(original post by HEOehlke@webtv.net on 16-MAR-2003)

I have been researching a suitable hovercraft to purchase or build as a fishing vessel. I appreciate Neoteric as the only manufacturer I have found so far that would publish information concerning maximum passenger loads that their craft could effectively lift "over the hump" from a dead start in the water. Most other manufacturer list only maximum hard surface loads and tend to avoid this subject when questioned. Does your new Hirth 65HP option motor improve this performance ? Are there other accessories (veri-lift devices ?) or manuevering techniques that could help in this area ? Realistically, what is the most payload I can hope to accelerate over the hump with an ideally outfitted side by side seat Hovertrek ? This will help in my decision to finally purchase what I think is the best value HC on the market.

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(original post by neoteric on 27-MAR-2007)

To say that "hump drag" is complex is an understatement. Some of the variables affecting hovercraft hump drag are weight, speed, plan form shape, length, density of water, depth of water, wind, waves, pressure gradients inside the cushion, trim, and thrust. For a lightly loaded hovercraft with a lot of thrust (such as for a racing hovercraft) hump performance is irrelevant. But, for heavy craft with a smaller thrust to weight ratio, hump performance is of major importance. To our knowledge, there is no variable lift device which helps improve hump drag performance. There are several techniques taught in the Neoteric pilot training which help to overcome hump drag, but they are too involved to discuss here. If the plan form shape has an aspect ratio (this is defined as the width squared to the craft plan form area, which reduces to the ratio of the width to the length for a rectangular hovercraft) of 0.5 or less, then the most important factor is a high thrust to weight ratio. Some racing craft approach a value of 1, but most recreational machines are around 0.25 or less.

If a larger motor results in increased thrust without increasing the hovercraft weight by much, then the hump performance will improve. Such is the case with the 65 HP engine.

In average wind and sea states, you can expect to accelerate 900 lb over the hump at full power with a 65 HP engine.

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