Every boat owner, whether it's a compact PVC inflatable model or a solid aluminum boat, sooner or later faces the question of hydrodynamics: Why does one boat jump easily to planing at minimal engine power, and another, seemingly similar in size, stubbornly "growls" nose and refuses to go into mode? The answer lies in the geometry of the bottom, namely, in elements called redans.
Understanding the principle of operation of these design features allows not only to competently choose a vessel for specific tasks, but also to properly operate it. redane It's not just a decorative element or a stiff edge, it's a complex engineering system that controls the flow of water and air, and ignoring their use can lead to increased fuel consumption, discomfort during the course, and even reduced safety on the water.
In this article, we will explore in detail the physics of the process, the types of structures and the practical aspects of operation, you will learn how the shape of the bottom affects the behavior of the vessel at different speeds and why knowing these nuances is critical for the skipper.
Physics of the process: how does redane work
First, we need to determine, What is a boat rental? It's a ledge, or a sharp fracture, of the bottom surface, that is used to divert water and splash from the sides, and to create an air cushion, and when a boat moves, the water flows around the hull, and without special guides, it would create a tremendous friction force that would brake the boat.
When the boat is speeding up, the flow of water under the bottom meets this ledge, and at that moment, the flow breaks off, and air is sucked under the flat part of the bottom between the redans or from the side to the redane. cavernAnd that's why the boat is lifted up above the water, not just on the bottom, but on the redans and the transom plate, which is called planing.
⚠️ Warning: Attempting to get on plane on a boat with damaged or deformed redans can lead to a sharp loss of controllability and "travelling" the vessel from side to side.
Thus, the main function of the element is to reduce water resistance and improve germination on the wave. Hydrodynamic properties The right angle or shape can cause the boat to be constantly splashed or, conversely, "goat" at high speed.
The main types of rents and their purpose
Boat designers use different shapes of protrusions depending on the operating conditions for which the vessel is intended, and there are several main types, each with its own advantages and disadvantages.
The first type is longitudinal redeemerThey run all the way from the transom to the forehead, and their main task is to stabilize the course, and they work like keels to prevent lateral slip (drift) and yaw, and boats with pronounced longitudinal redanes are more confident in their course at the lateral wave.
Type two: transom They're located across the symmetry axis and they create a sharp ledge, and they're the ones that most effectively pull the nasal part off the water, providing a quick exit to plane. PVC and aluminum, a combined scheme is used.
And we also have what's called splash-back redans in the bow, which deflect the flow of water down and to the sides, preventing it from spilling over the side, which is critical to keeping passengers and equipment dry in the nose cockpit.
Redeemed on PVC boats against aluminum hulls
The material of the hull dictates its limitations and possibilities in the molding of hydrodynamic elements. reinforced polyvinyl chloride The redans are formed by the design of inflatable tubes and rigid paiole (or low-pressure inflatable floor), in which the redans are often performed by the cylinders themselves, if they have the appropriate cross-sectional shape.
In aluminum boats, the situation is different: reds are squeezed or welded as separate elements; metal allows for more complex and sharp edges, which theoretically gives a better effect of water separation; however, sharp aluminum edges are more susceptible to impacts on underwater obstacles than elastic cylinders. PVC.
Inflatable boats often rely on keelIt's a brilliant engineering solution that allows you to transport a boat in a deflated state, and on the water you get the specifications close to a rigid hull, and it's important to monitor the pressure in these keels, because their insufficient rigidity will reduce the efficiency of the redane to zero.
Impact of workload on redans
When the boat is fully loaded (passengers, cargo, fuel), the draught increases, in which case the geometry of water entering the redeemed zone changes, the boat may need more time and engine power to go into the plane, as the area of contact with water increases, and the air cushion is more difficult to form.
So when choosing between PVC and metal, it's not just weight and transportability that you consider, but also how the material holds the shape of the redane under load. The hard case is more stable, but the soft one forgives errors when mooring and impacting.
The influence of the bottom shape on planing and speed
The shape of the bottom and the location of the redans directly determine how quickly the vessel will enter the planing mode. Flat bottom with minimal redans allows you to go early to planing even at low power, but this is comfortable only in quiet water.
A silky bottom with deep rentans It's better at cutting the wave, making it smoother. But it takes more power to go out there, and the air under the bottom is more difficult to suck, and the nose stays submerged longer.
The critical parameter is the angle of keeliness, and the bigger it is, the better the boat is at the excitement, but the higher the engine requirements, and the redans in this scheme act as stabilizers, keeping the boat from burrowing or tilting too much.
☑️ Checking readiness for glossing
Owners should remember that there is no such thing as a middle ground, and one configuration is suitable for fishing on a calm lake, and a completely different configuration for sea trips. The optimal form of red is always a compromise between early planing and comfort on excitement.
Problems of operation: cavitation and yaw
Improperly designed or damaged reds can cause serious problems, one of which is cavitation, and although the term is more commonly referred to as a propeller, in the context of the bottom, it's about chaotic water separation, and if the flow breaks off in the wrong place, the body vibrates.
The second problem is yaw, if you're left and right. longitudinal redeemerIf you are not in the boat (for example, one is lowered and the other is inflated, or there is a deformation of metal), the boat will constantly be led aside.
There is also the "dolphining" effect, where the boat starts to peck rhythmically in the water and up at full speed, often due to improper alignment or improper operation of the nose redans, which can not keep their nose in the desired position.
| Type of problem | The probable cause is in the redans | Effects of consequences |
|---|---|---|
| Difficult exit to plane | Underfloor pollution, lack of air cushion | Fuel overconsumption, engine overheating |
| Strong spraying | Damage to nose spray-cutting redans | Getting water into the cockpit, getting things wet |
| Searching the course | Asymmetry of lateral redanes | Fatigue of the driver, risk of loss of control |
| Hard hits against the wave | Flat bottom without pronounced keel redanes | Discomfort, risk of damage to equipment |
Tuning and finishing the bottom DIY
Many enthusiasts are looking to improve their boats' performance by refining the bottom. Aluminum boats sometimes weld additional profiles or cheeks onto the transom to change the angle of water outflow, but such interventions require a deep knowledge of hydrodynamics.
Boat owners. PVC They often experiment with adding extra inflatables or reconfiguring the floorboard, for example, a more rigid plywood floorboard with profiled redanes can significantly improve the plane, but it's important to remember that any change in bottom geometry changes the center of gravity and buoyancy.
⚠️ Attention: Independent welding of metal profiles to the bottom can violate factory corrosion protection and lead to rapid rotting of the body in the welding sites.
If you're not sure about your engineering skills, you should just clean the bottom of the seaweed and the seashells on a regular basis, and a smooth surface is the key to efficient operation of regular redans, and any growths disrupt laminar flow and negate the efforts of designers.
Use silicone sprays to treat the bottom before launching, which will reduce fouling and facilitate slipping, increasing the efficiency of the redan.
Maintenance and maintenance of the bottom elements
And lease They've been doing their job for years, and they need to be taken care of, and after every run into the water, especially in salt water or overgrown water, the bottom needs to be washed, and the salt and organics that are left over break down the material and create roughness.
When transporting a boat on a trailer or roof of a car, special linings should be used, they should repeat the contours of the hull, so as not to deform the area of the redans, constant pressure at one point can lead to irreversible deformation, especially on PVC.
Regularly inspect the surface for cracks, chips or scuffs. In aluminum boats, the impact sites of stones can become hotbeds of corrosion. In PVC, even a small cut in the bending zone of redan during pumping can cause the cylinder to rupture.
The state of the bottom surface is more important than it seems: even microscopic roughness creates turbulence that dampens speed and increases fuel consumption.
Can you increase the speed of the boat by changing the shape of the redan?
Theoretically, yes, but in practice, it's difficult: changing geometry (for example, mounting a hydrofoil on a transom or sub-gluing profiles) can give an increase of 5-10%, but requires accurate calculations.
Why is an inflatable floor boat (BBB) doing better than a floorboard boat?
Low-pressure inflatable floor (LDPB) when pumped creates a more pronounced and smooth profile of keeliness and redanes than typed plywood, and the absence of joints between the paiola sheets improves streamlining.
Does the color of the bottom affect the work of redans?
No, color doesn't affect hydrodynamics. But the light bottom is less heated in the sun, which is important for PVC materials. The dark bottom can mask the fish boat, but it burns out and warms up faster.
What if the boat is constantly moving away at full speed?
Check the engine installation (vertical), the condition of the lower unit and the symmetry of the boat loading. If all is well, it may be damaged one of the on-board redans or the cylinder has a deformation.
Do I need to lubricate the redans before launching into the water?
No special lubrication is required, but cleanliness is required, and the use of antifouling coatings for the bottoms of the boat is permissible and prolongs the period between cleanings, keeping the surface smooth.