Operating a soft-floored inflatable vessel often becomes a test of endurance, especially when riding a wave or going against the wind. Lack of a hard support under the feet causes the leg muscles to work constantly, keeping balance, which quickly leads to fatigue. That is why the question of how to book the bottom of a PVC boat becomes relevant for most owners of budget models and low-pressure inflatable floor vessels (LND).
The modernization process, which is called “reservation” in the boating environment, involves installing hard sheet material on top of the regular inflatable floor, which can be moisture-resistant plywood, composite panels or sheet aluminum, which radically changes the performance of the boat, turning it from an unstable “duck” into a full-fledged glister with predictable behavior on the water.
However, when you decide to do this, it is important to understand that you increase the overall weight of the vessel and change its center of gravity. Incorrectly selected weight of armor can lead to a critical transom overload or reduce payload to a minimum. In this article, we will discuss in detail all the steps of turning a soft bottom into a hard floor, calculate the optimal thickness of materials and discuss the nuances of installing inflatable stringers.
⚠️ Attention: Hard bottom installation significantly increases the total weight of the boat. Be sure to check the product passport before starting work and make sure that the total weight of passengers, engine, fuel and new armor does not exceed the maximum permissible carrying capacity specified by the manufacturer.
Selection of material for hard decking: plywood, aluminum or composite
The first and most important step is to choose the material that will form the basis of your armor. The market offers several options, each with its own advantages and disadvantages, most often the choice is between laminated plywood and aluminum-magnesium alloy.
Laminated plywood The most popular choice is due to the availability and ease of processing. FC (moisture-resistant) or FSF (increased moisture resistance), necessarily covered with a phenolic film on both sides, the thickness of the sheet usually varies from 6 to 9 mm, which provides a balance between rigidity and weight.
An alternative to the tree is aluminum-leaf or composite panels based on aluminum mesh. AMG (aluminum-magnesium) is non-rust, highly durable and lasts for decades, but it's harder to cut at home, and it can be noisier when waves hit the bottom.
- 🌲 Plywood: It is easy to process, cheap, but over time it can be layered with constant contact with water and requires high-quality sealing of the edges.
- ⚙️ Aluminum: eternal material, does not absorb moisture, light, but expensive and requires a special tool for cutting.
- 🛡️ Composite: combines the strength of the metal and lightness, often has an anti-slip coating, but is more expensive than analogues.
When choosing the thickness of the material should take into account the power of the engine. For boats for an outboard motor up to 5 hp, 6 mm plywood is enough. If you plan to put the engine 9.9-15 hp, it is better not to save and take 9 mm or use an aluminum sheet 3-4 mm thick. The critical parameter is the weight of one square meter of material: for plywood it is about 7-8 kg, for aluminum - about 2.7 kg.
Open and prepare the elements of the bottom
After purchasing materials, you need to make a precise cut. A mistake in size even 1-2 centimeters can cause the sheets to not fit into the slots or, conversely, will hang around, creating dangerous backlashes. The ideal solution is to create a cardboard pattern that repeats the geometry of the bottom of your particular model of boat.
If you use plywood, the ends of the sheets after cutting must be carefully grinded and covered with several layers of epoxy resin or special yacht varnish, this will prevent moisture from entering the layers of the veneer, which inevitably leads to swelling and destruction of the sheet. Aluminum edges are also desirable to treat, so that sharp edges do not damage the cylinders when stacked.
A standard PVC boat typically consists of three or four sections of the bottom, and when cut, it is important to provide technological gaps between the sections, which are necessary so that when balloons and stringers are inflated, the material does not rest against each other, creating unnecessary stress, but has the opportunity for natural expansion.
| Type of boat (example length) | Number of sections | Recommended thickness (plywood) | Recommended thickness (aluminum) |
|---|---|---|---|
| 2.80 - 3.00 m | 3 sections | 6-7 mm | 2-3 mm |
| 3.20 - 3.50 m | 3-4 sections | 7-9 mm | 3 mm |
| 3.60 - 4.00 m | 4 sections | 9-12 mm | 3-4 mm |
| 4.00+m (flat bottom) | 4-5 sections | 12 mm + profile | 4-5 mm + profile |
To connect sections with each other at a professional level, aluminum profiles or special connecting tapes are often used. However, for a budget option, it will be enough to simply tightly dock the treated edges, which will later be slammed with inflatable stringers.
Installation of inflatable stringers: the basis of rigidity of the design
The key to the hard bottom system is inflatable stringers, long cylindrical cylinders that are placed along the sides in special pockets or slots, and it is the pressure in the stringers that creates the "spreading" effect, pressing the bottom sheets against the sides and giving the entire structure a monolithic appearance.
The installation process begins with the laying of hard bottom sections inside the boat, the sheets are placed on the normal soft bottom (or directly on the shell if the soft bottom is removed, although this is rare), it is important to monitor the symmetry: the central axis of the bottom should coincide with the diametric plane of the boat.
Then, stringers are inserted into the side pockets between the sides and the hard deck, and when they are pumped, the magic of transformation occurs: the soft structure becomes hard as concrete, the pressure in the stringers should be high, usually about 0.25-0.3 atmosphere (or according to the instructions for specific stringers).
Use a pressure pump to pump stringers. Eye pumping often results in an uneven distribution of pressure, which can cause the bottom to wave or, conversely, not to break up to the end.
There are boat models where stringers are part of the design and models where you need to buy them separately. When buying, make sure that the diameter of the stringers matches the slots of your boat. Too thin a stringer will not create the necessary tension, and too thick can simply not fit into the designated pocket or tear fabric when overblown.
Trans part reinforcement and slag installation
The transom area is under maximum stress, especially when planing. The wave hits the stern, and if it's just a sheet of plywood, cracks or squeezing over time, so booking often involves installing an extra sleigh (protective mat) or strengthening the transom plate.
If your boat's regular bottom is made of PVC fabric, it makes sense to put a layer of dense linoleum or special reinforced fabric under hard sheets, which is a layer that will protect the inner surface of the cylinders from rubbing against the rough surface of plywood or aluminum under dynamic loads.
For hinged transom boats (HTD), it is important that the hard bottom reaches the very end, providing uniform support. In some cases, owners glue a wooden bar or profile to the back edge of the last sheet of the bottom, which serves as a thrust and prevents the bottom from moving forward.
⚠️ Warning: Never use corrosion-prone materials (steel, unpainted iron) to reinforce the bottom, and when exposed to high humidity and water, they will rust in one season, damaging the boat's fabric and losing strength.
Also worth paying attention to is the condition of the valves. When installing a hard bottom, access to some valves can be difficult, check their performance before the structure is fully assembled, so that you do not have to blow the boat away because of the air-infecting valve under the plywood.
Construction and initial testing
Building a booked boat requires a sequence of actions that is different from pumping a conventional inflater, first the boat is folded and slightly blown to spread the folds, then the sections of the hard bottom are laid.
After you put the sheets in, you start pumping the stringers, and you do this evenly, blow a little bit to the left, then blow to the right, controlling the tension, and if you pump one side, the bottom can get arced, and the final step is to get the pressure in the main cylinders to the working value.
☑️ Checklist of correct assembly
The first test is best done in shallow water or in a calm zone near the shore. Pay attention to the behavior of the boat: whether there is an uncharacteristic roll, not "cruising" underfoot. The hard bottom should feel like a single platform. If you press the foot section of the bottom bends down, then the pressure in the stringers is not enough or the thickness of the material is chosen incorrectly.
An important aspect is drying after use: hard bottom, especially plywood, must be removed from the boat and dried separately. Left in assembled form for a long time, plywood can be banned, and water caught between the layers will turn into ice in the winter and damage the structure of the material.
Operational nuances and care for hard bottom
Operating a boat with a reserved bottom imposes its obligations on the owner, primarily in terms of storage. If a conventional PVC boat can be kept rolled up all year round, then the plywood boat is better kept spread out, or at least not wet the plywood before packing.
The aluminum bottom is less demanding, but it needs to be maintained, and sand and small pebbles between the metal and the PVC fabric work like an abrasive, so always clean the interiors carefully before packaging.
Can I paint the plywood bottom?
Yes, you can and should. Two-component epoxy paints for yachts or special rubber paints (like Rubber Paint) are the best for this, creating an elastic coating that does not crack when deformed and perfectly protects the tree from water.
Check the edges of the sheets regularly. If you notice that the lacquer coating on the plywood has begun to crack, immediately restore it. Moisture is the main enemy of multi-layered materials. For aluminum, check the cutting sites for burrs that may have appeared during operation.
A properly selected and installed hard bottom prolongs the life of the boat, distributing the load over a large area and protecting the soft bottom from punctures and grinding.
Frequently Asked Questions (FAQ)
How much will the weight of the boat increase after the installation of armor?
For a boat 3.20-3.50 m long, the weight of the plywood bottom (3-4 sheets) will be from 15 to 25 kg depending on the thickness. The aluminum counterpart will be lighter by about 40-50%, that is, it will add about 8-12 kg to the total weight of the kit.
Can I use conventional construction plywood?
Structural plywood (FB grades or regular birch without impregnation) will quickly absorb moisture, swell and lose strength. Use only moisture-resistant plywood of FC or FSF grades with laminated surfaces.
Do I need to clean the bottom before installation?
Using talc or silicone lubrication between layers (boat fabric and hard bottom) makes assembly and disassembly easier, and also reduces friction. However, beware, the lubrication should not be aggressive to the PVC material (avoid solvents).
Will the boat sink if water is in the hard bottom?
The hard bottom itself is not a floating element, it only gives shape. If water is collected, it will be at the bottom. Plywood can absorb some of the moisture, which will add weight, but will not cause instant flooding if the cylinders are intact. However, the presence of water under the feet on the glister is dangerous loss of stability.