Greater Lift?

Greater lift will help pointing ability. Daggerboards also have less drag due to the fact that they don't have a centreboard slot on the underside of the boat creating more turbulence behind the board. Getting the bow down on the boat will also greatly help your pointing ability due to the hull generating a component of lift too, ie, the hull will be gripping water in a similar action to your foils.

I wasn’t sure that lift may be possible in fluids due to them being an almost incompressible medium, lift on a aerofoil is usually (non supersonic) created by having lower pressure above the wing than below as the air has to travel further over the curved upper surface and so speeds up and therefore reduces pressure.

 

In fluids is this possible? An area of cavitation (low or no pressure) could be created but these are usually associated with increased drag, which is not a good thing, so any lift type effect experienced was caused simply by creating a deflection on an angled surface moved through the fluid.

 

But I have since found this which appears to back up the lift principle;-

 

http://www.boat-links.com/foils.html

 

So I guess there may be a reason for the Hobie 16 after all!

Paul

Glad you mentioned Hydrofoils this is where I have a problem with the lift thing in water!

With danger of hijacking the original thread? Lift, as I understood, was the LOW pressure caused by an aerofoil section as the air has to accelerate over the longer upper surface SUCKING the aircraft into the air (this can even happen with the roofs of buildings). Agreed that there may be some increase in pressure under the section due to the angle the section is presented to the airflow (Angle of Attack, AOA) assisting this, however this is not lift.

Does a screw lift itself into a piece of wood as it is rotated? No the flutes of the screw cut at an AOA drawing the screw into the wood, does the propeller of a ship draw itself forward by lift, again no in a similar fashion to the wood screw it draws itself forward due to the AOA of its blades as they cut through the almost incompressible water.

If you were to place a flat section horizontally in water with the leading edge angled towards the surface, then the water was driven past it there would be an upwards force, which could be used to lift something like a boat, a hydrofoil?  But this upwards force was created in a similar fashion as the screw and propeller. I struggle to see this as lift as used in the aircraft model!

I don't think it's possible to distinguish between lift from an aerofoil shape and "lift" due to angle of attack.  For example, many aerobatic aircraft have completely symmetrical wing sections.  In order to get any lift it needs a positive angle attack but this doesn't change the fundamentals of what makes it go up compared to a non-symmetrical aerofoil.

Similarly, if you push an angled plank of wood through water (or air for that matter) the thing that makes it go up is the same: more pressure underneath the plank than above it.  It'll be high-drag and will stall easily, but I don't think there's a fundamental difference in what causes the lift.

Have a look at http://www.av8n.com/how/htm/airfoils.html#sec-thin-wings (scroll down to 3.10) for some information on using barn doors as wings.

Paul