How Does a Jet Boat Work

Using an engine to stream water through a turnable nozzle that adds steering.

Jet Boat Engines

The engines used by modern jet boats are lightweight and compact. Thus they allow for more than one engine. Jet boats which are 21 feet or longer get fitted with two engines as well. This acts as security in times of engine failure and gives more power. It also provides:

·        More acceleration and less cavitations than the other powered single engine platforms.

·        With the engine situated low in the hull, there is tons of space for the designers to work with. This can be used for additional storage and seating options, making it more user-friendly.

 

Jet Stream

The tail portion of the water jet extends out through the transom of the hull, above the waterline. This jet stream exits the unit with the help of a small nozzle at high velocity which helps in pushing the boat forward.

One of the most significant breakthroughs in the development of the water jet was to go for a design which would expel the jet stream above the water line. It was Hamilton who found that this greatly improved the performance which gave a clean hull bottom, which allowed the boat to skim through very shallow waters. It should be noted that while it makes no difference in the amount of thrust generated, but having it above the waterline reduces hull resistance and draught.

 

Steering

By moving the nozzle to either side or by small gates on either side which deflect the jet stream the boat is steered. It should be noted that the jet boat relies on the flow of water through the nozzle for control and as such, it is not possible to steer a conventional jet boat without the engine running.

Jet boats are used for adventure tourism and are a common sight in coastal and river tourism activities. People generally buy them for high-speed thrills, and they certainly deliver on that. However, caution should be taken that since the engines are small and the boats light so bringing them into deep waters of the oceans and such us not advisable at all.

The boating industry has witnessed a significant decline in sales over the years following the recession, but one type of boat witnessed steady growth and still does it is the modern jet boat. Sir William Hamilton initially designed jet boats for operating in the shallow and fast flowing rivers of New Zealand. It is a vehicle that is propelled by a jet of water which gets rejected from the back of the craft.

It was only at the beginning of the 21st century that the jet boat became modernized and appealed to the masses. Specifically when Yamaha introduced a new hull design paired up with the Yamaha 4 stroke fuel injected power plants. These new models were quiet and were clean regarding emissions which were also tens of thousands of dollars.

The biggest jet driven vessels are found in the military generally. Some examples are South Africa’s Valour-class frigate (120 meters long) and the United States Littoral Combat Ship (127 meters long), these are the biggest jet-propelled vessels.

 

Water Jets

In a jet boat, a water jet draws water present right beneath the hull where it passed through a series of stators and impellers known as stages. These work to increase the velocity of the water flow. Nowadays, most modern jets are single stage while older jet boats had as many as three steps. A jet boat draws the water from under the ship with the help of intake and sends information to a pump jet inside the boat. This mechanism is unlike a motorboat or a powerboat that uses an external propeller behind the boat or in the water below. Hamilton designed it as such to specifically overcome this problem of propellers striking rocks in the waters. This allows for a couple of benefits:

·        The contained spinning wheel means that swimmers are safer.

·        The propulsion produced on the lower end is greater than the traditional ones. This is because, as the impeller becomes more efficient when contained within the housing and all the force which gets created is propelled rearward is ultimately used for propulsion. In contrast, traditional propellers lose a bit of their efficiency around the tips of the blades which results in less thrust at slow speeds.

·        The contained propulsion system is placed within a housing, which again is encased inside the hull of the boat; this makes the jet boat not require as much water depth as the traditional stern driven ones to do. This also allows for less propulsion system damaging and as well as safer boating in more shallow areas.

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