flying fish wrote:David Wine
I read your article on building an efficient boat. I was curious about one thing I noticed in the article.
The "Blue OX" boat made 1650# of thrust with a 2.3 gear and a 82" 3 blade Maximus prop.
Also, on "The Fox" boat, a ZZ383 was used and the torque was at 420# compared to the 560ish pounds torque the ZZ502 produces. Both motors utilized a 2.3 ratio reduction. How can one anticipate to make 1600#'s thrust with a ZZ383 and the ZZ502 made 1650# thrust. Seems the same prop is being used except these chosen props rotated different directions.
I realize the prop being used is all that. I run the same design. The thing that I can't figure is a 420ft lb motor making within 50#'s thrust of a 560 ft lb motor.
In your article, you also noted that the ZZ383 produced only 50#'s less thrust than the ZZ502 with the same propellor design and near the exact same reduction ratio. Can you please further explain this??
Gar Toof wrote:
So by your formula my 220 should have a 62" propeller. I don't think that will work very well. Maybe I missed something?
I don't know what the HP at what RPM that your "220" is but the 10.61 HP per sq. ft. of disc area ratio is a design option for higher HP engines on trailer-able airboats. If we assume that the 220 is 220 HP and you have room in the cage for a larger prop, a lower ratio (say 6 to 8 HP per sq. ft. of disc area would be even better for developing pounds of thrust per HP. (The article stated that "in general, larger props are better" if there is room in the cage.)
Kindly go back to the article at the head of this thread and again read the paragraphs describing how the additional disc loading (HP per sq. ft. of disc area) of the Blue Ox setup (compared to the Fox setup) degraded the efficiency of the Ox's propeller's thrust results to find your answer.
Questions for plumcrazy, if you are listning:
Did you ever measure the thrust of the Fox after you bought it? At the time, we found it performed so well that we were not courious about its exact thrust number. Also our attention was more on the sound levels of this top performing airboat. Where is the Fox now? Does anybody know? Perhaps its current owner might want to test it?
Now speaking to the direction that this thread has taken: The caption of the article that it began with stated that the article was about a fuel efficient, quieter airboat. In the article I did not suggest that a builder of such an airboat go out and "find yourself a builder of top end, high RPM, high HP with attending initial cost, fuel burn and upkeep" engines with "big gear reduction units" for this plan. I suggested that one should seek an "off the shelf crate engine", use a 2.3/1 belt drive reduction unit and still expect top end performance.
Extra high HP engines are available from many engine builders and they are a part of "competitive" and "bragging rights" airboating. They are "lots of fun" if one wants and can afford them.
This article (and the resulting Fox airboat as a proof of the concept) describes a plan to produce a top performing four passenger "ride" airboat that will "be there before the crowd gets there", and get there quietly by focusing on "elegence of combined and complete design" rather than just horsepower.
I think that former President Harry Truman is quoted as saying something like "Its amazing how much you can get done if you don't care who gets the credit".
Some of the recent posts on this thread, while appreciated, are rather embarrassing, but thanks anyway.