[MHml] horsepower

[Diane Selkirk]

Bill Gibbs wrote:
> How do I go about figuring out how much horsepower I need to push 
> Afterburner to 20+ knots?
> Transits would go by so much faster.  :-)
>  
> On a related topic, a friend has been lauding the extra efficiency of 
> dual motors as exceeding that of an equal combined HP single 
> outboard.  I hadn't heard this before.  Any opinions?
>  
> Bill
> Afterburner
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Lots.  I'd think (WAG) about 200-300 HP or so would do it.

Here's a Gold Coast cat http://www.goldcoastyachts.com/54ms.htm that has 
2 x 300 HP diesels to go 25 knots.  Your boat is likely a fair bit 
lighter and thinner but not by that much.

Your friend isn't correct.  Assume 2 x 100 HP or 1 x 200 HP engines.  
Each will drive a suitably optimized propeller.  Each propeller will 
have tip losses and drag due to the hub/shafting/outboard etc.  The 
bigger single prop will have less total drag and tip losses.  There's a 
reason the Gossamer human powered aircraft turned one big prop instead 
of 2 smaller ones.

Evan Gatehouse