[MHml] Friction Reduction

[Tom Speer]

Gary Pearce wrote:

>http://www.newscientisttech.com/article.ns?id=mg18925391.600&print=true
>
>I am not aware of it being tried on multihulls or indeed of any scientific 
>results other than the article above
>  
>
There's lots of literature on this.  For starters, take a look at:

Truong, V.-T., "Drag Reduction Technologies 
<http://www.dsto.defence.gov.au/publications/2398/DSTO-GD-0290.pdf>," 
Defense Science and Technology Organization, DSTO-GD-0290, 
http://www.dsto.defence.gov.au/publications/2398/DSTO-GD-0290.pdf

DK Group, "Air cavity ships are ready for a wider market 
<http://docs.hydrofoils.org/SAS03.pdf>", 
http://docs.hydrofoils.org/SAS03.pdf

Kodama, et al, "Microbubbles: Drag Reduction and Applicability to Ships 
<http://newton.nap.edu/books/NI000511/html/2.html>," 24th Symposium on 
Naval Hydrodynamics, Fukuoka, Japan, 8 to 12 July 2002, National 
Academies Press, http://newton.nap.edu/books/NI000511/html/2.html

A key question, though is, "Is the power required to pump the air 
through the injectors or slots less than the power saved through 
reducing skin friction of the hull?" It's not enough to reduce drag, 
there has to be a net reduction in power for the technique to be 
worthwhile. Otherwise, you'd be better off sending the power to the prop 
instead of the air pumps.

And that brings up issues like what volume of air is required to get a 
given llocal drag reduction, how long do the bubbles or air cavity 
persist before the air is swept away from the surface, will the 
technique work on a vertical wall as opposed to a flat bottom, etc. All 
of which are aimed at getting the most out of the amount of air injected.

I like Kodama's assessment, "Microbubbles can be called 'a big child -- 
immature, but with a bright future.'"

Cheers,

Tom Speer