The water jet upgrade is a bold step that changes the way the boat is operated. water-jet It allows you to overcome shallow water, grassy areas and even rocky tiles without fear of damaging the propeller. PVCWithout a rigid transom tunnel, the task of an amateur engineer is much more complicated.
The main challenge lies in the need to integrate the water intake unit into a soft or semi-rigid bottom without breaking the tightness of the cylinders. You will have to face the issues of flow aerodynamics, weight distribution and, of course, reliable fixation of the heavy unit on the inflatable surface. A critical parameter is the water intake angle, which in the absence of a tunnel often has to be compensated by a complex system of pipes.
Before you start cutting a transom or mounting brackets, you need to take a sober look at your technical capabilities and risks. Installation that is not only a loss of traction, but also a fatal damage to water cylinders. Let's look at the technical solutions that are available to implement this idea.
⚠️ Attention: Installing jet drive on the inflatable floor without a rigid insert (transe plate) requires the manufacture of a special podium. Direct installation on the soft bottom will lead to deformation of the water intake and loss of efficiency.
Selection of installation scheme: suspended or stationary
The first step in the project is to define the type of layout, and there are two main ways to do this: create a suspended structure that mimics the operation of an outboard motor, or put a stationary tack into the trunk of a boat, which is considered less invasive because it doesn't require the integrity of the cylinders to be compromised, but it does put limits on engine power.
A stationary installation involves inserting a water intake directly into the bottom or into a rigid transom, if it is provided by the design of the boat. For boats without a tunnel, this means creating an artificial channel for water. water-intake, which is carried out beyond the dimensions of cylinders on special brackets.
The choice between these options depends on the design of your boat. Nordic, Badger or FlagshipIf you have a low-pressure inflatable floor (LDPB) boat, you can't really do a stationary insert without completely reworking the hull, so you only have to put the hull up or put it on a hard floorboard with the water intake out backwards.
Design of the intake unit
The heart of any jet system is a water intake, and in the absence of a tunnel in the hull, you have to make it yourself, most often a rutting circuit is used to direct the flow of water to the impeller, and it is important to ensure that the flow is laminar to avoid cavitation and noise.
The intake material is usually fiberglass or aluminum. The good thing about fiberglass is that it allows you to cast a part of any complex shape that replicates the contours of a boat. Aluminum is stronger, but more difficult to process. grating at the entrance so that large objects do not fall into the impeller.
Pay special attention to the area of the inlet, which is 15-20% larger than the area of the impeller cross section, so that the pump does not "choke" at high speeds. If you use the engine from a chainsaw or a motor unit, the calculations of hydraulics become even more important, because they have limited power.
Formula for calculating the diameter of the intake
For optimal operation, the diameter of the inlet of the water intake should be equal to 1.2 of the diameter of the impeller, which provides a supply of water and prevents the flow from breaking.
Engine fastening and transmission
After the hydraulics are solved, it's the mechanics' turn. The internal combustion engine (ICE) must be rigidly fixed to the water-jet chamber. The slightest shaft distortion will cause the bearings and the glands to collapse rapidly. floppy-clutch Or a driveshaft.
If you install a system on a boat without a tunnel, it's often impossible to have a vertical shaft. You have to use angle gearboxes, which adds extra resistance points and reduces the overall efficiency of the installation, but it's the only way to lower the water intake below the water level when the motor is high.
The mounting of the entire structure to the boat must withstand vibrations and jerks when moving. For inflatable boats, the ideal solution is to use a fin plywood sling board that covers cylinders and is fixed by slings. The entire power plant is already mounted on this board.
- 🔧 Use a stainless stamp fastener A4 (316) for all compounds in contact with water.
- 🔧 Be sure to use grover washers or a thread fixator so that the vibration does not weaken the connections.
- 🔧 Check the alignment of the shafts with a laser pointer or a strained thread before the final puff.
⚠️ Attention: The use of wooden elements in the design of the transom board without high-quality impregnation with epoxy resin will lead to stratification and rotting after one season.
Sealing and protection of cylinders
The most critical moment of installing jet drive on PVC The boat is designed to protect soft cylinders from the hot exhaust pipe and possible leakage of oil or fuel, and the exhaust system should be removed as far as possible from the cylinders, and its temperature reduced by water cooling or the length of the exhaust tract.
All elements passing through the trench (shafts, control cables) must be sealed with gum knots. Even a microscopic gap under pressure from the oncoming flow will allow water to enter the boat. cuff-sealdesigned to work in a water environment.
It is recommended to install additional protective shields made of heat-resistant material between the exhaust system and cylinders, which will save the boat in the event of a silencer burning or a change in the angle of the engine.
☑️ Pre-launch checks
Comparison of propulsion specifications
To see if the game was worth a candle, let's compare the performance with a classic propeller: the watercraft loses at maximum speed on clean water, but wins in cross-country and safety. Below is a comparison table for a boat 3.6 meters long with a 5-6 hp engine.
| Parameter | The propeller | jet drive (without tunnel) | Difference |
|---|---|---|---|
| Maximum speed | 22 km/h | 18 km/h | -18% |
| Minimum depth | 30cm | 10cm | Water's better. |
| Security | Open screw | Hidden impeller | Water is safer. |
| Fuel consumption | 1.5 l/h | 1.8 l/h | +20% |
As you can see from the table, the speed loss is about 15-20%, which is often acceptable for cruising fishing, but the ability to pass overgrown ducts where the screw winds the grass instantly is a huge plus, and the lack of vibration on the boat hull makes fishing more comfortable.
It's worth noting that the data is relevant for well-designed systems. Artisanal assemblies with broken water intake geometry can perform much worse, up to complete inoperability on planing.
To improve the plane output, install transom plates (interceptors) on the back edge of the jet drive, which will help to raise the bow of the boat at low speeds.
Maintenance and winter storage
Operating a homemade jet drive requires a disciplined approach to maintenance. After each release, especially if you swim in dirty or sandy water, you need to wash the inner chamber with fresh water. The sand, settling on the impeller blades, disrupts the balance and causes the shaft to beat.
Before long storage, lubricate all movable joints and glands with conservation lubricant. The engine should be preserved according to the manufacturer's instructions. You can store a boat with a jet drive installed, but it is better to dismantle the heavy unit to reduce the load on the cylinders and the transom board.
Check your condition regularly impellerWhen hitting rocks or logs, the blades can get chipped, which will cause a drop in traction. Repairing an impeller often requires a complete replacement, so having a spare part in the garage is a reasonable precaution.
The main secret of the durability of the jet drive is regular washing from the sand and checking the gaps between the impeller and the fairing. The gap should not exceed 0.5 mm to maintain efficiency.
Can I install a jet drive on an inflatable floor boat (BBB)?
Theoretically, you can, but it's very difficult. You'll need to make a hard false floor (podium) that will take over the load from the engine and the water intake, and without a hard base, the soft bottom will deform under water pressure, which will lead to loss of tightness and controllability.
Which engine is better to choose for a homemade jet drive?
The best choice is considered to be engines from motoblocks (type) Lifan, Loncin) 6-9 hp They have a horizontal shaft, which makes it easier to dock with the pump, and are quite reliable. Chainsaw engines require complex gearboxes and are less reliable when working at constant speeds for long periods.
How much will the fuel consumption increase after the installation of the jet drive?
Fuel consumption is usually increased by 15-25% compared to propellers of the same power, due to lower efficiency of the jet propeller at low speeds and losses on the friction of water inside the pipeline, but overgrown water bodies can be more efficient jet drive due to the lack of need for frequent cleaning of the screw.
Do I need to register a boat with a homemade jet drive in GIMS?
Yes, if the engine power exceeds 8 kW (about 10.8 hp) or the weight of a boat with an engine exceeds 200 kg. Homemade installation does not exempt from registration. Moreover, inspectors may take an increased interest in the safety of your design, so stock up drawings and certificates for the components used.