Aerodynamic question

[Shaunk]

Hi guys I'm new here and have a question which I hope someone will be able to answer for me.

Why is a canoe pointed at the front and the back if the ideal streamlined shape is rounded at the leading edge?

Does anyone have a scientific explanation for me? I feel it has something to do with reducing the skin friction as a rounded leading edge will have greater skin friction than a pointed one. I also think a rounded leading edge edge will create lift in the water which you dont need in a canoe.

Thanks guys
Shaun

[Raggi_Thor]

Originally Posted by Shaunk

...Why is a canoe pointed at the front and the back if the ideal streamlined shape is rounded at the leading edge?...

I am not so sure that is the simple case.
Why are cars these days more and more wedge shaped?

[KCook]

Easier to build, as you just run the keel up to the deck. Many small fishing boats do have a more rounded bow, but they are molded fiberglass. Besides, canoes need to LOOK like canoes.

Kelly Cook

[dennisolcott]

Pointy bows do better running into waves....which airplane wings don't encounter except maybe once.

[Raggi_Thor]

Maybe something like this?

[frosh]

The "Ideal" streamline shape with the rounded leading edge is for wings or foils that are designed to develop lift, especially at low and medium fluid velocities. Another instance of a rounded leading edge being preferable to a sharp one is if the direction of motion of the hull does not quite align with the fore-aft axis of the hull. Then less turbulence is produced on the lee side of the bow.
If the direction of motion is straight ahead ( motion and fore-aft axis are aligned), then a sharp bow creates a less turbulent wave therefore less drag, and is a faster bow shape.

[marshmat]

Frosh pretty much summed it up there.
Subsonic foils have a rounded leading edge because they need to operate at varying angles of attack. The rounded edge can be shaped to ensure ideal location of the stagnation point over a wide range of angles. A canoe hull needs to cut the waves, and generally only goes pretty close to straight ahead, at least in cases where speed/efficiency matter. So a sharper leading edge cuts the waves smoother, and also creates lower pressure drag and less wake (thus reducing the power needed to move the boat).

[vishnubaiju]

I feel three reasons for that.
1. The depth is less and has to cut the waves, so sharp forward is better, more speed also.
2. The design and construction is easier, only half the number of templates required.
3. The forward and reverse movements, especially when not powered, is easy when both the ends are sharp and similar.

[Shaunk]

Thank you everyone for your help.
I'm doing my batchelor of technology in Mechanical Engineering and had to research this topic.

cheers

[PATDave2]

Originally Posted by Raggi_Thor

Maybe something like this?

Thats a nice boat is that what you got? If it is what was the cost

[FranklinRatliff]

Originally Posted by Shaunk

Hi guys I'm new here and have a question which I hope someone will be able to answer for me.

Why is a canoe pointed at the front and the back if the ideal streamlined shape is rounded at the leading edge?

Does anyone have a scientific explanation for me? I feel it has something to do with reducing the skin friction as a rounded leading edge will have greater skin friction than a pointed one. I also think a rounded leading edge edge will create lift in the water which you dont need in a canoe.

Thanks guys
Shaun

Flowing water under a rounded shape can create a suction, pulling the bow down.

[Shaunk]

Originally Posted by FranklinRatliff

Flowing water under a rounded shape can create a suction, pulling the bow down.

As in a lift force. Just in this case the lift force will be pulling down as the LP will form underneath the vessel

[Poida]

Batchelor of Technology Mechanical Engineering I take it you haven't got to the bit where they teach you the difference between aerodynamics and hydrodynamics.

[FranklinRatliff]

Originally Posted by Poida

Batchelor of Technology Mechanical Engineering I take it you haven't got to the bit where they teach you the difference between aerodynamics and hydrodynamics.

Aerodynamics and hydrodynamics are subsets of fluid dynamics.

[SheetWise]

I recall reading a study done on submarines where it was shown that a rounded nose had less drag than a pointed nose -- I've also never seen a "sharp" bulb, which I would expect if it had less drag. I know I'm comparing under water to above water shapes -- but it doesn't follow that drag is a design consideration. Comments?