Peter,

  Prior discussions of planing and hull speed aside, this particular discussion makes sense. 

  The force measurement of newtons came from Rick, and was a means of stating what thrust the motors would have to produce to move the 18m proa at 4 m/s in ideal (theoretical) conditions.

  Force times distance equals energy.  Force times distance, per second, equals power, or energy exerted per second. 

  Rick did the calculation from newtons to horsepower in post 1068 (at 2:55 am GMT, I think).

        - Mike

 

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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