Spill Plates and general aerodynamics.

[Dave Cofone]

Bernoulli theory is ideal flow in a incompressible fluid without friction thus no boundary layer which is a major part lift analysis. The inclusion of friction and fluid air deflection needs to be included as discussed below:

http://hyperphysics.phy-astr.gsu.edu...s/airfoil.html

http://www.aviation-history.com/theory/lift.htm

It seems we have a difference of opinion. This is a good thing and so are the articles you have posted. Lots of learning going on which can only be a good thing. I love a spirited debate because I always learn something.

Yes we do. To really understand lift study what happens with lift generated on a symmetrical curved surface like a thin sheet of fabric on a sail boat. The sail, if trimmed right is curved smooth with no ripples, generates lift when tacking into the wind in the horizontal direction and the forward part of that lift force causes the sailboat to go tacking into the wind. This lift is the air deflection part from circulation theory. Same thing happens with a wing on a plane.

[Dave Cofone]

I get what your argument is.....and you are 100% correct about the Magnus effect and I stand corrected on that point. However you explanation of the sail on a sailboat falls down for two reasons. First the very reason for tell tail windows cut into the sail is be able to see if there is flow on the backside of the sail. If the tell tail is not streaming straight back then airflow has broken away from the sail (wing). This is where the jib comes in to help keep the airflow stick to the low pressure side of the sail. Second, ridgid wing sails (actual wings) that are now popular on America's Cup boats are completely symmetrical and way more efficient than fabric sails. Very little deflection lift here and a ton of speed especially on a direct beam reach........

[baries]

I've read with interest the articles posted and yes some good information has been shared, but no one has said much about the design of the euro PRO boats with speeds in excess of 100 mph and not a fence in sight, imagine that.

[Ram4x4]

Different hull design.

[KURPS]

Different hull design. Explain please!
Both are hydros, one is fast the other not so fast.

[Ram4x4]

Look at one compared to what we drive. Much longer, lay down, different weight distribution. As for speed, they have jacks they can raise and lower the motor while driving, etc.

To be honest, I've thought having wind fences on our boats would tend to make the front want to windmill around once moving (like tossing an arrow backwards), but some say taking them off has adverse effects on handling. I don't have an explanation, aerodynamically speaking, as to why that would be other than no fences is allowing air to spill off the sides which is causing some kind of adverse yawing. But, there are some designs that have little or hardly any fence at all, soooo...