River Crossing With a Jeep
As an opening statement it should be said that a river crossing should not be attempted by the inexperienced, especially deep river crossings. A river crossing can be fatal to an engine and even worse, to occupants of the vehicle in the worst case scenario. Never underestimate the force of flowing water. Water weighs about 62.4 pounds per cubic foot and typically flows downstream at approximately 6 to 12 miles an hour. For each foot the water against a vehicle, 500 pounds of lateral force are applied to the vehicle. As a vehicle enters water, 1500 pounds of buoyant force are produced for each foot that the vehicle is submerged. This basically means that a vehicle weighs 1,500 pounds less for each foot of water. When the buoyant force exceeds the weight of the vehicle, it begins to float and is now at the mercy of the water as the flowing force of the water is exerted on the vehicle, pushing it downstream. For typical cars, this translates into a floating car in just two feet of water. To put it into a 4×4 perspective, a 4×4 vehicle is typically lifted to some degree. This puts the buoyant part of the vehicle, mainly the body although tires are quite buoyant, higher than cars, but in many cases not by much. The key point is that like a boat, the water displaced creates the buoyancy and vehicles actually float until water seeps into them. But by the time water seeps in, it may be too late.
That being said, a water crossings in a 4×4 can sometimes be some of the most exciting and challenging situations you do when offroad. Rivers crossings can also become some of the most expensive.
A 4×4 is not an amphibious vehicle, nor is it waterproof. Even those 4×4 vehicles that have been modified to tread water have their limitations when crossing through deeper waters. The depth to which a vehicle can be submerged depends greatly on the vehicle itself. Those factors not only apply to the vehicle but the age of the vehicle as seals deteriorate. As a rule of thumb, the depth limit of a vehicle is about the top of the tires and even that is probably too deep.