Forces on sailboats (#3)

They are not pointless, that is not correct. However, they are theoretical approximations and predictions, not actual measured values as the OP is asking for.

 

Oftentimes, the "actual measured data" is more chaotic though, and requires additional curve-fitting and smoothing to make sense of, making it hard to claim it is better than the theory.

Here's some Tornado catamaran predictions & measurements (from Bradfield).

 

You don't win races with curve-fitting, but with higher speeds.

 

That is not quite correct. He does not win the fastest but the one who arrives first.

 

Thanks so much for researching the question, I suspect it has raised some red flags with you as well?
I don't want to appear churlish, but I suspect these are also computer generated, not experimental data.
If they are experimental, I wonder how they got the boat heeling (at, e.g. 20°)? a) from the wind on the sails or b) being mechanically heeled in a test tank?
I would love to read the test report.
[EDIT] Thinking about it further, I wonder if they were just examining the hull's profile resistance at different heel angles, leaving out any consideration of the effect of the water flow at leeway angle over the keel?

 

Can you link or share that paper? It would make fascinating reading.

 

The data were obtained under sail (somehow). I'm attaching a pdf of the paper, which dates from the 1950's or earlier. The 6-Meter testing is described starting on page 11 of the pdf.

 

Brilliant, thanks.
My inquiry was answered on P453:

"Usual methods" covers a multitude of sins!

 

I found this in Fossati:


According to this diagram, whilst the Lift increases both with speed and leeway angle, λ, Resistance only increases with speed.
For example, irrespective of the leeway angle, at 2.5 m/s (~5 kts), the Resistance is ~300N whether the leeway angle is 0.25° or 3°, implying there's no increase in drag to increase the lift from ~10N to ~2,000N : a L/D ratio of infinity (1/0).
I don't think that's right at all. The keel does have a L/D ratio which be heavily influenced by the λ.
I'm looking for some reliable experimental results to establish the values.

 

I tend to think that we over think this a bit...recall earlier people ventured forth dumb and did not do so bad...but just me...a decent rig looks good and sails good...of course I admit to an earlier bend...Kid if it looks good, it is good,,,,

 

Yeah, I'm pretty much in the same camp, it's too easy to end up jousting at windmills, (or trying to screen out gnats with a picket fence).
That path leads to "Majoring in Minors".