# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Barrels was DR thread from Nov-Dec '04
From: Bill B
Date: 2005 Feb 1, 17:54 -0500

```Doug

Wow!

Regarding:

w = pld displacement
W = new displacement

Can you further expound on the meaning of the above?

Thanks

Bill

> Doug
>
> George posted a plausible explanation of the cube method, but I have not
> seen your posting on how a merchant marine would solve the problem.
>
> Any hope I will see another way to skin the cat from you?
>
> Bill
>
>
>
> Here you go:
>
> s = old speed
> S = new speed
> c = old consumption
> C = new consuption
> w = pld displacement
> W = new displacement
> r = rpm at s
> R = rpm at S
> Ve = calculated speed by rpm
> Vo = observed speed
> De = calculated distance by rpm
> Do = observed distance
>
> Slip
> - slip = vessel speed outruns screw speed
> + slip = screw speed outruns vessel speed
>
> by speed
> % slip = ((Ve - Vo)/Ve) x 100
> by distance
> % slip = ((Do - De)/De) x 100
>
> Fuel Consumption
>
> by displacement
> log C = (log c + 2/3 log W)- 2/3 log c
> by speed
> C =(c x S cubed)/s cubed
>
> Speed by RPM
> speed in Kts = (60 x rpm x pitch x (1 - % slip))/6080
> rpm at given speed
> rpm = 6080/((pitch/1 + % slip) x 60) x speed in Kts
> rpm needed for new speed
> rpm = (r x S)/s

```
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