Legendary Ob 3M Although it is a very old base design, this boat, originally designed as a versatile means for fishing and recreation in small water bodies, is transformed in skilled hands into a reliable boat, able to confidently keep the wave and carry a powerful motor. Unlike its predecessors, the third version has received a number of design improvements aimed at improving stability and comfort, making it an ideal candidate for deep modernization.
The main feature of the model is its aluminumIt's made of an AMg5M alloy that's highly corrosion-resistant and tough, but the factory design is often criticized for being too noisy and spartan on board, which has led owners to take on the challenge of customizing things from the tiller console to the full interior skin, and has been keeping interest in the project for years.
In this article, we will discuss in detail the technical nuances, consider the real possibilities for increasing engine power and discuss time-tested methods of improving driving performance. Ob 3M It is often called a “constructor for adults” and how to turn a standard “iron” into a comfortable floating craft.
Technical specifications and design features
The basic parameters of the boat determine its potential and limitations. The hull is 4.5 meters long and the width on the midsection is 1.6 meters, which, with its own weight of about 150 kg (without equipment), allows you to carry up to four people or 400 kg of payload. An important parameter is the carrying capacity, which in the factory passport is limited, but in practice the hull withstands significantly more if you distribute the weight correctly.
The hull has squid-bottom The boat's track is designed to be powered by outboard motors up to 30 hp, although enthusiasts often put more powerful units in place to reinforce the design.
⚠️ Note: Operation of a boat with an engine above 30 hp requires mandatory reinforcement of the transom with additional scarves and bulkheads, since the standard aluminum may not withstand vibration loads and lead to the destruction of the aft part.
The table below shows the main comparative specifications of the standard and the full-load version:
| Parameter | Meaning | Note |
|---|---|---|
| Longest length | 4,500 mm | No trinkets. |
| largest width | 1600 mm | Midel-spangout. |
| Height of board | 700 mm | Midle. |
| Hull mass | 145-155 kg | Depends on the year of issue. |
| Passenger capacity | 4 people. | Including the cargo |
The longitudinal and cross-linking systems are well-designed for their time, but often require testing for fatigue cracks, especially in the mounting areas of cans and zygomatic stringers. Aluminum alloyAlthough strong, sensitive to spot impacts on rocks or ice, so the condition of the bottom should be monitored regularly.
Covering and insulation: turning cold metal into comfort
The most common modification that owners start with is cabin-plateIn the summer, bare metal turns into a pan, and in the fall and spring, it emits a piercing cold, and the noise level from the waves and the engine in the unsheathed boat makes communication almost impossible, and the most common way to solve these problems is using plywood (FSF or moisture-resistant FC) 4-6 mm thick in combination with insulation.
The process of skinning begins with a thorough cleaning of the inner surfaces of dirt and oxides, between the sides and bulkheads, a frame of bars or aluminum profile is installed, in the cells of which it is tightly fit. heaterAs the latter, it has proven to be foil-coated polyethylene foam or extruded polystyrene foam, which do not absorb moisture and do not rot.
Calculation of the quantity of materials
For a full 3M paneling, you will need approximately 8-10 sheets of plywood (size 1.5x1.5 m) 4 mm thick and 3-4 rolls of insulation. Don't forget to buy a special adhesive for metal and wood that is resistant to water.
Plywood sheets are mounted on top of the insulation, and it's important not to press them too tightly against the sides to keep the air layer that works as thermal insulation, and the attachment is done on pressed screws, the caps of which must be covered with plastic caps or sealed to prevent contact of the metal of the fastener with moisture.
- 🛠️ Tools: Drill, screwdriver, jigsaw, roulette.
- 🪵 Materials: Plywood FSF 4-6 mm, timber 20x30 mm, insulation.
- 🧴 Chemistry: Contact glue, silicone sealant, antiseptic for wood.
- 📏 In addition: Aluminum corner for edging plywood slices.
The final step is to paint the plywood with varnish or paint with marine paint, which not only improves aesthetics, but also creates an additional barrier to moisture. Some craftsmen go on to sheath the plywood with dermatine or special boat carpets, which finally turns the cabin into a comfortable cabin.
Upgrade of driving performance and installation of the engine
Staff Ob 3M It's designed for engines up to 30 hp, which allows you to reach speeds of about 35-40 km / h with full load, but many owners are looking to increase this figure by installing engines with a capacity of 40 or even 50 hp. This modernization requires a comprehensive approach: simply outweighing the engine is not enough.
The first thing you need to do when installing a powerful motor is transprancingThe standard stove may not withstand the increased strains of cutting and torsion. Usually weld or rivet additional scarves from the same alloy AMG5, increasing the thickness of the metal packet in the area of the lower unit niche, it is also recommended to check the condition of the zygomatic stringers, since at high speeds the load on them increases many times.
The second important aspect is the installation hydrofoil This simple device, mounted on an anti-cavitation stove, greatly improves the boat's planing output, reduces yaw on the course, and saves up to 10 to 15 percent of fuel. With its fairly full stern, this is a must-have tuning element for the Ob.
And we also need to keep in mind the weight distribution, because if you put a heavy four-stroke engine at 40-50 forces, the center of gravity shifts to the transom, and to compensate for that, you can move the battery and the fuel tank to the bow, placing them under the front seats or in a special john, which will improve the running differentiation and reduce the risk of being overwhelmed by the wave.
Tuning of interior and navigation equipment
The comfort of the water is made up of small things. Once the skin is solved, it's ergonomics. The regular wooden cans (seats) are uncomfortable for long transitions, so they are often replaced with soft chairs on swivel bases or make stationary sofas with runduks inside.
The organization of space under the seats is a great opportunity to place navigational equipmentIt is important to provide easy access to these areas without having to disassemble the entire cabin. For electronics (echo sounder, navigator, radio) a console or shelf is installed in the range of sight of the steering wheel.
- ⚓ Anchor system: Installation of the roller on the forehead and an anchor-cat weighing 4-5 kg.
- 💡 Lighting: LED tapes under banks and running lights that comply with the rules.
- 🔋 Electric: Laying of separate wiring for the motor and consumers with fuses.
- 🪜 Safety: Fastenings for life jackets and scoop.
The lighting issue deserves special attention. The boat is not equipped with electricity, so everything has to be done from scratch. Using LED tapes with IP67 moisture protection allows you to create a soft light that does not blind your eyes in the dark, and illuminate the handdukes to find gear.
⚠️ Attention: All electrical wiring in the boat should be done with copper wire in double insulation, all connections - securely shrink and covered with varnish or silicone.
Aluminum housing care and corrosion protection
Although aluminum It doesn't rust like steel, it's susceptible to oxidation and electrochemical corrosion, especially in salt water or in contact with heterogeneous metals. The basic rule of care is to keep the boat clean and dry. After each loading, especially if it was in salt water, the hull should be rinsed with fresh water.
Many owners use special paints to protect the bottom from abrasive wear and fouling, but with aluminum, you need to be careful: conventional copper-based antifouling paints are strictly prohibited, as they will cause rapid corrosion of the body. You need to use only specialized formulations marked "for aluminum".
If you keep the boat on the water for a long time, be sure to install zinc treads on a transom or cheekbones, which will take over the electrochemical corrosion, protecting the main body, and they will just need to be changed periodically.
Regular inspection of seams and riveted joints helps to identify the first signs of fatigue of the metal or leakage. If you notice white plaque (oxidation) in the riveting sites, this is a signal that the connection requires attention, cleaning and coating with special soil will prevent the development of the problem.
Drawings and schemes for self-redesign
For those who have decided to make a change Ob 3M The fact that you have accurate drawings is critical. You can find many variations on the Internet, but it's best to use factory diagrams to make adjustments to your needs. Basic lines, theoretical drawings and brangouts allow you to calculate the amount of material accurately.
When designing a skin or installing new bulkheads, it is important to observe symmetry with respect to the diametric plane (DP). Any shift in the center of gravity or change in contours can adversely affect the running performance. If you plan to install a control console, make sure that the gas and reverse cables pass in advance so that they do not rub or interfere with the legs.
☑️ Plan for the reworking Ob 3M
Keep in mind that any design changes, especially those related to increased passenger capacity or engine power, theoretically require re-registration with the GIMS. In practice, inspectors rarely require drawings for boats less than 5 meters long, but you need to know your rights and obligations as a boat owner.
The key to a successful Ob 3M redesign is not to try to embrace the immense at once. Do the upgrades in stages: first skin and comfort, then power and speed, which will allow you to allocate the budget and avoid critical design errors.
Frequently Asked Questions (FAQ)
What is the maximum size of the engine to be put on Ob 3M?
Officially - 30 hp However, the reinforced transom allows you to safely operate the motors up to 40-50 hp Exceeding this threshold can lead to the destruction of the aft part of the body and loss of stability on the go.
Do I need to paint an aluminum boat inside?
You don't have to paint inside if you have a good plywood skin, but if you leave the metal open, you can protect it from oxidation and make it easier to clean. Use special soils for aluminum.
Which plywood is best used for skinning?
The ideal option is a moisture-resistant plywood (PHF) that is highly durable and moisture resistant, FC (carbamide glue) is less resistant to water, but more environmentally friendly if the boat is only used on fresh water.
Can I weld the cracks in the body of the Ob on my own?
Aluminum welding requires special equipment and skills, and if you don’t have experience, it’s best to go to a professional workshop, as improper cooking can burn out the metal and weaken the structure.
Do I need to register with GIMS for a converted boat?
Boats up to 20 metres long and weighing up to 200 kg (including the engine) are not subject to registration unless used for commercial purposes, but if a major change in design (such as a cabin) is made, inspectors may have questions when checking documents.