PWC hulls (as well as most recreational jetboat hulls) are what is known as "planing" hulls, meaning that with sufficient power, they rise to the surface of the water and actually skim or "plane". How? Physics!! As a hull moves through the water, it forces the water it comes into tact with downward. That's the action. The reaction? The water pushes upwards against the hull, creating lift.
At low speeds, your pwc acts like a "displacement" hull, plowing through the water supported by the weight of the water supported by the weight of the water it is displacing. This is refferred to as static water pressure. Pick up that speed, and your Jetski is designed to rise to the water's surface using lift, where it skims along with much less drag, supported by the water's velocity pressure.
Jetski Hull Terminology
The V of hull refers simply to the hull's angle when viewed from the bow, or the front of the boat. Curving in from each side of the rub rail and joining at the bottom center-line, or "keel" most all hull shapes form a "V". If the hull sides meet at a sharp point at keel, the design is referred to as a Full V, and will typically offer a smoother rough-water ride due to its ability to "slice" through the water. It may however, sacrifice some stability due to its tendency to roll with the waves.
That same deep V can also produce drag, leading many PWC manufactures to choose a modified V, a design that flattens as it moves aft, from the bow to the stern, or the rear of the boat. The goal? to retain some of the benefits of a V hull, while improving stability (and often speed) by placing a flatter surface in the water.
The angle of the hulls "V" is refered to as the deadrise, and is measured in degrees. Simply put, deadrise is the angle at which the hull sides curve away from the horizontal.
As you might expect, A shallower hull angle will typically produce better speed, planning easier than a deeper angle. These sharper deadrise hulls, however, will typically offer better handling due to their ability to slice more easily through the water. They will, however, sacrifice some stability in the process.
Yes, Most hull designs feature a deadrise that changes as you travel away from the bow torward the stern, resulting in a sharper degree deadrise around the bow and amidships area that flattens as you move backwards. The goal? To combine aggressive handling with a stable ride.
Follow the hull sides downward from the bondline and you'll notice a point where the shape angles rather dynamically, a point where the hulls more vertical sides and the hulls angled bottom actually meet. This is whats known as chine.
Chines determine a great deal about a hulls handling. ability, as well as its directional stability. Softer chines (those with a more gental angle) will result in hull that rolls more in a turn. Most Jet skis feature sharper chines that will produce a greater hook to the turns, as their greater angle provides a better "bite" into the water.
a chine's position will also affect the sharpness of a turn. typically, the lower the chine is placed on the hull,the quicker turn it will help produce.
Often thought of as "rails" running length wise along the hull bottom, strakes are raised "lines" in the hull that produce lift. How so? when accelerating from a dead stop in the water, water is forced outward from the keel and is pushed against the strakes, where its force then lifts the boat and helps it to plain. Once the craft has planed,strakes help the hull to ride on less of its surface area, improving overall speed.
Typically the greater number of strakes used on the hull, the lighter and flatter the hull will run in the water. To much lift, however, and stability suffers, as to little of the hull area remains in contact with the water. Sharper, larger strakes can also prevent the hull from sliding out in the turns, but again, a proper balance is the key.
All the rage in offshore powerboats, steps are cut into the hulls of some PWC to create additional points of lift, and reduce the "wetted" area of the hull.
as water flows along the hull, its lift is greatest at the hulls leading edge, then lessens as it flows toward the stern. Eventfully the force of the water becomes drag. By placing steps into a hull, designers in effect create additional leading edges, making hull plane quiker.
The "fins" or "rudders" typically attached to the hull sides at the stern of your boat or Ski, sponsons can significantly improve the handling performance of a watercraft by keeping the stern hooked to the watercraft by keeping the stern hooked to th water during turns. Today, sponsons primarily come in two shapes:
A hooked fin or a paddle type rudder. In general, the larger and deeper the design cuts into the water, the more aggressive the ride becomes.
A PWCs ride plate is the piece of metal or composite material that covers the jet pump area (pump cover) of the stern of your Jet Ski. But, more then just a protective plate, a ride plate can determine a great deal about your ride, as its the lone spot on your machine that is almost always in contact with the water.
Designs can add "hook" to your jet Ski, forcing the bow deeper into the water, or aid in tracking with multiple grooves. They can be reduced in angle to improve top speed.
an area that is becoming increasingly important is the intake portion of your hull design, the pocket where water is sucked up into the jet pump.
Enter the intake grate, in esscence a protective set of bars to shield the intake from sticks and rocks.
Intake grates can do more, than simply protect your impeller or pump. They can help load it with water, typically by adding a "scoop" to the grate that protrudes lower into the water. But the grate scoop creats drag, lowering your speed.
Jet Ski News & Jet Boat
Jet Ski news & Jet Boat info for Yamaha Waverunner Sea Doo Polaris Jet Ski Honda pwc & Boats. Including: events, racing clubs, models manufactures Impellers props and boating. A watercraft PWC Jetski Magazine.