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Effect of weight on boat speed

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423zero View Drop Down
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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 6:08pm
https://www.britannica.com/video/181395/Discussion-forces-bodies-water#:~:text=When%20an%20object%20enters%20water,This%20is%20called%20displacement.
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Post Options Post Options   Quote epicfail Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 6:21pm
Maybe slightly off topic but.. We get some double handers doing handicap racing being sailed singlehanded - normally in light to moderate conditions. Assuming that the PY is based on these classes being sailed by two people - removing the weight of an average adult must have a significant impact on boat speed. 
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 6:23pm
The second paragraph is wrong for starters "The object pushes out a volume of water that is equal to its own volume." that is only true for an object that sinks. For an object to float it must displace less than it's volume of water.

They go on to qualify but it's all a bit 'lies to children'...


Edited by Sam.Spoons - 05 Nov 20 at 6:24pm
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 6:28pm
Originally posted by epicfail

Maybe slightly off topic but.. We get some double handers doing handicap racing being sailed singlehanded - normally in light to moderate conditions. Assuming that the PY is based on these classes being sailed by two people - removing the weight of an average adult must have a significant impact on boat speed. 

In the light it certainly does but so when the wind picks up the lighter 'crew' is at a disadvantage. I suspect that at clubs where such practice is common they will have a lower PN to apply when the helm is sailing alone. OTOH would it be fair to give a couple of 50kg teens the straight PN handicap while penalising a 100kg adult for sailing alone?
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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 6:33pm
https://en.m.wikipedia.org/wiki/Displacement_(fluid)
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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 6:42pm
https://en.m.wikipedia.org/wiki/Buoyancy
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 6:48pm
Yup, that's pretty much what I was saying.

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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 6:49pm
More specific to why ships float
https://letstalkscience.ca/educational-resources/stem-in-context/why-do-ships-float
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 6:58pm
That's wrong too..... It says 

How does buoyancy relate to density?

If a block of wood measuring one cubic centimeter (1 cm x 1 cm x 1 cm) is placed in a container of water, the amount of water displaced will equal the weight of the block of wood. But what about if a block of the same size is made of lead? Lead has a much higher density than wood. If a one cubic centimeter block of lead is placed in a container of water, the amount of water displaced will equal the weight of the block of lead.


The amount of water displaced by the block of lead (weighing 11.34g) will be exactly 1cc and will weigh 1g, so it will equal the volume of the block of lead but not it's weight  Wacko

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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 7:05pm
I think they mean, the amount of air (buoyancy) to weight of object, to make it float, ie you will need more air (buoyancy) for lead to float than wood.
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