What floats your boat.

Tom, you seem like a nice enough chap and I have to hand it to you, you have singlehandedly stirred the sleepy halls of BoatDesignNet and will probably end up with a thread that will have 90k hits by the end. And here I am still suckered in after I said I was done. I'm just a rube and you've engaged the heavy hitters; go figure. I swear I'll try and make this my last comment but do you realize that that last drawing is meaningless? Why not just throw a duck and hippo in there to make it complete?

 

As you say you increase surface area, great, so total water buoyancy force pressure pushes in all directions.


We do not want constant mass and beam with our boat design but a boat that suits our customer requirements.

 

Updated that pic for you Tom.

Note that the submerged areas (number of pixels) is actually approximately to scale (and where it isn't perfect I've erred in your favour).

As you can see, adding a V to a flat bottom, with constant mass, increases draft.

Buoyancy is the force component from the pressure that pushes up.

That is neither here nor there. You started all this with this statement:

 

It gets to us all, if I took the advice from many people trying to sell me something with out researching I would not now be debt free and happily retired for many years. I like observable results.
I am using the information supplied at teachengineering.org can you suggest a more reliable source of information.

 

A more reliable source of information would be an introduction to naval architecture text.

 

Buoyancy pressure like atmospheric pressure pushes in all directions.
The boat we are planning to building has it`s own mass and is most relevant
to our design. Add more buoyancy you get more uplift from the water acting on that surface. I hope that is true or I would not have much use for a life jacket.
Saying " that is neither here or there " is not much help to anyone.

 

And where do we get that information for free like the INTERNET.

You would pay big money and just get the information that suited the NA`s
competence. Probably.
It is very likely a NA would not discuss a controversial subject for fear of getting it wrong in front of his mates, similar to the foil, wing debate.

 

No Tom, pressure is omni-directional, buoyancy refers only to an upwards direction.

A V only adds more "potential buoyancy" - i.e. if the boat was a sealed unit, then when completely submerged the V bottom boat would have more buoyancy.

But when floating, the same, perfect amount of buoyancy is always used (const mass), so when you go from flat to V you just change where the buoyancy is generated. You lose some up high at the outside, but gain some lower down in the middle.

It's not in the least bit controversial!
This is simple, basic stuff.

I'm an NA discussing it with you in front of my "mates", there's nothing to fear.

Have a look at some of these:
http://mysite.du.edu/~jcalvert/tech/fluids/hydstat.htm
https://phet.colorado.edu/en/simulation/buoyancy
http://ocw.usu.edu/Civil_and_Environmental_Engineering/Fluid_Mechanics/CEE3500_L5_Statics2.pdf
https://www.khanacademy.org/test-prep/mcat/physical-processes/fluids-at-rest/v/fluids-part-5

 

A vector integration.

The mathematical relationships here must consider not just area, but the vector relationships that give a component in the same direction as the gravity vector. This problem is clearly a classic vector integration problem.

Just stating that submerged surface area as the relevant parameter here is misleading. As indicated earlier, the integrated area X local liquid pressure X the component opposing gravity (cosine of the normal vector for the plane element with respect to the gravity vector) gives the bouyant force, and yes, it is always equal to the weight of liquid displaced.

Within the constraints of this fundamental equation, one can imagine a flat bottom hull having more or less draft than a v bottom for the same displacement. Within the constraints of this fundamental equation, one can imagine a hull with greater or lesser submerged surface area for the same displacement.

Adding constraints, one can generalize that a v type botton will usually have a deeper draft, but that conclusion is not assured by the fundamentals of the bouyancy principles.

 

Hmm..i loath to wade in, but.....The reason why you “don’t get it”, is because that fig.1 in that website is omitting the most important aspect of the “lecture”. Below is a modified but fully correct version of what should be posted.



Take your solid block of wood, let’s call is anything except wood (to avoid confusion with materials), just call it a solid that is now fully immersed in water as shown.

The pressure on the lower surface, B, at a depth of h2 is greater than the pressure on the upper surface A at h1.

The pressure on surface D and C also act as shown, perpendicular to the surface.

Simple physics tells you Force = pressure x area.

So, for surface C the force = pressure x area, and since both these surfaces are same size same depth the area and pressure is the same, ergo so is the force.

Now, not forgetting the vector of the forces on surfaces A, B C and D must be added together. But by inspection the force on surface D = force on surface C, but opposite direction, therefore these cancel out.

So the upward force on surface B = press x area. And we all know pressure is simply (rho)gh.
Rho is water density, g = 9.81m/s^2 and h = the water depth or head. So h is h1 and h2 for surface A and B respectively. And let’s call the area of each surface A.

So this can now be rewritten as resultant force vertically = Force on surface B – force on surface A.

= (h2 – h1).(rho)gA

But we know that (h2-h1)A = volume of the solid, let’s call it V.
(since the upthrust is equal to the weight of the fluid displaced by the object).

Therefore upthrust = V(rho)g = mg.
Where m = V.(rho).

QED Upthrust = weight of liquid displaced.

 

Thank`s for that information it will take me a while to follow that through.
I do not think I am game to tell my customer that he can not have his v bottom and still have a shallow water boat. He will probably tell me there would only be a very insignificant difference anyway in draft and to go ahead with the improved design he asked for so he can have the advantages of a shallow v bottom.

Archimedes`s empirical observation is interesting, but as an explanation for how something floats it is very limited. It tells us that something has to happen,but it doesn`t
give us a mechanism that explains why that happens.In order to really understand what is going on with buoyancy, It is necessary to understand the idea of water pressure.

 

On the contrary, assuming constant mass, max beam, LWL, etc it isn't possible for a V bottom to not have a deeper draft.

 

Tom, do you really have an actual customer for a boat design other than yourself? If so please respond yes. Otherwise please drop the pretense of having a customer.

 

And what Ad Hoc has shown above can be generalized to an object of any shape. Buoyancy, aka upthrust, of a floating object = weight of the fluid displaced by the object, independent of the shape of the object.

 

Who is claiming that a boat with a shallow V bottom can not be a shallow water boat?