In a message dated 10/2/03 6:37:02 AM Pacific Daylight Time, buchner@wcta.net writes:
He was using a Honda motor sized big
enough, and with a belt drive, which allowed him to run the engine at
*idle* and get useful output. Quiet!
I totally understand the appeal of low-noise output, especially when it comes to residential applications, but running an IC (internal combustion) engine at idle is anything but *efficient* in terms of power-to-weight ratios and fuel consumption. With few (if any) exceptions, IC engines have a narrow RPM band where they are most efficient. Assuming that the IC engine will be used only to charge the batteries and not as a secondary motive force, current hybrid-electric design ideology tends to size the IC engine according to the smallest and lightest choice that, operating at its *peak efficiency*, will produce the required output for the application. Once you drop the requirement that the engine be functional over a broad RPM range, as is the case with primary propulsion, your options and efficiencies increase dramatically.
From an engineering design standpoint, it's been encouraging over several months of lurking to hear members periodically bring up technologies (e.g., stirling, solar) and methods generally considered "fringe". Even if some of them are impractical within the context of submersibles, the willingness to at least *consider* them as design solutions is nothing less than the stuff of DaVinci. Inspiration and open-mindedness are oh-so-unfortunately not something that can truly be taught in engineering school.
I have to confess that, as an engineer, the thought of "amateurs" (read, "non-engineers") building and operating submersibles initially struck me as Darwin Award material. [hanging head] Sorry ... I'm a product of my environment and training. ;-) In my defense, the thought of *personally* building a submersible struck me similarly. However, although some members' suggestions and designs still scare the &^%* out me, by and large the design approach generally used (read, "*large* safety margins, redundancy, moderate operating ranges, and KISS") has alleviated most of those concerns. So much so that I've begun the design process for my own. I've yearned to see the true depths since I was a child watching my hero Jacques Cousteau on TV. I bought and read (and still have) a copy of Man Beneath the Sea (Penzias & Goodman) when I was in eighth grade (1976). Marine Biology would have been my next choice had I not pursued Computer Science & Mechanical Engineering (focuses in alternative fuel use and robotics, respectively). Ironically, it wasn't until running across this group that I remembered a passion that had gotten misplaced somewhere along the path of my life. However, as a diver, the thought of crossing the 160' threshold is still not comfortable for me personally ... the result of a catastrophic failure (the bane of engineers) is not an acceptable risk to me. Nor would I be able to adequately justify it to my wife & best friend of more than twenty years.
As a result, I've chosen to build in the middle-ground ... a "Scalable, Modular Single-Person 1-Atmosphere Hydrobatic Multi-Purpose Platform". I'm basically designing a superstructure for extended dive range & duration within the 0'-160' range and a crush depth of at least 320'. A fully-supported bale-out at 160' I can justify, both to myself and to my wife. As a hydrobatic, speed and maneuverability (AKA hydrodynamics) are primary design requirements ... and appeal. Truthfully, I'm largely soothing my "depth inadequacies" by making it as *fun* to operate as I can. Too bad I *hate* fluid dynamics ... but I'll get over it. :) The "scalable" and "modular" aspects simply mean that the final design must be alterable for greater depths simply by scaling the hull thickness and replacing the scuba-based equipment with equivalent rebreather-based components. Mission-specific equipment (additional air & batteries, cameras, sensor packages, manipulators, salvage lifts, etc.) are enclosed within readily-exchangeable, hydrodynamic, external pods that contain integral buoyancy chambers that integrate with the primary ballast system. Coming full circle to the origin of the thread, my current design uses the primary thrusters and hydrofoils for surface propulsion. A fledgling side design involves surfacing and mating with a catamaran-/trimaran-like support structure.
Choosing an initially shallower operating depth range also means that I have a broader range of acceptably safe hull materials and components to choose from and that the final design *should* be more within the range of the average homebuilder both in terms of cost and required construction skills. Although my intent is not to pursue it commercially, I could easily see it satisfying cost-effective niche market solutions within the sport/leisure, cinematography, research and salvage fields. The fully-modular design approach means that the same superstructure can be used without modification over a broad range of applications, missions and budgets, and be easily "upgradeable".
In closing, and before returning to Lurk-Mode, I just wanted to say thanks for the inspiration!
Warm Regards,
Shawn