Hull Technology in Hydrostream boats

by Virus


When discussing hull technology, we must consider many variables that formulate the performance potential of a particular hull, and how this performance should best be exploited. Some things to consider are propeller type and size, hull weight and size, setback, amount and weight of the power unit, the situations the hull will be used in, water conditions, and of course, the hull design itself. For purposes of this discussion, we shall focus on the V, XT, and YT bottom designs.

It all started with the padded V-bottom we are all familiar with. The V-bottom is basic in design, and very efficient from a physical standpoint. Hydrostream introduced several versions Jim Wheaton's Valero V-bottom. of this, but basically they belong to two categories Ė hooked and non-hooked. Generally, the padded V-bottom hull requires less horsepower to achieve satisfactory performance than its counterparts. Why is this? By design, the V-bottom hulls are lighter, and have the least contact area with the water at moderate to high speeds. In other words, they are the "driest" hulls. At speeds above sixty mph, the hull starts to "ride" on its pad, allowing the rest of the hull to ride above the water, parting the wind. Typically, a Hydrostream V-bottom hull running at eighty mph and above will be riding on about twelve to sixteen inches of the length on its pad.

This design, although highly efficient, has one drawback Ė itís extremely unstable at high speeds to the novice user. Beginning at about sixty mph and becoming exponentially worse as speeds increase, the hull will "chine walk" as the user brings the hull up on its pad. This has the effect of the hull swaying on its keel, and the user must counteract this effect with steering and trim input. If left to its own devices, this can become extremely dangerous, and without constant and proper user intervention to maintain control, the user can lose complete control of the rig. What forces are involved in chine walking? Basically, the user is attempting to balance the hull on the center pad, while the water passing by the lower unit is trying to "eject" the lower unit from the water. Many hours of careful practice are required to safely execute the operation of a V-bottom hull at very high speeds.

Finally, the worst nightmare of all Ė blowing over. The V-bottom is very sensitive to trim input, and applying too much positive trim and power at the same time can cause a blow over. These hulls are extremely light, and the wind must be considered when applying trim adjustments. Many people tend to "hang" these hulls too high; thinking that higher is better, when in fact this is quite contrary to the truth. More on this laterÖ

Performance is fast, and V-bottom hulls generally cut through chop well, however, the lightweight of these hulls can be counterproductive to a comfortable ride in anything more than a modest chop. Generally, these hulls corner turns well, however, on tight maneuvers these hulls tend to slide the stern, and cannot offer the "on rails" handling of the YT and ZT hulls.

In the early seventies, Hydrostream sought to make its hulls safer for the average boater by the inclusion of a "hook" in the pad at the stern. This design was used on the Viper, Vector, Verado, Varmint, and Vamp. The hook added a trim tab effect to the hull, forcing the bow down as speeds increased. Although this safety feature did not completely prevent blowovers, it did make the hulls more tolerable to the masses. These hulls did take a performance hit as far as top speed is concerned because of this, however, as many came to realize, adding significant horsepower increases over rated maximums, setback units, and sometimes filling the hook in (or removing it) added greatly to the performance potential of these hulls.

In 1976, OMC introduced their 200 hp V6, and a year later, Mercury introduced the 175 hp Black Max. Hydrostream went to work on a hull that would handle the extra power and weight of these motors, and a hull that more experienced users can exploit. That culminated into the 1978 Viking Ė a non-hooked V-bottom. Better balanced than its predecessors, and much safer at ultra high speeds, this hull set the standard for many performance boaters and boat companies. The non-hooked design carried over to the Vulture, Vegas, and Venus. Itís no wonder a Viking will achieve higher speeds than a much lighter Viper with the same power.

Ideally, the Viking should run well with a minimum of five inches of setback and V6 power. For hulls with more than 230 hp, a cleaver is recommended, otherwise, use a roundear-style propeller. Upon acceleration, the user should start trimming out gradually, starting from a level plane in the sixty mph range. Positive trim should be applied until the hull "breaks away", and then leveled off as full power is applied. More trim than this, and youíre compromising your performance as well as safety. With the proper setup, these hulls will attain speeds of over 100 mph with 240 hp or more.

From here, we move on the YT hull. Basically, this was the hull that was supposed to add greatly to safety for the beginning user because of its very forgiving nature and full sponson support.A good look at a YT bottom as Austin Plyem rockets out of the hole in his Valero YT Bowrider. The YTís sponsons are level with the bottom pad, meaning that the hull rides on three "wet points" at high speeds. These hulls will require more hp than itís V-bottom sibling to achieve similar performance, however, stability and cornering are the staples of this hullís character.

These hulls do not fly as easily as V-bottom hulls, and will require 175 hp or more for satisfactory performance. A minimum of six inches of setback is recommended, and unless 230+ hp is on your transom, youíll need the bow lift of a roundear to get that boat to move. Typically, these hulls will break away at 70-75 mph, and in some cases, requires more than modest positive trim to facilitate this on lower-horsepower rigs. Although this is a modified tunnel design, it will chine walk at speeds approaching eighty mph. Typically, the motors are set slightly lower in the transom than a V-bottom configuration. In my experience, a hydraulic lift plate is most useful on these hulls, since they are very sensitive to weight changes. Adding a passenger? Just lower the motor to help that rig break away. Finally, these hulls are much less susceptible to blowing over. Added weight, better under-hull air management, and a low bow stance all contribute to this hull being among the safest hot boat rigs on the water.

Cornering performance is superb, and taking turns in this hull will almost make you forget that youíre on water. Tight high-speed maneuvers can be executed with confidence, and the stern behaves by tracking extremely well. Rough water handling is also great, thanks to the large, deep sponsons. These hulls can fly over small chop at eighty mph with little difficulty.

Lastly, the XT hull is basically a synthesis of the V and YT designs, incorporating modest sponsons and a center pad. The sponsons are not level with the pad, resulting in great stability and maneuvering ability at low speeds, and the efficiency of a V-bottom at higher speeds.

When the XT hull attains speeds starting at sixty mph, the outer sponsons will rise above the water, also adding to hull lift as they trap air in the tunnel passages. After this, the same care as a V-bottom is required to maintain an even keel and safety at high speeds.

I found this design to add greatly to performance ability in the twenty-foot hull designs verses the V-bottom. The added lift from the air-entrapment qualities of the XT hull help offset the added bulk of the larger hull; however, do not underestimate the lifting capabilities of the XT design. Without proper user intervention, the Vegas or Venus XT will run away from you. Those hulls will fly! This is truly a performance solution for those who want great stability at low speeds, and want to open it up when the situation calls for it.

As usual, when running with 200 or less hp, a chopper-style roundear is most effective for the Vegas and Venus hulls. The chopper carries weight well, and best utilizes the motorís horsepower. When running with Bridgeport or 2.5 power, consider a cleaver-style propeller. As with the YT, the added horsepower will provide enough load-carrying ability to start taking advantage of the cleaverís stern-lifting ability. I can only wonder what a Viking XT would have been likeÖ.