sail aerodynamics

[schakel]

Originally Posted by yipster

i too am wondering about these flows, as a rig heels how much loss it makes, mast rake, and what if when battens or a top boom would twist more windward

If you use an outrigger for a stay running from the top of the mast to the boom at the side of the ship you have what you want because it will bent the mast windward and you make the upwash effect even worse because you bend it even more towards the sky and therefore create more downward momentum in the mast. On th other hand it is just a small part of the upwash since most wind leaves at the backend of the sail.

I heard these outrigger boom were forbiden in open 60.

[Paul Scott]

Schakel- I was trying to remember a piece by Bogotaj on sails where he points out that sweep and taper effect the amount of twist needed for a sail. Which seems to imply that more powered up twist (not luffing) equals more forward power, as the top of the sail is pointed more downwind than the bottom. Can you quantify how much power loss upwash causes?

Yipster, FWIW, Stradivarious, the new AC Tri, cants it's mast all over the place. If you haven't seen it yet, get on Youtube and search BMW Oracle Castleswreath. My wife and I video'd this, and it seemed to me that in addition to using cant to steer, they seemed to be playing with flow direction.
Some have speculated that mast rake is part of what makes windsurfers go so fast. A lot of classes allow a lot of rake- Contender comes to mind. I think I saw somewhere that the more rake made the boat faster.

Anyway, rake plus taper seems to equal more twist. And according to Bogotaj, fractional rigs too.

Paul

EDIT- I found the Bogotaj piece- 'How do sails work?' article by Paul Bogotaj. My printout does not have the web address on it. I hope it can be found via Google.

[schakel]

Originally Posted by Paul Scott

Schakel- I was trying to remember a piece by Bogotaj on sails where he points out that sweep and taper effect the amount of twist needed for a sail. Which seems to imply that more powered up twist (not luffing) equals more forward power, as the top of the sail is pointed more downwind than the bottom. Can you quantify how much power loss upwash causes?
Yipster, FWIW, Stradivarious, the new AC Tri, cants it's mast all over the place. If you haven't seen it yet, get on Youtube and search BMW Oracle Castleswreath. My wife and I video'd this, and it seemed to me that in addition to using cant to steer, they seemed to be playing with flow direction.
Some have speculated that mast rake is part of what makes windsurfers go so fast. A lot of classes allow a lot of rake- Contender comes to mind. I think I saw somewhere that the more rake made the boat faster.

Anyway, rake plus taper seems to equal more twist. And according to Bogotaj, fractional rigs too.

Paul

EDIT- I found the Bogotaj piece- 'How do sails work?' article by Paul Bogotaj. My printout does not have the web address on it. I hope it can be found via Google.

Loss of the main sail when under heel, but this is just high school physics, is the loss of wind compared to what you have with no heel. So the loss = cos*(angle of heel). in percentages of forwarding power.

Loss by the angle of twist is university physics and it takes me al night to figure that one out. If I do you be overwhelmed by the differential equations and Integrals and I do think you are waiting for that.

Main effect is what aeronautical engineers call down-wash which means the mass of air that is displaced by which angle per second.

Do you have Aero hydrodynamics of sailing, by C.A. Marchai in your library. I have so I know where to find it. (The academic answer)
But I do not have it here. If you are really interested I'll give you his equations as well.

[Paul B]

Originally Posted by Paul Scott

EDIT- I found the Bogotaj piece- 'How do sails work?' article by Paul Bogotaj. My printout does not have the web address on it. I hope it can be found via Google.

Bogotaj works for North Sails and his article is on their website:


http://www.northsailsod.com/articles/article6-1.html

[schakel]

I never knew why fractional rigs were used on my boats (a schakel and a dragon) Neither why the three top races have fractional rigs. (VOR, AC and Vendee Globe) I found it in the article from Paul Bogotai.

Thanks

[Paul Scott]

Originally Posted by schakel

I never knew why fractional rigs were used on my boats (a schakel and a dragon) Neither why the three top races have fractional rigs. (VOR, AC and Vendee Globe) I found it in the article from Paul Bogotai.

Thanks

Also why my ULDB Cruising sled (designed 1998) has a 3/4 rig.

I'm wondering how the Musto rig compares to an A Class(ish) rig, given the taper and rake of the Musto, vs much less taper and very little rake for the cat. IC typical sloop rig too.

Paul

[schakel]

I ask this before but nobody could answer.

Since you know something about it: How come the Hoyt boom was never used on fractional rigs. And then I mean a genua that goes halfway the jib of the main.

What is the big benefit. the torque of the genua is controlled in a way that easily follows or prepares the main for optimal half wind forwarding power.

Here is an nice picture of what I had in mind. But with an genua instead and a Hoyt boom that you can apply on long half wind legs.

The yard is K&M who are terrific. Designer is van der Stadt.
but Hoeke (Pilgim Project by Wally)
and Gerard Dijkstra (Maltese Falcon by Perinni Navi)

are also house designer.

http://www.kmy.nl/

[schakel]

[quote=schakel;233700]

Loss of the main sail when under heel, but this is just high school physics, is the loss of wind compared to what you have with no heel. So the loss = cos*(angle of heel). in percentages of forwarding power.
Loss by the angle of twist is university physics and it takes me all night to figure that one out. If I do you be overwhelmed by the differential equations and Integrals and I do think you are waiting for that
Main effect is what aeronautical engineers call down-wash which means the mass of air that is displaced by which angle per second.
Do you have Aero hydrodynamics of sailing, by C.A. Marchai in your library. I have so I know where to find it. (The academic answer)
Page 306 and 307 of Marchaj gives an impression of how the angle of up wash is related to the lift and drag ratio. The power loss of the up wash is related to the forwarding power (in aerodynamics these are similar to what they call Lift in wings) so The L/D ratio in the graphs give the overall gain. If L/D is greater than 1 the overall effect is positive.
In figure 2.61 page 306 the optimum of the sail is somewhere around 7 degrees to the apparent wind.
But in Fig 2.62 the influence of the cambered sail is shown as well as the influence of the velocity of the wind.
Even more interesting is the stunning effect of a wing sail which provides almost 2 times the forwarding power. I have a concept for a wing sail on the drawing board but it is confidential.

[yipster]

"Loss of the main sail when under heel, but this is just high school physics, is the loss of wind compared to what you have with no heel. So the loss = cos*(angle of heel). in percentages of forwarding power."

trying to get that in the calculator but playing with a degree arc i see 5% surface loss at 20 deg heel, 25% surface loss at 45deg heel and about 75% loss at 75 deg heel, is that basicly the same idea?

i like to have some idea but these calcs must be rough figers as sailcup, 3d wash or a winglet play a role as well

[schakel]

Originally Posted by yipster

"Loss of the main sail when under heel, but this is just high school physics, is the loss of wind compared to what you have with no heel. So the loss = cos*(angle of heel). in percentages of forwarding power."

trying to get that in the calculator but playing with a degree arc i see 5% surface loss at 20 deg heel, 25% surface loss at 45deg heel and about 75% loss at 75 deg heel, is that basicly the same idea?

i like to have some idea but these calcs must be rough figers as sailcup, 3d wash or a winglet play a role as well

The cos function in your calculator is perfectly right. What I always have on my mind is the graph.

http://www.ies.co.jp/math/java/trig/...graphCosX.html

[Mikko Brummer]

For those interested, we've posted a new article about sail aerodynamics at http://www.wb-sails.fi/news/Ad_aerodynamics

[tspeer]

Fantastic article, Mikko!

I especially liked the jet that impacts the lee side of the spinnaker - I'd not expected that.

[yipster]

http://en.wikipedia.org/wiki/Crab_claw_sail
re-reading Marchaj sail performance i'm impressed again with the crab claw
properly set it easy outperformes a bermuda or whatever other rig for that matter
the crab claw was only briefly discussed in this thread i see so i bring it up again

[Paul Scott]

And later, Marchaj displays the amazing superiority of a high AR Gunter, which has left me totally obsessed......

Paul

[brian eiland]

Originally Posted by Mikko Brummer

For those interested, we've posted a new article about sail aerodynamics at http://www.wb-sails.fi/news/Ad_aerodynamics

Hello Mikko,
You might go back and edit your posted reference to the website. I believe it should be
http://www.wb-sails.fi/news/Ad_aerodynamics/index.htm