans, with increasing engine speed, a meter-high water shaft rose before the nose of the boat and the speed did not increase.
When fine-tuning my Fox Sea Sledge, I installed 80 mm redans on the side surfaces of the central ski and redans of the original form on the side-mounted splash guard (which practically did not work). On the bottom, the redans began to work at a speed of 10 km / h. With increasing speed, the water, without washing the mine, went to the transom. There was a decrease in the wetted surface of the bottom, the course on the wave became softer. Airborne redans were made by analogy with the Flipper 909 boat, but with a slight improvement. Redan plates with a length of 500 mm were made of sheet metal and superimposed on the bottom of the splash guard on the waterline with an overlap of 20 mm and fastened with 4 M4 screws. Redans were bent along a radius of 40 mm, and ended in a straight shelf 5-8 mm wide, parallel to the PD. The effect of the shelf was amazing, the water went to the transom, twisting and falling off the side without splashing. The engine then developed only 3000 revolutions per minute (ignition advance was not regulated due to significant wear of the camshaft gears), however, I achieved a speed of 39 km / h due to good performance of the redans. I note that when installing the longitudinal redans, the trim at the stern is increased. This is useful if there is a bottom fold down at the transom. If there is no limb, the installation of a transom plate is required.
1 - mounting bracket, steel δ = 1; 2 — plate, steel δ = 3, size “a” along the flange width; 3 - pickaxes for mounting adjustment lanyards.
I hung an adjustable plate directly on the jet, securing it to the holes between the flange of the water intake and the nozzle flange. Later, two underwater wings were installed behind the transom at the bottom level.
Installation of stern hydrofoils behind the transom of my Fox Sea Sleigh
Possessing a large lift, these wings made it possible to have a significant feed load. However, when changing the load requires additional adjustment of the angle of lift of the wings. Ideally, if such adjustment could be made from the driver's seat.
All experiments were carried out in the presence on the instrument panel: a pressure gauge (up to 1 atm.) With a flip-down sensor on the bottom and a tachometer.
I think that in order to fully utilize the engine power and obtain high performance, it is necessary to install effective redans on all types of motor boats and even some yachts (on the waterline to reduce the wetted surface of the board and reduce the roll). I am surprised by the designers of new motor boats and boats that do not understand this. Even on the new “Master” motor boat, the available redans do not work with full dedication. The picture shows that with a sufficiently powerful motor, the board is excessively washed out.
I would like some firm to start producing modern radius of several standard sizes for self-installation by suicide lovers on their boats. I give an approximate profile redana.
1.5-2.0 mm thick (light alloy)
The radius can be set by increasing the width of the redan. The number and length of the redans are best chosen empirically, according to the recommendations of the magazine. The main thing is that the redans overlap each other. Installing two redans on the bottom and two cheekbones redans, as a rule, gives positive results. Profile redan can be extruded or extruded from aluminum alloy.
The motor boat began to walk gently along the wave, the wetted surface in the mine decreased. There was no water shaft in the bow of the mine at the time of going to gliding, and the time of exit was reduced. At the speed, we heard the characteristic rustle from the good work of the redans. All working planes of the redans were installed with an angle of 15 ° from the DP down to the bottom.
According to my advice, the longitudinal redans were placed on a flat-bottomed plywood variant of the PK-5 motor boat. Her yawing capacity decreased, her germination improved on the wave, which made it possible to establish the driver and passenger seats in the bow. Redanov was found: four on the bottom and two on the cheekbone (only 30 mm wide).
In conclusion, it remains to wish amateur navigators: do not regret the time to install and manufacture redans. Your work pays off by increasing speed, improving seaworthiness and reducing fuel consumption.
Yu. Petrov, Nizhny Novgorod, “Boats and Yachts”, 1998
The hydrodynamic effect of longitudinal redans manifests itself in several directions. First, the redans cut off the water from the bottom of the boat, reducing its wetted surface. Secondly, additional lift is created on them, which, together with the first factor, contributes to improving the quality of the hull. Thirdly, using longitudinal redans, it is possible to obtain an optimal gliding bottom width and a specific load coefficient C B.
The positive properties of the longitudinal redans begin to manifest themselves only at sufficiently high speeds - with Fr D\u003e 4. At low speed (or when the boat accelerates) water resistance due to an increased wetted bottom surface with redans is higher than that of a boat with a smooth bottom.
The efficiency of redans depends on whether the bottom of the water sections located to the side of the redan touch the edges of the water reflected by their edges. This is due to the steepness of the side walls of the wave depression, which is formed by planing a flat or keel plate. At the lateral edges of the flat plate, where the rate of transverse spreading of water is small, these walls are almost vertical - water rises sharply under the action of a pressure drop across the cheekbones. At the edges of the keel plate, the velocity of transverse flows is high, so the jets are pulled out here at an angle to the vertical (Fig. 1), and, the greater the keel angle of the bottom, the greater the deviation from the vertical. With a deadrise value of about 20 °, the angle of inclination of the walls of the depression is almost equal to this value.
Fig. 1. Wave cushion roll walls at the hull with increased dead water. The right shows the action of the longitudinal redana.
Close to optimal sizes of the cross-section of the redans for the bottom with a deadrise of 20-23 ° are shown in fig. 2, with less deadrise, the height of redans is recommended to be increased; when the deadrise is less than 10 ° to use them impractical. 
Fig. 2. Longitudinal redans: a - layout of redans across the width of the boat; b - view of the bottom of the boat without redans; in the action of redans on the same bottom.
1 - bottom surfaces not wetted with water;
2 - malar splash breaker;
3 - longitudinal redan;
4 — transverse water flow;
5 - wetted part of the bottom.
Longitudinal redans along the entire length of the hull - from the stem to the transom should be used, if only you can count on gliding of the hull at a given width. Otherwise, the redans in the aft bottom only increase the water resistance. Usually, only the extreme ones are brought to the transom to the cheekbone, and the rest, which work effectively in the area of the bottom meeting with water at full speed, are cut off at a certain distance from the transom. On motorboats having a low deadrise of the bottom and a speed of less than 40 km / h, it is possible to install short (0.5–0.8 m) reddish splash-breakers in the area of intensive formation of splashes - the nose of the hull.
Redans should have a close to triangular cross section with a horizontal bottom edge. It is desirable that the transition from the bottom surface to the working face of the redan is smooth, and the free edge of the corner is sharp. On wooden boats, redans are often made of hardwood or attached to their working edges metal strips.
In the middle part of the hull and aft, the redans are arranged parallel to the keel. In the nose part it is better to reduce them slightly to the stem (in plan) in order to avoid lifting too steeply upwards (on the side); otherwise, when the body shoots on the wave, the redans have an inhibiting effect.
For each half of the bottom, it is usually installed in two (with a boat width of 1.4-1.6 m) or three (with a width of 2-2.5 m) redan. The position of the extreme cheekbones is determined by calculation depending on the speed and load of the boat.
Longitudinal redans increase the stability of the boat, moderate side and longitudinal pitching. In the course of a sharp roll, additional lifting force arising on the sides of the leaned side prevents a further increase in roll. Another positive effect: longitudinal redans significantly increase the stability of the boat on the course and at the same time reduce the radius of circulation. This is due to the work of the side vertical edges of the redans, which, when laterally shifting the hull (drift) when turning from the wind or wave, act like a keel.
At the same time, longitudinal redans give a negative effect on high-speed boats when sailing on a wave. With the oncoming wave, the hull receives hard blows due to the concentration of pressure on the flat surfaces of the redans.