Metal flat-bottomers of the Ob series have been a legend of domestic small-scale shipbuilding for more than half a century, occupying a strong niche in the arsenal of fishermen and hunters. weightIt is one of the most discussed on profile forums, since the choice of the motor, the type of trailer and the physical possibility of transporting the boat directly depend on this parameter.
The factory specifications listed in the technical data sheet are often different from what scales show after decades of operation and modernization. In this article, we will discuss in detail what the body mass is made of, how the thickness of the aluminum alloy affects the final figures and why. weight It can significantly exceed the declared 145 kg.
Understanding weight specifications is necessary not only for logistics, but also for calculation. stability An overloaded or improperly hung boat becomes dangerous, especially when riding a wave or in sharp maneuvers, so the numbers in the documents should be treated as a basic guideline, not as an absolute truth.
Factory specifications and data-sheet figures
According to technical documentation developed in Soviet times, the weight of the hull of the boat “Ob” without engine, equipment and equipment was 145 kilograms. This figure is relevant for classic models made of aluminum-magnesium alloy AMg5M. corrosion resistance And the strength of a relatively small specific gravity.
However, it should be borne in mind that in different years of production, the technology could change. If in the 60s and 70s, the thickness of the skin was strictly monitored, then in later periods or in the production of private copies, the thickness of the sheet could vary according to the drawings. The standard thickness of the bottom and sides was usually 2 mm, but reinforced versions could have a skin of up to 3 mm, which automatically increased the weight by 20-30 kg.
⚠️ Warning: When buying a used boat, don’t blindly look at the numbers in your passport. Over the decades, the hull could have been overgrown with layers of paint, epoxy resin, additional bulkheads and runducts, which significantly increased its actual weight.
It's important to distinguish between body weight and kerb weight. Passport 145 kg is just naked aluminum. full-bodyready to be launched, you need to add the weight of the transom, seats, fasteners and attachments, which in total gives completely different indicators.
Factors that affect the actual weight of the boat
The actual weight of the Ob M is a variable variable that depends on a variety of factors. The first and most obvious is the state of the metal and the presence of additional structures. Many owners independently reinforce the bottom, weld additional stringers or install a full-fledged one. timberThis inevitably leads to an increase in mass.
The second factor is accumulated garbage: the inner cavities of boats, especially those stored outside, are often filled with water, mud, sand and residues of fishing gear. Even a few liters of water lingering in the bow or in the corners of the cockpit, can add 5-10 kg to the total weight, which will significantly affect the weight of the boat. transportation.
- 🛠️ Refinements to the hull: Installing a keel strip, additional bulkheads, anchor boxes and rundooks under the seats adds 15 to 40 kg.
- 🎨 Coverage: Multilayer application of epoxy soils, anticorrosion compounds and paint can increase weight by 5-10 kg, especially if heavy asphalt-based compounds were used.
- ⚓ Fixing equipment: Stationary fixed ducks, linear racks, sonar brackets and spinning holders, even being small, in total give a tangible load.
Effects of metal thickness and type of alloy
The classic Ob was made of an AMg5M alloy, which had excellent weldability and strength. The density of this material is about 2.6-2.7 g/cm3. At a standard sheet thickness of 2 mm, the weight of one square meter of skin is about 5.2-5.4 kg. Multiplying this by the surface area of the boat, we get the base mass.
However, if you consider a reinforced bottom (3mm) or a boat welded from a thicker sheet to increase survivability, the weight specifications change dramatically. A thickening of just 0.5mm around the hull will add more than 10kg to the boat's weight. This is critical if you plan to use it. low-power Or transport a boat on the roof of a car.
There are also versions that used the D16T alloy, which is stronger but less resistant to corrosion and requires more careful protection. The weight difference between the alloys is minimal, but the difference in manufacturability and the need for additional processing (grounding, painting) can affect the final weight of the finished product due to the thickness of the protective layer.
| Parameter | Standard (2 mm) | Reinforced version (3 mm) | Difference |
|---|---|---|---|
| Weight of 1 m2 of sheathing | ~5.3 kg | ~7.9 kg | +2.6 kg/m2 |
| Approximate hull weight | 145 kg | 190-200 kg | +45-55 kg |
| Cargo capacity (passport) | 400 kg | 400 kg | No change. |
| Recommended engine power | up to 12 hp | 15-18 hp. | More HP is needed. |
Weight in the assembly: engine, tank and equipment
When we talk about transporting a boat, the weight of the naked hull is the least of our concerns, and the main task is to figure out how much mass you have to lift onto a trailer or drag into water. The standard outlet kit includes the boat itself, the outboard motor, the fuel tank, the anchor, the life jackets and the fishing gear.
A 9.9 hp outboard motor weighs an average of 27-30 kg (two-stroke) or 35-40 kg (four-stroke) or a 12-liter fuel tank adds about 9 kg of fuel weight plus the weight of the canister itself (about 1 kg). If you add the weight of the transom plate (if it is removable and heavy), anchor (5-10 kg) and the minimum set of gear, you get a significant increase.
Thus, the total weight of the set “Ob M” with a 10 hp engine and minimum equipment will be:
- 🚣♂️ Boat hull: 145-160 kg (including improvements).
- 🚜 Motor (2T 9.9 hp): 28 kg.
- ⛽ Fuel tank: 10 kg.
- 🎒 Equipment and crew (2 persons): 160 kg.
- 📊 Total displacement: ~350-370 kg.
As you can see, even with a minimum set, we come to the limit of rated carrying capacity of 400 kg. weight-weighting The inside of the cockpit is critical to safety.
Load capacity and mass distribution
The Ob has a passenger capacity of 400 kg, which means that it can accommodate three people of medium weight and a small amount of cargo. However, in practice, especially with a wave, the safe load should be less than the maximum. float-stock And it becomes a roller.
It is critical to distribute the mass correctly along the length of the body. Ob is a flat-bottom with relatively sharp cheekbones in the nose. Shifting the load (motor, passengers, luggage) into the nose can cause the cheekbones to bury in a wave and flood the cockpit with water. Shift in the stern, on the contrary, can cause yaws and reduce the efficiency of gleaming.
⚠️ Warning: Never place heavy loads (batteries, catch boxes) in the bow of the boat without a reliable mount. When hit by a wave, the loose load can shift, leading to a sharp roll and potential rollover.
The best option is to place heavy items (fuel tank, battery) near the diametric plane and closer to the stern, but not on the transom itself, so as not to pick up the nose.
☑️ Checking the load before exit
Transportation and fibre specifications
The issue of transporting the Ob M is directly related to its weight. 145 kg is a significant mass that cannot be carried alone over long distances. To move on hard ground or concrete, special roller carts are usually used, which allow one person to tow the boat.
When loading on a trailer or roof, weight becomes even more critical. If you plan to put a boat on the roof of a passenger car, make sure that the dynamic and static load on the rails allows you to lift more than 150 kg (taking into account the weight of the boat itself and the weight of the bottom / engine).
The sloping method is often used to launch from a sloping shore, where the weight of the boat is felt most acutely. The aluminum bottom has a high coefficient of friction against sand and pebbles, so they use special runners to facilitate the process or just wait for a partner to help. It is quite possible to carry a 150-kilogram boat together if you take sides and synchronize your steps.
Comparison with peers and competitors
To understand whether the Ob M weighs much or little, let’s compare it to other popular metal boats: the classic Kazanka (designed in 1960) weighs about 130-135 kg, which makes it slightly lighter than the Ob, but also less spacious. The Crimea, on the contrary, is heavier – about 160-170 kg, but has a more seaworthy hull.
Modern 2mm thick AMG boats often have a weight comparable to the Ob, but due to the improved geometry of the bottom and the use of light alloys (AMg6) can be lighter at the same dimensions.
The table below shows a comparison of the masses of popular domestic metal boats:
| Model boat | Body weight (kg) | Load capacity (kg) | Materials |
|---|---|---|---|
| Ob M. | 145 | 400 | AMG5M |
| Kazanka (project) | 130 | 350 | D16AT |
| Crimea | 165 | 400 | AMG5M |
| voronezh | 115 | 300 | AMG |
The Ob M is thus in the middle of the weight of classic Soviet metal boats, offering a good balance between durability and mobility.
FAQ: Frequently asked questions
Can the weight of the OBM boat be reduced?
It is difficult to drastically reduce the weight of the already finished boat. You can remove excess attachments, replace heavy wooden elements (seats, tanner board) with lightweight composite or aluminum analogues, and remove excess layers of old paint and anticork.
Which motor is better for Obi in terms of weight?
The Ob's optimal traction/weight ratio is the 9.9 hp (about 27 kg) two-stroke motors, which easily lead the two-passenger boat to plane. The four-stroke motors will be heavier, which may require more careful weighting.
Will the Ob M hold three men?
Formally, a 400 kg load capacity allows you to accommodate three people (80 kg = 240 kg) plus 160 kg of cargo. However, in practice, it is safer to limit yourself to two passengers when you are excited to maintain buoyancy and stability.
How different is the real weight from the passport?
The difference can be anywhere from 10 to 50 kg upwards, depending on the year of manufacture, the number of paint layers applied, the presence of welded reinforcements and the amount of moisture and dirt absorbed into the structural cavities over the years of operation.
Can I put the boat Ob on the roof of the car?
Technically, you can do it if the roof and rails are designed to carry a static load of more than 150 kg. However, it is extremely difficult and dangerous to raise such a mass to the height of the roof alone, and this requires special lifting mechanisms or the help of several people.