When choosing a swimming aid, many beginners wonder about the design of the bottom. balk Polyvinyl chloride (PVC) inflatable boats have a unique flexibility to create different bottom configurations, each of which solves specific tasks on the water.
The main function of this element is to improve hydrodynamics and course stability. Without an additional longitudinal rib, a lightweight inflatable boat, when exposed to wind or side wave, begins to prowl, requiring constant thrustering, which not only tires the operator, but also increases fuel consumption if used. boat-engine.
In this article, we will take a closer look at design features, compare bottom types, and find out where the keel is critical to safety and comfort, and understanding these nuances will help you make the right choice when buying or upgrading your vessel.
Principle of operation and hydrodynamics
The keel is the longitudinal protruding part of the bottom, running from the transom to the forehead. In water, it acts as a stabilizer, cutting the water flow and preventing the hull from lateral displacement. When the boat moves, the water flows around the keel, creating pressure that aligns the vessel relative to the direction of travel. gelling.
Without a keel, a flat-bottomed boat behaves like a sheet of plywood thrown into the water: it is constantly being tossed aside, the presence of a protruding element increases the sediment, but gives an invaluable (priceless) course-stabilityThis means that the boat becomes less susceptible to wind gusts and lateral current.
And the keel also acts as a powerful force element, and it takes on some of the load when it hits a wave, and it spreads the voltage throughout the structure, and this is especially true in inflatable models, where the stiffness is determined by air pressure and inserts.
⚠️ Warning: Installing a powerful motor on a flat-bottomed boat without a keel can lead to a dangerous yaw effect at high speeds, which is fraught with tipping over.
Inflatable keel: design features
One of the most popular solutions in the segment of budget and medium-sized boats is the inflatable keel, which is structurally a separate high-pressure chamber that is inserted into the hull or is an integral part of it. foot-pump Or a compressor.
The main advantage of this system is the ability to fold the boat into a compact backpack, an inflatable keel in a deflated state takes up almost no space and does not weigh the structure, but there are nuances: it must be carefully pumped to the state of a “ringing string”, otherwise it will not perform its function.
If the pressure in the keel balloon is insufficient, under load it will bend, and the boat will lose its driving qualities. PVC and TPU They're very durable, and they often use rubber or plastic overhead keels to protect them.
How to properly pump an inflatable keel?
Pump the keel last, after the main pressure is set in the cylinders, this will ensure maximum rigidity of the structure. Pressure should be about 0.2-0.25 atm (depending on the model), check with a pressure gauge.
Hard keel: aluminum profile and plywood
A more advanced solution is a rigid keel made of aluminum profiles or multi-layered plywood with plastic coatings, which are installed on boats designed for more serious operation and powerful engines, and a rigid profile provides ideal bottom geometry that does not change during operation.
Aluminum keels often have a complex shape, resembling an inverted letter "T" or a profile with faces. This allows you not only to keep the course, but also effectively divert the spray to the sides, improving visibility and reducing the splashing of the cockpit. SLIDE Or analogues.
The undeniable advantage of a hard keel is its durability, which is almost impossible to damage when in contact with sand, stones or mooring, but it requires more space for transportation and storage, because it will not be rolled into a tight roll — it will occupy a three-dimensional case.
When assembling a boat with a hard keel, always check the locks or fasteners. the Luft profile can cause creaks and damage to PVC tissue while driving.
Comparison of driving qualities: keel against flat bottom
The difference in behavior of boats with different types of bottom becomes apparent at medium speeds. If you plan to use the vessel for quiet fishing in quiet water, a flat bottom may be preferable because of less draught and stability in place. But for active walks and overcome the excitement of the keels are necessary.
Keel boats are easier to glid into planing mode, not slapping on the water, but plane confidently across the surface, which reduces the load on the transom and the engine, and also makes handling more predictable, with turns with less roll and radius.
Below is a table comparing the main specifications of different types of bottoms:
| Parameter | Flat bottom | Inflatable keel | Hard keel. |
|---|---|---|---|
| Course stability | Low. | Medium | High. |
| Compact assembly | High. | High. | Low. |
| Speed of exit to plane | Slowly. | Medium. | Fast. |
| Comfort on the wave | Low. | Medium. | Highly |
As you can see from the comparison, the choices are based on priorities, if mobility and weight are important, inflatable options are chosen, and if you want maximum performance and reliability, rigid profiles are preferred.
Impact on safety and manageability
Safety on the water depends on predictability of the vessel's behavior: a boat with a well-defined keel is less prone to sudden reversal across the wave, which is one of the common causes of small boats capsizing. When moving against a wave, the keel helps the boat "push" into the water and gently pass through the ridges rather than jumping on them.
And the driveability also benefits. When you're in the sharp maneuvers you need to get around obstacles or other boats, the boat responds to the rotating of the rompell or the helm instantly and clearly. The flat-bottomed counterparts have inertia and can continue on the old trajectory for several meters, which is unacceptable in an emergency.
This is particularly important when driving a boat with a powerful engine, and the center of gravity shifts, and without a keel, the boat can start to roll on board in a turn, and the keel acts as a counterweight and stabilizer, keeping the hull upright.
⚠️ Warning: Don't overload the boat with passengers and cargo. Overweight increases draft, and the keel's efficiency decreases, which can lead to a wave overflowing the board.
Keel care and protection against damage
The keel, especially the lower part, is in constant contact with the bottom, sand, rocks and snags, so the condition of this element requires regular inspection. Inflatable keels are often fitted with removable protective tapes made of dense rubber, which must be checked periodically for glue detachment.
Hard aluminum keels are susceptible to corrosion if not anodized alloy, or mechanical damage (dents). Plywood keels are afraid of moisture, so it's important to monitor the integrity of the plastic coating. If water penetrates the layer of plywood, it will swell and lose strength.
To extend the service life, it is recommended to wash the bottom with fresh water after each trip, especially if the swim was in salt water. It is better to keep the boat in straightened form or neatly rolled up, avoiding clamps in the area of the keel beam.
☑️ Checking the condition of the keel
Choosing a boat for specific tasks
So what exactly is the keel for? If your goal is to go fishing quietly on a small lake in windless weather, where maximum stability is important in place (so you don't stagger when catching fish), then a flat bottom or a very soft inflatable keel will be optimal. You can get up in a boat full-length without risking your balance.
However, if you plan to fish in Ladoga, Onega, the sea bays or just like speed and drive, the keel is a must. It will allow you to feel confident even when you are excited 1-2 points. For hiking trips, where every kilogram and liter of volume in the trunk counts, a high-pressure inflatable keel will become the golden mean.
Professional models for rescue services or the military are almost always equipped with a rigid allotment or a full-fledged rigid keel for guaranteed handling in all conditions. NDMA (low pressure inflatable floor) or NDVD (high pressure) where the keel is part of the structure.
The keel turns an inflatable boat from a simple boat into a full-fledged boat that can safely overcome the wave and develop high speed.
Frequently Asked Questions (FAQ)
Can I install a hard keel on a boat with an inflatable floor?
As a rule, the design of inflatable floor boats (BBB) does not provide for the installation of an additional rigid keel, since the geometry of cylinders and stringers is already designed for a certain shape. Modification is possible only within the framework of factory tuning, if the manufacturer provides such options (for example, the insertion of hard skis).
How much does the keel increase the weight of the boat?
An inflatable keel adds a minimum weight (about 0.5-1 kg depending on size) A hard aluminum or plywood keel can weigh a kit by 2-4 kg, which is essential for carrying in a backpack, but almost imperceptible when transported in a car.
Is it true that with a keel, the boat rows worse on oars?
Yes, it is. The keel increases the resistance of water when rowing. If you plan to use oars as your main engine often, having a pronounced keel can be uncomfortable, and in such cases, you choose to compromise with a soft, overhead keel, which you can lower a little.
How to repair a puncture in an inflatable keel?
Repairs are similar to repairs to the main boat: damage site detection, degreasing, PVC glue application and patching. It is important to use two-component polyurethane glue to ensure high-pressure tightness.