[MHml] horsepower

[Bill Gibbs]

Maybe it's easier to get proportionally bigger props on two smaller engines?

It seems that one bigger engine should weigh less.

Thanks for the Gold Coast ref.

I'm 2 feet shorter LOA, and 1/2 their light weight of 22k pounds, 1/3rd
their heavy weight.  We weigh 10,000 loaded.
I'd be looking at an outboard, not a diesel.  100-200 hp is more achievable.
I'm toying with a removable sled idea.

Bill

-----Original Message-----
From: multihulls-bounces at steamradio.com
[mailto:multihulls-bounces at steamradio.com] On Behalf Of Diane Selkirk
Sent: Wednesday, January 31, 2007 6:57 PM
To: Informed discussion of multihull issues
Subject: Re: [MHml] horsepower

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

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