Influence of one screw on the controllability of a single-rotor ship. Factors Affecting Vessel Handling - Propeller Influence

The maneuverability of a propeller vessel largely depends on the number of propellers and their design. As a rule, the more screws a ship has, the better its maneuverability. By design, propellers can be different. On ships of the river fleet, mainly four-blade fixed-pitch propellers are installed, which, depending on the direction of rotation, are divided into propellers of the right (Fig. 25) and left-hand rotation (pitch). The right-hand propeller of a vessel going forward rotates clockwise, the left-hand propeller rotates counterclockwise when viewed from the stern to the bow of the vessel.

Rice. 25. Right hand propeller

The efficiency of a propeller largely depends on the conditions in which it operates, and above all on the degree of its immersion in water. The bare propeller or the excessive proximity of the propulsion-steering complex to the water surface significantly impairs the propulsion and controllability of the vessel, while the inertial characteristics significantly deviate from the nominal ones (the path length and acceleration time increase, the braking process deteriorates). Therefore, to ensure good maneuverability of propeller-driven ships, they should not be allowed to sail with a large trim on the bow or empty (without the necessary ballasting).

A working propeller makes two movements simultaneously:

moves translationally along the axis of the propeller shaft, giving the vessel translational motion forward or backward, and rotates around the same axis, shifting the stern in a lateral direction.

Consider the nature of the flow of water from a working propeller. If it works in forward motion, it forms a jet of water behind the stern of the vessel, twisted in the direction of its rotation and directed to the rudder blade (Fig. 26, a). The water pressure on the rudder blade in this case depends on the speed of the ship and the speed of the propeller: the higher the speed of the propeller, the stronger its effect on the rudder and, consequently, on the controllability of the vessel. When the vessel moves forward, a tail stream is formed behind its stern, directed in the direction of the movement of the vessel and at a certain angle to the stern of the hull, which also affects the controllability in a certain way.

When the propeller is running in reverse, the swirling jet of water is directed from the propeller towards the bow (Fig. 26, b) and exerts pressure not on the rudder blade, but on the hull of the aft part of the vessel, causing the stern to deviate in the direction of propeller rotation. However, the higher the frequency

propeller rotation, the stronger its effect on the lateral displacement of the ship's stern.

When the propeller is operating in forward or reverse motion, several forces are generated, the main of which are: the driving force, lateral forces on the propeller blades, the force of the jet thrown onto the rudder blade or body, the force of the associated or counter flow from the propeller, as well as the forces of water resistance vessel movement.

Controllability of single-rotor vessels. Consider the influence of the screw on the controllability of the vessel in forward motion (Fig. 27). Let us assume that a single-rotor ship with a right-handed propeller is drifting, having neither translational nor rotational motion, and the propeller is set to forward with the rudder straight. At the moment the propeller is turned on in forward motion, its blades begin to experience water resistance (the reaction forces of the propeller are hydrostatic), directed in the direction opposite to the rotation of the blades.

Due to the difference in water pressure along the immersion depth of the propeller, the hydrostatic force Da (Fig. 27, a) acting on blade III is greater than the force d] acting on blade I, which is closer to the water surface. The difference between the forces Da and di causes the stern to shift in the direction of the force Da, i.e. to the right. The hydrostatic forces Da and D4 are directed vertically in opposite directions and do not affect the ship in the horizontal plane. Despite the fact that the initial period, i.e., the moment the propeller is turned on, is very short in time, the navigator must take into account the phenomenon of stern yawing in the direction of propeller rotation.

After the screw develops

Rice. 27. Schemes of forces arising during the operation of the propeller in forward motion

a given frequency of rotation, in addition to hydrostatic forces, hydrodynamic forces of the jet thrown onto the rudder blade are formed (Fig. 27, b). The steady-state operation of the propeller in forward motion is characterized by the fact that blades I and III throw jets away from the rudder blade without exerting pressure on it, and blades II and IV throw a stream of water onto the rudder. In this case, the hydrodynamic force Pf is much greater than P due to the difference in water pressure along the depth of the blades II and IV, as well as due to air leakage at the upper position of the propeller blade.

With the steady rotation of the propeller, the action of the reaction forces of the water acting on the propeller blades and the jet thrown onto the rudder stabilizes, and behind the stern of the vessel a tail stream is formed with a force B, which is decomposed into components b\ and bh (Fig. 27, c) . The speed of the associated flow increases with the increase in the speed of the ship and reaches its maximum value at the steady speed of the full speed of the ship. In this case, the largest lateral component b\ of the passing force

The flow acts on the aft part of the ship's hull in the direction opposite to the rotation of the propeller (i.e., with a right-hand rotation propeller, to the left).

Thus, in a steady forward motion, a ship with a right-handed propeller is subject to the sum of three lateral forces: the hydrostatic force D (the reaction force of the water acting on the propeller blades), the hydrodynamic force P (the force of the jet thrown onto the rudder blade) and the lateral component associated flow forces bi, and (2P+Sbi)>SD.

As a result of this, the ship's stern deviates in the direction of the direction of the sum of the forces P and L \, i.e., with a right-hand screw, to the left, and with a left-hand screw, to the right. The deviation of the stern causes the ship's bow to deviate in the opposite direction, i.e., the ship tends to arbitrarily change course with a right-hand screw - to the right, and with a left-hand screw - to the left.

These phenomena must be taken into account in the practice of steering a single-rotor ship and remember that the agility of such ships in the forward course in the direction of rotation of the screw is much better than in the opposite direction. The circulation diameter of single-rotor ships with right-hand rotation of the screw to the right along the course is much smaller than to the left, and for ships with left-hand rotation of the screw, the opposite is true.

Let us consider the effect of a right-hand rotation screw during its operation in reverse. When the propeller is turned on in reverse, its blades experience the action of hydrostatic forces, the sum of which is directed to the left side, since Oz> 0[ (Fig. 28, a). Having developed speed, the screw creates a spiral flow of water directed under the hull and on the aft part of the hull, and does not affect the rudder. In this case, the hydrodynamic force P, acting-. pressure on the ship's hull from the jet thrown by the blade IV is greater than the hydrodynamic force Pg from the jet thrown by the blade II

(Fig. 28, b), due to the fact that the force P4 acts on the body almost perpendicularly, and the force P-r - at a slight angle to the body. As a result of this, the ship's stern deviates in the direction of propeller rotation.

When moving in reverse, there is no passing flow and the vessel is subject to only the sum of two groups of lateral forces: the reaction forces of water and the forces of throwing a jet onto the hull, directed in one direction, as well as the forces of the oncoming flow. In this regard, the work of the propeller in reverse has a strong influence on controllability, due to which individual vessels in reverse become uncontrollable.

In the practice of navigation, it is necessary to take into account that when working in reverse, single-rotor vessels with a first-rotation propeller throw the stern towards the port side, and with a left-hand rotation propeller - towards the starboard side, and the propeller turning moment is usually greater than the rudder turning moment.

In order to avoid loss of ship controllability, it is recommended not to set a high propeller speed in reverse and, if necessary, switch it to forward with a short-term increase in speed.

The fact that with a twin-engine installation it is desirable to have propellers of the opposite direction of rotation is well known to all motorists (the question of the influence of the direction of rotation of propellers on speed and controllability has been considered more than once on the pages of "KiYa"). It is known that athletes in races sometimes turn on one of the two motors with the same direction of rotation of the propeller in reverse and thanks to this they get an increase in speed of several kilometers per hour, and most importantly, they achieve better stability on the course (naturally, this motor requires replace the propeller so that it produces forward thrust when astern).

Long-term work, for example, "Whirlwind", in reverse gear is undesirable, since the design of the propeller shaft supports is not designed for the constant perception of the propeller stop in reverse gear. Therefore, sometimes different types of motors are installed on motorboats: in addition to the Whirlwind or Neptune (with the right rotation of the propeller), they put Hi-22 - the only domestic motor that has a left propeller.

Having made a few simple parts, it is possible to adapt the Whirlwind gearbox to work with a left-handed propeller: this will make it possible to use the same type of outboard motors with a twin-engine installation, which is advisable from the point of view of ease of operation and repair.

In the design of the left-hand rotation gearbox I made, I had to abandon the reverse gear: to ensure maneuverability, it is enough to have a reverse gear on one of the two motors, and each engine has an idle gear.

To install the bearings, it is necessary to make a new glass 3 (it is best to make it from stainless steel). With the help of a round file or an emery stone, a hole is cut on the side surface of the glass for the passage of the reverse thrust.

Sleeve 4 is machined from bronze. Four grooves 1.5 wide and 1 mm deep are sawn through its entire length along the inner hole with a hacksaw to lubricate the bearings and gear 5. The sealing of the gearbox housing on the screw side is ensured by installing two seals 1. The reverse gear 5 must be machined on a mandrel with a diameter of 30 ± 0 .02 mm with a surface finish of 7-8 class.

The forward gear 7 must be modified according to the dimensions indicated on the sketch. I recommend choosing for this purpose a gear already in operation with teeth worn on one side and clutch protrusions. Ring 6 is pressed into the groove of the gear with a diameter of 38 mm, which serves to reduce the travel of the clutch 10.

When assembling the propeller shaft assembly, cuffs 1 are first pressed into glass 3, then ball bearings 7000103 lubricated with grease and (with a tight fit) bronze bushing 4 are installed. , and the cams of the clutch 11 were engaged with the cams of the gear 5. The gap in the engagement of the gears is adjusted using the rings installed between the gear and the end face of the glass 3.

I have been using the “Vikhr-M” with a redesigned gearbox for the fourth year on the “Kazaik-2M” and I use a propeller from the “Privet-22” engine (diameter 235 and pitch 285 mm) on it. I didn’t specifically measure the speed of the boat, but I’ll say that on the Volga in Cheboksary my “Kazanka” is the fastest among boats with two outboard motors.

After two seasons of operation, I had to change the ball bearings 7000103, which, constantly taking the propeller stop, received a large output. Perhaps it makes sense to use angular contact bearings.

Helical surface control.

Bent on impact, for example, on the bottom, the propeller blades must be straightened immediately, otherwise the operation of the propeller will be accompanied by strong vibration transmitted to the hull of the boat, and its speed may be significantly reduced.

To test the blade, make pitch squares like the one shown in the figure. rice. 222(pitch must be known or previously measured on a serviceable blade).

Pitch squares are cut out (first in the form of templates from tin or cardboard) for four to six screw radii r , equal, for example, to 20, 40, 60 and 80% of the largest radius R.

The base of each pattern must be 2 l r , i.e. 6.28 of a given radius, and the height is a step N.

On a flat board, arcs are drawn with the corresponding radii and a propeller is installed in the center with the injection surface down. By bending the cut out square along an arc of the appropriate radiusr ,bring him under the blade.

Having marked the width of the blade and the position of its axis on the template, cut off unnecessary parts at the ends of the template and transfer the markup to a sheet of metal 1-1.5 mm thick. This will be the test step square, which, of course, should also be bent exactly along the arc of a controlled radius.r .

The screw should be installed on the board in such a way that it can be rotated (fig. 223). A snug fit of the injection surface across the entire width of the blade to the step angle will indicate its correct shape.

Pedometer square.

You can quickly and accurately determine the pitch of the screw using a pedometer square (Fig. 224), made of transparent plexiglass. Each slanted line on the ruler corresponds to the pitch of the propeller at a certain radius (for example, 90 mm) of the blade. Screw pitch in centimeters (Fig. 224, a) indicated at the end of the slanted lines. Slanted lines should be clearly visible. They are drawn with a sharp tool and pointed with black paint.

They use a square as follows: from the center of the screw axis on a flat - pumping surface of the blade, lay a radius equal to the base of the square (in our case, 90 mm), and draw a line perpendicular to the radius. The square is placed on the drawn line and look through it at the cut of the hub. The pitch of the screw will be determined by that inclined line that will be parallel to the cut of the hub (in our example H≈ 400 mm).

The principle of constructing a square is clear from rice. 224, b. A radius of 90 mm is plotted horizontally, and various propeller pitch values ​​divided by 2l are plotted vertically. You can choose a different radius, according to the size of the screw.

Right or left?

Depending on the direction of rotation of the propeller shaft, when viewed from the stern, right (clockwise) and left rotation screws are used. Two simple rules will help you distinguish between them.

1. Place the propeller on a table and look at the end of the blade facing you. If the right edge of the blade is higher - the right rotation propeller (Fig. 225, b), if higher left - left (Fig. 225, a) . In this case, you will make sure that it does not matter how the screw lies: the front (nose) or the rear end of the hub on the table.

2, Put the propeller on the ground and try to put your foot on its blade without lifting the heel from the ground. If at the same time the sole of the right foot fits snugly on the surface of the blade, your propeller is right-handed, if left-handed, then left-handed.

With the same propeller, is it possible to achieve maximum speed and maximum load capacity?
No. To achieve high speed, a pitch or diameter that is not suitable for the load capacity is used - where operating conditions are completely different. If you want to get by with one screw, then decide what is most important based on that and choose the screw.

3 or 4 blades?
For most boats, 3-blade propellers are recommended. These propellers provide good acceleration and main speed operation.
A three-bladed propeller has less drag and allows (theoretically) more speed. The four-bladed one has a larger emphasis, the speed with this propeller in modes from low speed to 2/3 should be higher.
4-blade propellers are recommended for heavier boats and boats with high performance hulls equipped with more powerful engines. Compared to 3 blades, they work better during acceleration and have less vibration at high speeds.

For my boat there is a 13" and 14" propeller. A smaller diameter with a larger pitch - is it the same?
Pitch cannot replace diameter. The diameter is directly related to the motor power, RPM, and speed that your requirements indicate. If the operating conditions require a 13" diameter, then installing 12" will reduce its effectiveness.

Is it necessary to use heat to install or remove a screw?
Heat should never be used when installing a screw, and therefore, should rarely be required for removal. If it is not possible to remove the screw using a soft hammer, gentle heating with a blowtorch may help. Do not use a welding torch as the fast, sharp heat will change the structure of the bronze, creating internal stresses that could cause the hub to split.

What is the benefit of using a second screw - left hand rotation?
Two propellers working in the same direction on boats (vessels) will create a reactive moment. In other words, the two right propellers will tilt the boat to the left.
Two counter-rotating propellers on identical motors will eliminate this reaction torque because the left propeller will balance the right propeller. This will result in better straight line motion and high speed control.

Aluminum or stainless steel?
Most boats are equipped with aluminum propellers. Aluminum screws are relatively inexpensive, easy to repair, and under normal conditions can last for many years.
Stainless steel is more expensive, but much stronger and more durable than aluminum.

Why are different propellers used with motors of the same power?
This is due to differences in the reduction ratios of the engine. The motor is designed so that the propeller shaft turns more slowly than the crankshaft. This is usually expressed as a ratio, such as 12:21 or 14:28. In the first example, the crankshaft ratio would be 12 and the propeller shaft gear would be 21. This means that the propeller shaft would only turn 57% of the RPM into the crankshaft. The lower the gear ratio, the larger the pitch of the screw, and vice versa can be used.

Screw torque compensation.
The steering wheel (steering wheel) must be located relative to the rotation of the propeller. If the engine has a right-hand rotation of the screw, the rudder (steering wheel) should be on the right or on the starboard side. This bead usually tends to rise as a result of the reaction torque, and the driver's weight compensates for this.

What is the role of the rubber shock absorber in the screw hub?
It is not intended to protect the blade from impact, as is sometimes believed. This device protects the gears of the gearbox, softening the impact on the screw. Its main purpose is to prevent excessive wear or breakage of the engine gearbox gears that can occur due to the impact that occurs during the shifting process.

The rubber buffer in my prop seems to be slipping. Is it possible?
Such a possibility exists in principle, but it does not happen very often. Inspect the propeller, if the blades are visibly bent or distorted, then you are probably experiencing cavitation - cavitation is often perceived as sleeve sliding. The bushing can be replaced if needed, or the blades can be rebuilt to the proper accuracy to eliminate cavitation.

cavitation- this is the phenomenon of the formation in the liquid of small and almost empty cavities (caverns), which expand to large sizes, and then quickly collapse, producing a sharp noise. Cavitation occurs in pumps, propellers, impellers (hydroturbines) and in the vascular tissues of plants. When the caverns are destroyed, a lot of energy is released, which can cause major damage. Cavitation can destroy almost any substance. The consequences caused by the destruction of cavities lead to a large wear of the components and can significantly reduce the life of the propeller.
Cavitation, (not to be confused with ventilation), is water "boiling" due to an extreme reduction in pressure at the tip of a propeller blade. Many propellers partially cavitate during normal operation, but excessive cavitation can cause physical damage to the propeller blade surface due to microscopic bubbles bursting onto the blade. There can be numerous causes of cavitation, such as mismatched screw shape, improper installation, physical damage to the cutting edge, etc...

Regarding the plastic screws.
No screws to date have had better properties than screws made from metals. A good screw should have a long service life and be repairable. While available plastics lose in all these parameters.

Is it possible to get by with one standard screw, which is equipped with a motor (boat)?
A specially selected propeller will work with greater efficiency than the standard universal propeller that comes with the boat. It is optimal to have at least two screws, and even better three, from which you can always choose the one you need for various boat loads.

§ 46. Factors affecting manageability.

1. Influence of the propeller.

The control of the vessel largely depends not only on the rudder, but also on the design of the propeller, its speed of rotation and the contours of the stern of the vessel.

Propellers are made of cast iron, steel and bronze. The best propellers for boats should be considered bronze propellers, as they are light, well polished and resistant to corrosion in water. Screws are characterized by diameter, pitch and efficiency.

The diameter of the propeller is the diameter of the circle described by the extreme points of the blades.

The pitch of the screw is the distance along the axis of the screw that any point of the screw moves in one complete revolution.

Rice. 103. Formation of threads of screws

The efficiency (efficiency d) of the propeller is determined by the ratio of the power developed by the propeller to the power expended on its rotation.

The operation of the propeller is based on the hydrodynamic force created by rarefaction on one and pressure on the other surface of the blade.

Modern ship propellers are still very imperfect. Thus, propellers, on average, spend about half of the power given to them by the engine uselessly, for example, on the helical twisting of water particles in a jet.

On boats, two-, three- and less often four-bladed propellers are used. On fishing boats, propellers with rotary blades or the so-called propellers with adjustable pitch are sometimes installed, which allow you to smoothly change the speed or direction of the vessel with a constant one-way rotation of the propeller shaft. This eliminates the need to reverse the engine.

Screws differ in the direction of their rotation. A propeller that rotates clockwise (if you look at it from stern to bow) is called a right-handed propeller, counterclockwise - left-handed. When moving forward under the aft gap of the ship-pa hull, a passing water flow (Fig. 103) is formed in front of and behind the rudder and forces arise that act on the rudder and affect the agility of the vessel. The speed of the associated flow is greater, the fuller and dumber the contours of the stern.

The vacuum on the convex side of the blade, called the suction side, sucks water towards the propeller, and the pressure on the flat side, called the discharge side, pushes the water away from the propeller. The speed of the ejected jet is approximately twice that of the suction. The reaction of the ejected water is perceived by the blades, which transmit it to the ship through the hub and the propeller shaft. This force that sets the ship in motion is called thrust.

In a stream of water thrown by a screw, the particles do not move in a straight line, but in a helical fashion. A passing stream, as it were, stretches behind the vessel and its magnitude depends on the shape of the stern of the vessel. The flow somewhat changes the pressure on the rudder retracted from the center plane of the vessel.

The cumulative effect of all flows has a noticeable effect on the ship's controllability; it depends on the position of the rudder, the magnitude and change in speed, the shape of the hull, the design and mode of operation of the propeller. Therefore, each vessel has its own individual features of the action of the propeller on the rudder, which the navigator must carefully study in practice (Table 4).

Table 4

The influence of the interaction of the propeller of the right rotation of the rudder on the behavior of the vessel.

The screw of left rotation, under equal other conditions, will give the opposite results given in the table.

If the ship has a right-handed propeller, the ship will turn better to the right, the circulation diameter to the right will be smaller than to the left.

In reverse, the agility of the vessel is usually worse. A ship with a right-handed propeller in reverse is better turned stern to port than to starboard. Therefore, on a ship with a right-hand pitch propeller, they tend to approach the berth on the port side, as in this case, with a change of course to the rear, the stern will be pressed against the wall.

On some motor yachts and boats, two motors are installed, each with its own shaft and propeller. In this case, the screws usually rotate in different directions. They can be installed either with outward rotation, i.e., in the upper part, the blades go from the middle to the side, or with inward rotation, when the blades in the upper part go from the side to the middle. This or that direction of rotation of the screws, as well as the inclination of the axes of the screws and shafts to the horizontal and diametrical planes, are of great importance in terms of agility.