Hi John,
You might want to start with one of these.
http://www.propguardmarine.com/how.html
Despite their marketing claims, I haven't seen any independent research that backs up their data. However, even using their data, they show an increase in thrust, but no significant increase in speed. I thought that it was interesting that they state "Higher cruising speed at medium motor RPM. (with resulting fuel savings)" is a benefit, but the data shows only a 4% increase in speed at 2200rpm (on a 230hp outboard) to less than 2% at 2400rpm and back up to 3.7% at 2600rpm, and a slight decrease in speed at 3200. To me, that type of inconsistant data means that the "increases" may largely reside within the error range of the experiment.
The big benefit seems to be safety and all of the other companies that make similar products, like the thin stainless one that you suggested, sell them as prop guards. You can find a number of them witha simple search.
So you can skip the fabrication and move straight to the testing and data collection phase. Let us know how it works out.
Fair winds,
Eric
--- In electricboats@yahoogroups.com, "John Green" <v_2jgree@...> wrote:
>
>
> Hi there again Eric,
> I dunno about building a few winglet prototypes.
> Like my past idea for making lead acid batteries, I was throwing the
> idea out so that others can work on it, not me!
> I am a talker rather than doer...
>
> So, has anyone tried ducting a prop using thin sheet stainless for low
> wetted drag, and together with the duct, having static blades (that
> support the duct tube?) to lessen the column of water from rotating?
> Maybe Kort has! I should have looked that up before posting.
> This has probably never been looked at by ICE designers, as it is easier
> and cheaper to just increase the engine power.
> I have just taken a quick look at the Kort idea, and the drag of the
> duct might well be a factor, due to the airfoil shape of the duct
> itself. As most electric applications are probably for sailboats, the
> penalty of drag increase is greater, unless it can be lifted clear when
> not in use....
>
> John
>
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