6 Things You’ve Always Wanted To Know About Hull Design… But Were Afraid To Ask

Peruse the typical personal watercraft review and you’ll inevitably find mention of a PWC’s hull design, and how it impacts the craft’s handling. All too often, however, the descriptions are brief, or worse, assume the reader has a naval architect’s knowledge of hull terminology.

Don’t know your keel from your chines…or just want a little better understanding of how the hull affects the resulting ride? Here are the six key terms you should know:

1. V, Modified V — Probably the most commonly used term when someone is attempting to describe a hull shape, a hull’s V is simply the angular shape the hull forms as it curves from the port and starboard sides down to the keel, that centerline at the very bottom of the hull. Having trouble finding it? View the craft out of the water directly from the front or back. You’ll note a pronounced, V-like shape to the hull.

The sharpness of that V says a lot about the ride that hull will deliver. A sharper angle, often dubbed a “deep-V” hull, will excel in rough water, allowing the hull to slice through waves and deliver a less-jarring ride to the passengers above. One tradeoff, however, is stability. As you might expect from that sharp angle, a deep-V craft may tend to roll more from side to side. A hull with a more gradual V may be far more stable and fast, but it sacrifices agility, and can deliver a more punishing ride in rough conditions

To get the best overall ride, most PWC designers today choose what is known as a “modified-V.” Towards the bow, the design maintains a deep-V’s sharp angle to slice through the waves. As you move aft along the centerline, that angle of V decreases to enhance stability and top speed.

mod V 1_blog
(photo credits: www.personalwatercraft.com)
2. Deadrise — Occasionally, you’ll hear the actual angle of that V expressed in a measurement. That angle is known as the hull’s deadrise, and can be measured at any point along the hull from fore to aft. Example? Sea-Doo’s GTI is known for its 16-degree deadrise, which makes the boat a little more loose and playful than most of today’s models. In contrast, Kawasaki’s Ultra 300/310 models are known for their deep, 22.5-degree deadrise, one reason why they excel in tough, offshore conditions.

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(photo credits: www.sea-doo.com)

3. Chines — One feature that determines a lot about how your craft behaves in a turn is its chines, the corners where the vertical hull sides takes an abrupt turn then angle steeply inward toward the keel. If this angle is soft and rounded, the craft will roll intuitively into a turn with a nice inside lean, but sacrifice a little stability. If this angle is sharp and severe, the hull will be more stable but not roll as easily into a turn.

Chines_3

(photo credits: www.personalwatercraft.com)

4. Strakes — Those raised, lengthwise ridges located between the chines and keel are known as strakes, and are added to the hull to create lift. As your craft accelerates, water is pushed to each side of the keel. Rather than just let it slide off the hull, strakes trap some of that water and use it to lift the hull and push it more quickly onto plane. Once on plane, strakes allow the hull to ride on less of its surface area, increasing top speed.

Hulls can have multiple strakes per side. Adding additional strakes is thought to increase speed, as the hull will run higher and flatter on the water. Go too far, however, and you’ll lose stability.

Strakes also play a role in tracking. Like mini fins, they prevent the hull from sliding in a turn.

Strake_4

(photo credits: www.personalwatercraft.com)

5. Step — Several PWC models incorporate a step, or distinct side-to-side ledge across the hull. In theory, it’s a way to increase speed. As water flows along the length of the hull, it provides the greatest amount of lift at the hull’s leading edge. By the time it reaches the stern it has lessened dramatically, to the point it actually creates drag. Steps add a second leading edge along a hull’s length to create additional lift. The hull should plane faster, have a better top speed due to the reduced wetted surface, and as water coming off a step is aerated, experience less drag.

Like all hull design, however, adding a step is a balancing act. Proper placement is essential to avoid negatively impacting the craft’s handling.

 6. Sponsons — Sponsons aren’t a feature of the hull itself, but rather a bolt-on addition to the aft, vertical hull sides. They provide some lift and stability, but their main purpose is to improve handling by acting like an outboard rudder. Placement is key. The deeper and further toward the stern the sponson is located, the more aggressive the ride.

sponsons_personalwahtercraft.com_

(photo credits: www.personalwatercraft.com)

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