# 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: Doug Royer
Date: 2005 Feb 2, 10:54 -0800

```Doug

Not clear what the old and new displacements are relative to a a couple of
counts.

How many pounds in a ton for this formula (I am assuming with displacement
we are not talking gross or net tonnage as a factor of square feet of cargo
capacity)?

a.  Is there a baseline displacement based on the displacement of an empty
vessel plus fuel etc?  which is already factored in before we add or
subtract cargo, or

As I understand it(I'm no mathematician)these formuli are based on ratio.As
long as the units are kept squared away in each formula answers will give
the needed info.
That said these are the basic formuli.You manipulate them as needed.There
are other steps or mutations of these formuli one adds or not(as in reguards
to auxillary usage)as needed.There are also others that I didn't include.
In real life the bridge or chartroom has volumes of gragh/plot books used
for easy,speedy referance for the baseline info(such as rpm to speed or fuel
consuption at a certain speed/g.t. weight).

b.  Is the new displacement the total weight of the ship, fuel, cargo etc
plus/minus the added or subtracted cargo?

It is usually gross tonnage for all calculations. We know what the un-laden
tonnage of the vessel is so by adding/subtracting the weights of
cargo,consumables(fuel,fresh water etc)as they are loaded,discharged or
consummed you have the displacement.The set-up of the data for some of this
can get complex and time consumming.

Tangentially, in practice does a captain run close to hull speed (assuming a
non-perishable cargo and sea conditions permitting) to save time, or back
off to decrease fuel cost?

Put another way, is the earning capacity of the vessel per day so large that
fuel cost be damned, only time is money; or is the margin slim enough that
he has to calculate the cost/benefit ratio of speed (time is money) vs. fuel
(oil is money)?

This seems like an easy question but really isn't.There's so many
variables(such as safety).I will say that time seems to be the over riding
factor.These cargos are consigned to be picked up/delivered at specific
cargos at multiple ports along the baseline track.For example: scheduleing
has the vessel in say San Pedro to pick up 3,200 tons of containers at warf
B on 02-13-04 starting at 1300 hrs.At 1900 hrs it has to be at warf G to
load 500 tons of frozen beef.The vessel is scheduled to leave S.P. by 0845
02-14-04.Offloading the 500 tons of beef at the Port of Ventura by no later
than 1600 hrs 02-14-04 and be underway to offload the 3,200 tons of
containers at Warf 23 in S.F. by 1300 hrs 02-15-04 etc.
I'd say time is the most important factor.
The earning capacity of these vessels are enormous!
It would stagger you the amounts of capital moved and made by just 1 vessel
during a transit.The company I used to work for had a fleet of 17 vessels.

```
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