What floats your boat.

No wonder the Titanic sank, not enough surface area !

 

This statement is wrong. Who ever wrote it either did not understand the fundamentals of buoyancy, or forgot to include that the "cosine" effect discussed in post #29 of this thread.

A simple thought experiment: What is the buoyancy of a thin piece of sheet metal with thickness 0.001m and width 1m suspended vertically in water to a depth of 1m? The submerged steel weighs 78.4kN/m^3 * 1m * 1m * 0.001m = 0.0784kN

Based on the statement above it would be 9.8kN/m^3 * {(2* 0.5m * 1m * 1m) + (2* 0.5m * 1m * 0.001m) + (1m * 1m * 0.001m)} = 9.8196 kN and the steel would float.

Based on the principles in post #29 or on Archimedes Principle it would be 9.8kN/m^3 * 1m * 1m * 0.001m = .0098kN and the steel would not float.

 

The reader must be getting bored with this stalled discussion. It needs an injection of illuminati reptilians from Area 51 to raise the interest level.

 

Can I ask why you just don't state the weight of the steel but give a formula?

 

The way DCockey did it is better. Otherwise a good logical argument can be made on one false premise that goes unnoticed.

 

Right, well everyone is agreed, down is really up, OK ?

 

Starting with the last line, you are quite correct. The objects drawn are all just floating. Technically all the objects in the sketches are flat bottomed but do not have the same draft.

Areas in contact with the water for a unit length.

A: base 8x1 sides 2x2x1 front back 2x2x8 total 44
B: base 4x1 sides 2x4x1 front back 2x4x4 total 44
C: base 2x1 sides 2x8x1 front back 2x8x2 total 50

A and B have the same contact area and different depths
C has most contact area but is actually the deepest

As a general principle the site is wrong

Had they said for a rectangular block the one with the greatest plan area has the least draft I would agree.

 

No Tom, no. Reality and the laws of physics as we know them say otherwise.

This is a poorly written sentence, and evidently misleading.

The cube of wood does float, as does the plank.

They both displace 50 lb of water, which obviously will be the same volume of water in each case.

The plank has a larger horizontal plane than the cube, so it doesn't need to sink very far into the water before the water pressure is high enough to hold it up.

The cube has less horizontal area, so it needs to sink deeper before the water pressure is enough to hold it up.

Just to be clear, FYI, you absolutely cannot make a cube that sinks into a plank that floats. Not possible.

Something you may have overlooked is that if you added a V bottom onto a previously flat bottomed boat (without changing mass), the waterline beam will not remain constant - it will decrease (assuming the flat bottom draft was effectively zero).

I.e. the V will have less horizontal plane (like the cube), because/so the V sits deeper where water pressure is higher, to maintain the same displaced volume as per Archimedes.

You are wrong Tom, give it up, this is getting silly.

Yes. Burn that into your brain.
It ALWAYS displaces the volume of water with mass the same as its own.

So if you change the boat shape, but not the mass, it still has the same mass, and still displaces the same amount of water.

So if you go from flat to V, the draft cannot remain constant, because if it did the volume of water displaced would change, which is impossible (because boat mass is constant).

This is only referring to the difference displaced by the clay of it floats, compared to the amount displaced if it sinks.
If it floats the displacement is always the same, and is independent of shape.

This point is something new from you, and not what we've been discussing up til now.

 

People have been trying to explain your misunderstanding of the grade school text book you are referencing in many different ways. Try this as a thought experiment; That block of clay
will sink either as a cube or flattened out as a thin pancake. It will only float when it is shaped into a bowl. A flat bottomed bowl will float higher and have less draft than a round or veed bottom bowl of the same diameter. What have you got to loose? Get 2 identical blocks of clay and see if your claim the greater area of the round bottom one will have less draft. No cheating, the bowls have to be of the same diameter. It is a no brainer
I hope, that a larger diameter bowl made from that block of clay will float higher.

 

Has the thread op been altered? I see no "claims have been made on this thread on certain subjects", but the first replies seem to indicate controversial claims were made .?.? Were they edited out?

Regardless,

He talks 'weight', he says nothing about shape or area.

 

If you read the thread False bottom v on a flat bottom, to where Tom Kane starts this thread, things will be in context. Tom states repeatedly a round or vee bottom will draw less water...

 

and yes the teachengineering text quoted here is utter nonsense.

 

You have all not read the requirements of the customer.
We need a boat that has as good or better possible draft as the boat in the image and built of wood. No bottom shape is mentioned but as a v bottom will obviously improve the boat to the customer requirements we can continue.

 

What is quoted is what teachengineering text says.

 

That doesn't make it any less nonsensical. Surface area (obviously) doesn't define boyancy. If it did barnacles would be awesome addition to boat hulls and we could have FRACTION of draft by gluing sand paper to the bottom of the hull.