Subject: RE: [harryproa] Re:: Flat Bottom Harryproa
From: "'Peter Southwood' peter.southwood@telkomsa.net [harryproa]"
Date: 3/26/2015, 2:18 AM
To: <harryproa@yahoogroups.com.au>
Reply-to:
harryproa@yahoogroups.com.au

 

Talador,

These are not my figures you are quoting, so I will not comment on their origin or accuracy, as I don’t remember the context.

However: A Newton is a unit of force, and a Watt is a unit of power.  You need to read up on the SI units before trying to calculate with them. Garbage in => garbage out. The internet is full of primers on imperial/metric conversion and basic physics and engineering primers. Wikipedia is usually reliable at this level.

Cheers,

Peter

 

From: harryproa@yahoogroups.com.au [mailto:harryproa@yahoogroups.com.au]
Sent: 25 March 2015 07:33 PM
To: harryproa@yahoogroups.com.au
Subject: [harryproa] Re:: Flat Bottom Harryproa

 

 

Peter - "Power is a function of speed times drag.  So 800N at 4m/s (say 8kts) equates to a power input of 3200W.  At 60% efficiency that becomes 5.3kW"

 

I have tried to convert that to hp, but I am totally confused. A Newton = a watt so 800 N = .8kW so where does the 3200W  (4.26 hp) come from? It seems low, even the 5.3 kW seems low.

 

And why are you using a 60% efficiency? I thought you said the Electrical/motor system was apx. 90% efficient?

 

Also these figures are for the boat not each individual hull? Correct?



Thanks in advance,

 

Talador

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Posted by: "Peter Southwood" <peter.southwood@telkomsa.net>
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