Features Not Found on Most Other Homebuilt or Manufactured Surface Skimmers
- Raised bow and stern improves rough water and rough terrain capability. The Vanguard based sevs will ride up and over obstacles that would be struck by many other craft.
- Large diameter, lightly loaded rotors yield high performance with low fuel consumption. Rotor tip speeds are kept at the lowest levels in the industry, resulting in reduced rotor noise, and virtual elimination of propeller and fan blade leading edge erosion caused by sand and water. Adjustable pitch composite rotors with individually replaceable blades may be purchased from Sevtec or from other suppliers.
- Two compartment air cushion reduces vehicle sensitivity to changes in loading and changes in power settings. The forward cushion has controllable pressure to aid in turning and stopping. Large surface skimmers pump fuel into fore and aft tanks for pitch trim, which is too slow to be effective for small skimmers. Other small surface skimmers use an elevator surface, which is mounted in the propeller air blast. This type of control is effective only if near full power is applied, or the craft is at high speeds. This leaves the craft without effective trim for ninety plus percent of its operations, when it is cruising and exploring. In a Sevtec, you just move the seats for optimum trim.
- Special bow skirt design minimizes spray while allowing high skirt air to ground gap. Most small skimmers use a single compartment air cushion. When the craft comes up on plane, the bow skirt lifts and the craft occupants are inundated with water spray. The double compartment controllable cushion on the Vanguard derivative sevs holds the bow down and eliminates almost all of the spray. This feature is very important when operating in cold weather and even makes cold weather operation reasonable without a windscreen.
- Forward cushion compartment pressure can be directly controlled by the operator for improved maneuvering and stopping. The operator may lower the craft nose to increase drag to assist stopping and turning by opening the ports and allowing air to escape from the forward cushion. The sev can also be rolled into a turn for better steering using the planeout wave, when power is reduced to round a turn, making Sevtec sevs the most maneuverable surface skimmers available, homebuilt or manufactured.
- Single engine design provides lowest cost, greatest reliability, and easiest operation. While it may seem logical to have the propeller and fan driven by separate engines, and indeed, such vehicles are far easier to design than single engined craft, the reality is that a twin engine craft is more difficult to operate, as it is nearly impossible to coordinate lift and thrust engine power settings. Operating experience with two Sevtec designs and the designs of others has definitely shown that multiple engine installations should be left to large craft. However, the controlled fore and aft cushion setup reduces two engine control problems markedly.
- Uncluttered floor area gives maximum room, and ease of cleaning the sev after use. There are no nooks and crannies around ribs and longerons or other structure to clog and get in the way of seating. Seating is easily removable for carrying people or cargo or camping on land. There is even enough room in Scout to stretch out on the floor for a snooze!
- In all Sevtec designs, even the smallest, you sit comfortably with feet out in front of you, and with a backrest. There is no need to be hunched over handlebars, or to throw your weight around to steer. This feature, coupled with low noise levels and great fuel mileage allows long cruising and exploring trips not practical with other surface skimmers.
- You can easily dive overboard and climb back into the stable Vanguard sevs when they are floating, which is not the case with most small sevs. (This should be practiced in good weather by any small sev operator.)
- The composite rotors are not only resistant to erosion by sand and water, they do not deteriorate when left out in the weather. When it comes to saving money on a sev, the rotors are not a good place to compromise, as you will have to replace them.
- Builders of wood fixed pitch rotors usually end up building two or three propellers before getting things right, the variable pitch rotors sold by Sevtec eliminates this problem. Wood used in the Vanguard sevs is well covered and protected in the hulls, which are mostly of composite foam and fiberglass construction. Surveyor and Geoduck are wood free designs, and high density foam may be used in place of wood in the Prospector, Explorer, and Mariner, if desired for damp hot moist climates and outdoor storage.
- Single or two engine design places all of the noisy components behind you, reducing noise and giving you an unobstructed view over the bow.
- Only a little, brazing is required on Scout, making it an ideal school project, with exciting performance. No machining , some brazing is required on Vanguard. Larger designs require minimal machining to adapt pulleys to the builder's engine and the larger sevs require some brazing, no welding, of metal parts.
- While small hovercraft frequently use a single rotor to provide both lift and thrust, the sev uses separate lift and thrust rotors so that optimum efficiency may be obtained for both cushion air generation and thrust. While some small hovercraft use separate lift and thrust rotors, they normally use an engine for each rotor. While this may ease engineering problems and gain efficiency, it poses a real reliability problem, as the engine is the most unreliable part of the craft. Smaller sevs use only a single engine which drives both lift and thrust rotors, and where two engines are used on larger sevs, unlike some larger hovercraft, the sev can still be operated should any one of it's engines fail.
- One thing that is not used on the Sevtec sevs is a duct, or shroud around the propeller. The duct is commonly used on the hovercraft, but numerical analysis and measured performance by the designer shows plainly that while the duct can improve performance on a hovercraft with a small diameter rotor, it is hard to build and may consume as much time as the hull construction. There is an advantage for a manufactured craft, however.
Look for the above features when looking for a surface skimmer project, or are looking to buy a surface skimmer. If practical, go for a ride, before selecting a project.
The Sevtec prototype Scout and Vanguard sevs. Surprisingly enough, the small sevs are the hardest to design for high performance. What appears to be a duct on Scout is a ring guard.
The Sevtec sevs are a generation ahead of any other surface skimmer, home built or manufactured, and one might see the advantages as above work into the designs of others, when the designers discover the Sevtec sev.