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Old 02-22-2020, 08:03 AM   #1
Agemegos
 
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Default Cargo capacity of a 260-ton schooner

Suppose that a schooner of 260 tonnes displacement {34 m long at the waterline and 44 m overall length, with a beam of 8.3 m and a (maximum safe) draught of 5 m} were being used to carry cargo that was unusually dense not bullion bars, but dense enough that load was the limiting factor and tonnage was not a binding constraint.

How many tonnes (mass) could such a ship carry safely?
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Old 02-22-2020, 11:54 AM   #2
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Default Re: Cargo capacity of a 260-ton schooner

This may he of help, I'm on my way to work and haven't time to go over the maths just now.
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Old 02-22-2020, 01:54 PM   #3
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Default Re: Cargo capacity of a 260-ton schooner

Do we know the unladen draught of the vessel?
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Old 02-22-2020, 03:54 PM   #4
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Default Re: Cargo capacity of a 260-ton schooner

Quote:
Originally Posted by RogerBW View Post
Do we know the unladen draught of the vessel?
It would be of great help if we did.
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Old 02-22-2020, 04:55 PM   #5
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Default Re: Cargo capacity of a 260-ton schooner

Is that 260 tonnes fully stored or do you also need to reckon for stores?
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Old 02-22-2020, 04:58 PM   #6
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Default Re: Cargo capacity of a 260-ton schooner

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Originally Posted by The Colonel View Post
Is that 260 tonnes fully stored or do you also need to reckon for stores?
I don't know. It's just listed as "displacement: 258 tons", and indeed I'm starting to wonder whether that is displacement or burthen. It doesn't seem like much for a vessel that size.

Type: Schooner
Displacement: 258 t (284 short tons)
Length:
43.6 m (143 ft 1 in) o/a
34.1 m (111 ft 11 in) lwl
Beam: 8.2 m (26 ft 11 in)
Height: 38.4 m (126 ft 0 in)
Draught: 4.85 m (15 ft 11 in)
Propulsion: Sails
Mainmast, height from deck 38.4 m (126 ft 0 in)
Foremast, height from deck 31.3 m (102 ft 8 in)
Sail area 930 m2 (10,000 sq ft)
Mainsail area 386 m2 (4,150 sq ft)
Crew: 20
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Last edited by Agemegos; 02-22-2020 at 05:03 PM.
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Old 02-22-2020, 06:58 PM   #7
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Default Re: Cargo capacity of a 260-ton schooner

Quote:
Originally Posted by Agemegos View Post
I don't know. It's just listed as "displacement: 258 tons", and indeed I'm starting to wonder whether that is displacement or burthen. It doesn't seem like much for a vessel that size.
I'm guessing if it's a lightweight sailing boat it might have a really low displacement - I guess you've already seen the Wikipedia page on Displacement with all the different types with reference to storing.

Might this help?:
http://www.kastenmarine.com/cargo_yacht_120.htm
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Old 02-22-2020, 08:24 PM   #8
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Default Re: Cargo capacity of a 260-ton schooner

Quote:
Originally Posted by The Colonel View Post
I'm guessing if it's a lightweight sailing boat it might have a really low displacement - I guess you've already seen the Wikipedia page on Displacement with all the different types with reference to storing.
A vessel's displacement of course varies with how much stuff you load the hull with: it amounts basically to the total mass supported by the buoyancy of the submerged hull. In terms of the different conditions of loading defined in that Wikipedia article, I suppose that what i want is the difference between "loaded displacement" and "normal displacement" (or maybe "light displacement, though that would involve me in having to estimate the mass of the passengers, crew, and stores.
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Old Yesterday, 03:34 AM   #9
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Default Re: Cargo capacity of a 260-ton schooner

A back-of-envelope calculation:

34m 8m ⅔ to allow for hull shape = 180m area at water surface.

Assuming fresh water that's 180 tonnes per metre of draught change. (In salt water it'll be more.)
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Old Yesterday, 04:49 AM   #10
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Default Re: Cargo capacity of a 260-ton schooner

Yeah, but 34 8 5 = 1360, and 258/1360 is only 0.19, which implies very aggressive raking below the water-line. In fact, it's so small that it makes me worry. Deep narrow keel?

I understand a little bit about hydrodynamics, but I know very little about boats and ships. I simply don't know what might be reasonable to suppose about the difference between such a sloop's laden and unladen draught.
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