Why a Yawl or Ketch instead of a sloop

[Paul B]

Originally Posted by Rick Willoughby

You are correct about the sheeting angles. The only way you will achieve this and have streamline flow is to push the camber further forward on the sail. You can do this with JavaFoil. It allows a higher angle of attack with each individual sail. The maximum camber occurs at more like 20 to 30% than the 40% of a NACA 4-series.

There is also the possibility of pushing the sail closer to stall (this is when you see the leeward tufts lift) and this could very well be the best sail trim for the best VMG. JavaFoil has various options to select for the stall condition but these are empirical relationships that are based on observations and not analytical in derivation.

Attached shows the leading foil with camber further forward that is still operating in streamline flow.

You can spend a long time modelling the exact shape of the sail to get it close to what is happening in real life. The aim would be to see what adjustments are made to then get better performance.

Rick W

Headsails do have the max camber closer to 30-35% than 40%.

This latest iteration of your foils would still be luffing.

I don't think I will ever understand what you are trying to show.

[Paul B]

Originally Posted by Milan

People as Greg Elliott? http://www.elliott-marine.com/primo.html

Next you will mention Mari Cha?

Specialty boats. In the 15 years since EM was launched, how many have followed?

Let's see how this boat would stack up against a TP52. Upwind there would be no contest.

[Ad Hoc]

Paul

Then perhaps ive missed the question/point you're asking?
sorry!

[Guest625101138]

Originally Posted by Paul B

Headsails do have the max camber closer to 30-35% than 40%.

This latest iteration of your foils would still be luffing.

I don't think I will ever understand what you are trying to show.

The apparent wind as experienced on the boat will be different to the true apparent wind as you experience aligned to the hull. These are caused by the leeway of the hull and the change in airflow around the sails.

To get the true angle of the wind you need to be removed from the infuence of the sails

Attached shows a foil of 1% thickness, with 10% camber located at 30% chord and an AR of 4. It is aligned to the position of maximum lift. You can see from the streamlines that the air has curved quite a lot as it enters the sail. This is not the true apparent wind.

The second image is the same sail but zoomed out to show that the flow is directly left to right.

The sheeting angle with respect to the apparent wind is about 15 degrees. The sheeting angle would be much greater for the wind angle approaching the front of the sail.

So the angles you experience depend on your frame of reference. There is no instrument using wind data around the boat that can give you the far field apparent wind. You would need to be collecting wind data from a fixed point and then adjusting to the actual velocity vectors to determine the far field apparent wind. All the angles I have shown above refer to the far field and this is taking undisturbed airflow directly left to right.

So sheeting angles with respect to apparent wind need to consider the frame of reference of the observer.

Rick W

[Boatpride]

Last week I sailed on board http://www.sailingnetworks.com/boats/view/2 in the photo she has four sails up. But we also used the Mizzen Stay Sail as well.

The sloop designs were quicker in light air. They are lighter and have longer keels. On the light air days we came in around the middle of the finishing order.

But on the two days when the winds were over twenty knots constantly we lead the field, being able to put up five sails and avoid broaching!

My money is on yawls!

[brian eiland]

I was just reviewing a few subject threads, and ran through all of this one real quick. There was much really good conversation here. I thought it desired reviving.