[Sca-cooks] OT-knots and medieval boats

[Decker, Terry D.]

A very nice exposition, Brandu.  Please allow me to add a few comments.

> > Okay, landlubber question. Exactly what is the "49 tonne"
> referring to
> > here? Weight of the vessel? Displacement? Maybe those two
> are the same?
> > Or the wieght of the cargo it can carry? What does that work out to
> > in size measurments? (other than rather small, although you did say
> > "coaster").
>
> OK, here goes:
> In period, as a general rule, ships were rated by the amount
> of cargo they
> could carry, this was not measured in weight, but in the number of tun
> barrels of liquid she could carry. The Tun was generally 252 gallons,
> usually, though the Spanish tun varied rather a lot, and
> could be as little
> as 125 gallons- which made any Spanish estimate of the size
> of ships rather
> suspect.

"Tun barrel" is redundant.  By definition, a "tun" is a barrel to hold
liquids and appears in Old English as "tonne."  There are related words in
the various languages over the Celtic range, so it is believed the origin
may be Celtic (defined in this context as a group of related cultures and
languages spread from Asia Minor to Ireland).

The tun of 252 U.S. gallons (the same as the Elizabethean wine gallon) is an
English measure of approximately 2 butts or 4 hogsheads or 8 barrels
(Elizabethean wine measure).

The Danish "tonde" is about 139 liters, which makes it roughly equivalent to
the English wine barrel (119.24 liters).  It is related to one of the
meanings of the German "Tonne" meaning "barrel" (a usage for which I have
been unable to determine any specific measure).

The "tonelada" is a traditional Spanish and Portuguese weight measure
standardized from their "tuns."  The Spanish "tonelada" is 2000 Spanish
"libras" (about 919.9 kg).  The Portuguese "tonelada" is 1728 Portuguese
"libras" or "arratels" (about 793.15 kg).  Variations between Spanish,
Portuguese, Genoese (there were several colonies in Spain and engaged in
trade) and Moorish measures may be part of the problem with the wide
variation in Spanish measures of the period.  A number of Spanish measures
(especially land measures) were standardized in 1568, but the old measures
continued to be used.

>
> This should not be confused with the modern measurement of
> Tons, which is
> actually the weight of water she would displace, when full.
> As any student
> of Archimedes will tell you, this also happens to correspond
> to the total
> weight of the ship, crew cargo and supplies.

Tons displacement is commonly used to measure warships, although it is
sometimes on other craft ("register tons" are more common for merchant ships
covered a little later).  A ton of sea water is about 35 cubic feet, so
every 35 cubic feet of water a ship displaces is a ton displacement.

Although there is no real correspondence, the English "tun" is about 33.7
cubic feet.

>
> This was one common period measure of ships capacity, another
> is the number
> of "Chaldrons" of Coal, Bales of cloth, or bushels of grain she could
> carry. All were used rather interchangeably, and all referred
> to the only
> measurement that really mattered to a merchant seaman, how
> much bulk cargo
> could she carry.

"Chaldrons" (AKA chalder or cauldron) are worth a look.  Deriving from the
French for "large kettle," it is an English measure for dry commodities
(coal, lime, etc.) standardized at 36 bushels.  More modernly, as a measure
for coal, a chaldron is 1/8 keel (a keel being 21.5 metric tons and
approximately the cargo capacity of a Tyne river barge in 1695).

Bales of different goods produce different measures.  A bale of paper is ten
reams.  A bale of cotton is 500 US pounds or (Egyptian cotton bale) 720
British pounds (down from an original 750 pounds).

>
> "Tonnage" was actually an estimate - based not on actual
> usage, but on the
> ships dimensions, according to a formula recorded by Master
> Matthew Baker,
> a famous ( perhaps the most famous ) Elizabethan shipwright.
> The formula used by Baker is recorded as : (LOA x W x D)/100
> ( - length
> overall (in feet) x maximum width (in feet) x total depth of
> hull(feet)
> divided by 100 )
>
> Because it required nothing more than the gross overall dimensions,
> measurement in Tonnes became the generally accepted standard,
> and the other
> measurements are infrequently used, except the Chaldron.
>
> Brandu/Elias

These are usually referred to as "register tons" because this is the method
used to gauge ship capacities in most ship registries.  A register (or
merchant marine) ton is 100 cubic feet.

If you come across any information on standardization of any of these
measurements, please let me know.  I'm trying to chase down some of the
history to clarify precisely when some of these changes occurred.

Bear