sail aerodynamics

[sigurd]

the first one worked too. great article.

[brian eiland]

Traditional cargo boat being sailed in Martinique. These things can move! Thanks to anarchist Jon from Dockwise Yacht Transport.

...or maybe this is the utilmate square top main (and jib)

[john schroeder]

Brian , Leave it up to you to drop a new idea on us or a very old being used well. I like the movie Water world with the catamaran and the mast that extends up I always though a telescoping mast bowsprit and boom .

[Guest625101138]

Originally Posted by john schroeder

Brian , Leave it up to you to drop a new idea on us or a very old being used well. I like the movie Water world with the catamaran and the mast that extends up I always though a telescoping mast bowsprit and boom .

Waterworld is my favourite movie with my favourite movie star - the mariners trimaran. I loved the way it transformed into a speed machine.

[schakel]

Originally Posted by Rick Willoughby

Waterworld is my favourite movie with my favourite movie star - the mariners trimaran. I loved the way it transformed into a speed machine.

Rick W

You are right about the tri in Waterworld it is awesome. It was build by Henri Jeaunneau for Beneteau. Here is his resume:
http://www.sailboatdata.com/view_BUI...?Builder_ID=48

Notice he also build some of the AC boats. Great!

But a telescopic mast is something I only saw in that movie. The speed the tri makes while he stands in the crow nest looks very, very cool. That most of the crew was under deck while filming is to be guest.

[Milan]

Originally Posted by Rick Willoughby

… my favourite movie star - the mariners trimaran. I loved the way it transformed into a speed machine….

Yes, it does look very nice in the film, unfortunately, it can’t work in reality. They actually had two trimarans in the film, one in the sailing, other in the windmill mode.

http://www.geocities.com/mariner767/index.html

[schakel]

To be very precise the yard was Jeaunneau and the designers were Marc VAN PETEGHEM and Vincent LAURIOT-PREVOST Thanks for the nice site about the mariners’ catamaran Milan

[brian eiland]

Just saw this interesting comment submitted to Scuttlebutt by an aero associate of the North loft

* From Paul Bogataj:
Since the Deed of Gift provides the Challenger a "match for this Cup with a
yacht or vessel propelled by sails only and constructed in the country to
which the challenging Club belongs ...", isn't there another question before
one even gets to the issue regarding where the yacht was constructed? Is the
wing a sail? What defines a sail? Is it anything that pulls a boat through
the water using force extracted from the wind (like a kite)?

Why would there be different words for sail, wing, and kite? They may
perform similar aerodynamic functions, but they have different
characteristics that define them as different things. Perhaps a sail is
something that is flexible and is capable of being raised and lowered along
the mast. It seems that there is more potential legal arguing, unless they
do not intend to race with the wing.

Curmudgeon's Comment:
Here is the definition from Wikipedia: "A sail is any type of surface intended to generate thrust by being placed in a wind...in essence a vertically-oriented wing. Sails are used in sailing." And, of course, there is the precedent from the 1988 Match when Stars & Stripes (USA) successfully defended the 27th Match with a wing-powered catamaran.

[CT 249]

If a sail is only something that can be raised and lowered along with mast, what do Lasers, windsurfers, Moths, and 12, 16 and 18 Foot Skiffs have?

[RHough]

For a change in pace ...

Why are overlapping head sails faster?

Seems that the two sails on a sloop are considered as one aerodynamic unit with one circulation pattern.

Just how effective is the overlapping area of large Genoa when sailing upwind.

I get that on a reach the two sails are not a single element, but when trimmed for sailing upwind why (how?) does an overlapping Genoa increase drive?

[Doug Lord]

And why wouldn't a "ribbon jib" that has a very short chord and covers the entire luff of the main be fast?

[sharpii2]

Originally Posted by RHough

For a change in pace ...

Why are overlapping head sails faster?

Seems that the two sails on a sloop are considered as one aerodynamic unit with one circulation pattern.

Just how effective is the overlapping area of large Genoa when sailing upwind.

I get that on a reach the two sails are not a single element, but when trimmed for sailing upwind why (how?) does an overlapping Genoa increase drive?

That's because the jib is actually doing most of the work. Making the jib bigger, even along the foot, improves the drive much more than adding the same area to the main.

This is why, when sail area was heavily counted, the mast head rig came into prominence. It had the bigger jib. Later, the mast was moved aft, making the main a ghost of its former self, and making the jib an even greater portion of the sail plan.

When Sail Area became less heavily counted, it made more sense to go with a bigger main, because there are real limits on how large you can make the jib. It's size is limited by the length of the boat and, to some extent, its width. It needs stiff staying to work properly.

The main can have a longer boom, can be extended well past the upper shrouds, and have a wide roach put in it. It takes a lot less staying to make a main stand well. Therefore, doubling the area of the main, after a certain point, becomes much easier than doubling that of the jib.

[sharpii2]

Originally Posted by 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

1.) How do you reef it?
2.) Wouldn't comparing it to a well vanged, low aspect ratio Bermuda cat rig be a more fair comparison.

It seems that the big advantage the Crab Claw has is that the boom and the yard are connected ahead of the mast, allowing next to no twist.

I wonder how well it would compare to a low aspect ratio, Boomed Lateen sail, which can come close to matching both advantages?

[Paul B]

Originally Posted by RHough

For a change in pace ...

Why are overlapping head sails faster?

Seems that the two sails on a sloop are considered as one aerodynamic unit with one circulation pattern.

Just how effective is the overlapping area of large Genoa when sailing upwind.

I get that on a reach the two sails are not a single element, but when trimmed for sailing upwind why (how?) does an overlapping Genoa increase drive?

I can tell you that about 30 years ago North Sails was doing a lot of development in the J24 class. They had designers on both coasts working on all sorts of shapes.

I was invited along on a testing session when the guys from back East came out to test shapes against the West coast designs. We traded boats, sails, trimmers, and drivers for a couple of days in a variety of conditions, two boat testing.

The first morning it was very light, maybe 5 knots, as we went out. We were sailing in perfectly flat water, and we wanted to put up a jib that had not been out of the bag at the dock. So we put it up to take a look at fit, even though it was too light. The other boat put up one of their genoas.

We came together and started straight lining. We were surprised how well we could hang in with only a jib up. Everyone was laughing, and some fun was being poked at the designer of the genoa on the other boat.

As soon as we hit the first of the lump we went out the back door pretty quickly.

That day makes me think that the difference has a lot to do with stall. The higher aspect headsail stalls more easily than the overlapping, lower aspect headsail. So the genoa is more forgiving, with a wider groove. In fact, in J24s we used to hang onto the genoa as long as possible if it was lumpy. If you changed down in big lump you would be blown out the back. Ugly overpowered worked better than flatter and feeling in control.

Also, for the same chord thickness the longer sail is deeper, so more powerful. It should generate more lift.

We have just changed from sailing a OD48 (genoas) to sailing a Farr 40 (jibs). The driver is telling me it is harder to keep in the groove.

One other thing to consider is the ACC boats kept getting more overlap with each generation. I think the location of the vent in the overall foil (both sails together) is critical. It needs to be in a location to help the flow stay attached where it wants to break away. I don't think that location is so far forward in the overall foil to make a non-overlapper make sense.

I'll bet a smart sail designer could come on here and make it vary simple to understand. I'll bet there are some nice photos of wind tunnel testing that shows the best location for the vent.

[Paul B]

Originally Posted by sharpii2

This is why, when sail area was heavily counted, the mast head rig came into prominence. It had the bigger jib. Later, the mast was moved aft, making the main a ghost of its former self, and making the jib an even greater portion of the sail plan.

When Sail Area became less heavily counted, it made more sense to go with a bigger main, because there are real limits on how large you can make the jib.

If you are talking about the end of the CCA rule/early IOR rule era this is not the reason.

The shift to larger headsails was due to rating advantage and the limitations of available sail material of the time.