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14-05-2009, 10:25 PM
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#1
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Registered User
Country: uk
Location: uk
Cruising area: southcoast
Join Date: Dec 2007
Location: uk
Posts: 528
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buoyancy
how do you work out how much buoyancy is needed to keep your boat afloat if it all went tits up?
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14-05-2009, 10:32 PM
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#2
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Traveling
Country: UK
Location: Alderholt
Occupation: Aerospace
Boat name: T/T D2S
Boat make: Midas 27' Cat, Argo 16 Cat. Avon Rib Thingy
Engines: Merc 280-ROS -JSRE,65Xs, 75 Stinger, Yam 60
Cruising area: Any Seedy Bar
Join Date: Sep 2004
Location: Alderholt
Posts: 4,225
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Hint:
What does the boat weigh
struggling as the words buoyancy, Tits & afloat all appeared in the same sentence
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It is impossible to lick your elbow.
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At least 75% of people who read this will try to lick their elbow!
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14-05-2009, 10:35 PM
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#3
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Registered User
Country: UK. Essex
Location: Mayland
Occupation: Train Driver
Boat name: Un-named as yet
Boat make: Phantom 21
Engines: yam 225
Cruising area: Thames estuary Black water/crouch
Join Date: Apr 2009
Location: Mayland
Posts: 373
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yeah see what you mean
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14-05-2009, 10:53 PM
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#4
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Registered User
Country: uk
Location: uk
Cruising area: southcoast
Join Date: Dec 2007
Location: uk
Posts: 528
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tits
it ways 2.5 tonnes,with no nipples
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14-05-2009, 10:58 PM
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#5
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Traveling
Country: UK
Location: Alderholt
Occupation: Aerospace
Boat name: T/T D2S
Boat make: Midas 27' Cat, Argo 16 Cat. Avon Rib Thingy
Engines: Merc 280-ROS -JSRE,65Xs, 75 Stinger, Yam 60
Cruising area: Any Seedy Bar
Join Date: Sep 2004
Location: Alderholt
Posts: 4,225
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 I'm now no help for a short while
__________________
It is impossible to lick your elbow.
Team25Racing.com
At least 75% of people who read this will try to lick their elbow!
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15-05-2009, 10:32 AM
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#6
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Registered User
Country: UK
Location: Windermere
Join Date: Oct 2005
Location: Windermere
Posts: 559
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I seem to remember 1 cubic meter of air displaces 1000kg, so 2.5 cubic meters ???
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15-05-2009, 12:08 PM
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#7
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Registered User
Country: UK. Essex
Location: Mayland
Occupation: Train Driver
Boat name: Un-named as yet
Boat make: Phantom 21
Engines: yam 225
Cruising area: Thames estuary Black water/crouch
Join Date: Apr 2009
Location: Mayland
Posts: 373
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with or without nipples
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16-05-2009, 01:04 PM
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#8
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Registered User
Country: England
Location: Cowes, Isle of Wight
Occupation: Marine engineer/electrician
Interests: Boat, Landy, and other toys :)
Boat name: Mad Max/Master Fiddler
Boat make: Phantom 18/Fletcher Bravo
Engines: Merc XR2
Cruising area: Solent/IOW
Join Date: Dec 2005
Location: Cowes, Isle of Wight
Posts: 935
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I seem to remember being told that you should have 1.5 times the weight of the boat. Therefore if the boat weighs 2.5 tonne you would want at least 3.75 tonne of buoyancy.
But that's just what I've heard...
I've got 2 tonne stuffed up in the bow of my P18 and I'm sure it'll keep the nose poking up if things got a bit "over-exciting"!
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Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, grinning from ear to ear, overdosing on adrenaline and proclaiming “KINNEL!! WHAT A RIDE!!”
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16-05-2009, 09:04 PM
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#9
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Registered User
Country: England
Location: Crayford, Kent.
Occupation: Electrical gezza!
Interests: Petrolhead
Boat name: Wayne Kerr
Boat make: Phantom xl
Engines: Mercury 2.5, 200(ish)
Cruising area: Essex, Hampshire, Mediterranean
Join Date: Sep 2004
Location: Crayford, Kent.
Posts: 1,199
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Quote:
Originally Posted by Maxim Gibson
I seem to remember being told that you should have 1.5 times the weight of the boat. Therefore if the boat weighs 2.5 tonne you would want at least 3.75 tonne of buoyancy.
But that's just what I've heard...
I've got 2 tonne stuffed up in the bow of my P18 and I'm sure it'll keep the nose poking up if things got a bit "over-exciting"!
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What have you got "2 Tonne" encapsulated in? 
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17-05-2009, 12:10 AM
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#10
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Registered User
Country: New Zealand
Location: Tauranga
Occupation: Boatbuilder
Boat make: Mitchell RecJet 48
Engines: Chevrolet LS364
Cruising area: rivers
Join Date: Dec 2007
Location: Tauranga
Posts: 36
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Although the boat may displace 2.5 tonne of water, it won't weigh 2.5 tonne when submersed. It has to do with relative density (ever wondered why that heavy stone is lighter in the pool rather than by the pool side?)
To be a little technical, fresh water has a density of 1 (it is the benchmark to which everything else is measured, hence 'relative density') anything with a relative density of less than 1 will float, anything with a relative density of greater than 1 will sink. This is why a boat floats, its overall relative density (including materials, load, and air volume) is less than 1.
With this in mind, you will need less than 2.5 cubic meters of air to keep the boat afloat once it is swamped.
As a side note, fuel (petrol) has a relative density of about 0.7, so therefore is a bouyancy aid in the event the boat sinks (of course it usually escapes and is displaced by water, so the aid is only tempory...
Fat also had a relative density of less than 1, that is why bigger people float more easily, and bigger tits float better than smaller ones!!!
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17-05-2009, 08:23 AM
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#11
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Registered User
Country: England
Location: Cowes, Isle of Wight
Occupation: Marine engineer/electrician
Interests: Boat, Landy, and other toys :)
Boat name: Mad Max/Master Fiddler
Boat make: Phantom 18/Fletcher Bravo
Engines: Merc XR2
Cruising area: Solent/IOW
Join Date: Dec 2005
Location: Cowes, Isle of Wight
Posts: 935
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Quote:
Originally Posted by Wayne Kerr
What have you got "2 Tonne" encapsulated in? |
Sorry I should've explained more, I have 4 large inflated sausages each rated to give 500kg of positive buoyancy....
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Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, grinning from ear to ear, overdosing on adrenaline and proclaiming “KINNEL!! WHAT A RIDE!!”
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