Lateen sail. ?'s

[upchurchmr]

JimD,

Thats very neat looking. Have you been looking at the Mast Aft and other threads by Brian Eiland? Most of the discussion is about bigger boats, but there might be something there for you.

Sort of looks like you don't need any other ideas.

Please post a sailing report when you can.

[JimD]

JimD,

Thats very neat looking. Have you been looking at the Mast Aft and other threads by Brian Eiland? Most of the discussion is about bigger boats, but there might be something there for you.

Sort of looks like you don't need any other ideas.

Please post a sailing report when you can.

Upchurchmr, I wasn't aware of the Mast Aft thread or Brian's other ideas. I shall search them out. Thanks for the tip. I have high hopes for this boat. It has unfolded after many false starts and changes in direction because I couldn't make up my mind as to what I wanted it to primarily be. But its turning out ok, very light weight and versatile. The main hull can still be paddled like a kayak without the outrigger, or paddled with the outrigger hopefully with very little weight and drag penalty, or sailed. We shall see.

[upchurchmr]

JimD,

Forgot to say that those threads were on boatdesign.net not woodenboat.
http://www.boatdesign.net/forums/sai...-rigs-623.html is different but same subject
http://www.runningtideyachts.com/arc...rmansboat1.php may not be exactly but similar subject
http://www.boatdesign.net/forums/mul...rig-21274.html another but directly related
http://www.runningtideyachts.com/sail/ this may be exactly the same as #2 above.
WishBone Sailing Rig
http://www.boatdesign.net/forums/sho...6&postcount=34
http://www.boatdesign.net/forums/sho...7&postcount=33
http://www.boatdesign.net/forums/boa...ast-25696.html
http://www.sail-the-difference.com/DESIGN.28.0.html bigger and I am overloading you

There was also an Austrailian who had a discussion about his 60' a frame mast from which he flew 2 geonas. It was very interesting but I cannot find it. He was trying to sell the boat, something about a divorce.

Have fun if you can stand all that. Aft Mast rigs is a very long thread.

Marc

[JimD]

Marc, from one of your links:

Any study of rig effectivness points out that on a per-area basis, jibs are more effective than mainsails. That leads to the conclusion that rigs would better if they were all jib - hence the mast aft rig. What these studies often fail to point out is the effectiveness of the jib comes from its interaction with the main. On its own, it doesn't perform as well. And theoretically the main suffers in the exchange, making it look worse. But the combination is more than either sail acting in isolation.

The finest article I've ever read on the interaction of multiple lifting surfaces is A.M.O. Smith's 1975 Wright Brother's Lecture, "High Lift Aerodynamics" (AIAA Journal of Aircraft, Vol. 12, No. 6, June 1975, pp. 501-530.). He goes into great detail on the five primary effects of slotted airfoils and how they contribute to high lift. Very illuminating with regard to the main/jib interaction.


Then there's the problem of the mast. It's almost impossible to fair an isolated mast because of the range in apparent wind angles. The apparent wind will meet the mast from 20 - 30 degrees either direction. No section shape for the mast will avoid massive separation under these conditions, causing a lot of drag. The drag of a circular cylinder can be the same as an airfoil ten times its thickness and a hundred times longer - with drag coefficients based greater than one. In other words, the drag of an isolated mast can be almost as much per square foot as the sail produces in lift per square foot! When you add up the frontal area of the mast plus any struts and rigging, you get a lot of windage.

The mainsail acts as a splitter plate behind the mast on a conventional rig, preventing the formation of a Karman vortex street in the wake of mast, and the favorable pressure gradient in the slot allows the flow to reattach to the mainsail, minimizing the separation behind the mast. Finally, the jib channels the airflow so that it hits the mast from a much narrower range of angles, making it feasible to reduce its drag by elongating its cross section. So the drag of the mast in a conventional rig is much less than the same mast standing by itself in a mast-aft rig.

Lastly there're the structural considerations. A mast aft rig, especially one that is inclined forward, makes it very difficult to maintain adequate tension in the forestay, leading to lots of sag. The forestay is longer, and the angle between forestay and mast is larger than the angle between backstay and mast. This means the loads on the backstay are far higher than the loads on the forestay, and the mast compression is much greater to achieve a forestay tension anywhere near that of the conventional rig. Making the mast larger, heavier, and needing additional reinforcement to stiffen the boat. You could mitigate some of these problems by mounting the mast more midships and raking it steeply aft to put the hounds at the same location. This would shift the mechanical advantage of the forestay and backstay.

The point about tensioning the forestay and the stress on the shrouds acting as back stays is what I noticed when setting up even my tiny rig. Since I added the aft mast step as an afterthought there's not much I can do about it now without cutting the boat open again which I am loath to do so we'll just experiment and see how it goes. I think an stayed tabernacle design might work for these small rigs, possibly with a single back stay. Something to think about for next time. The aluminum step I used here:

[ahp]

They did pass the yard around the mast when tacking, even on these big xebecs. It was a very well coordinated process by an experience crew however.

[JimD]

They did pass the yard around the mast when tacking, even on these big xebecs. It was a very well coordinated process by an experience crew however.

Doing my best to resist every urge to make this boat more complicated than it has to be. Although if I get around to building a taller mast to accommodate the larger jib I have available it will definitely have a boom. But that sail is cut differently so it will easily accomodate a boom swinging freely in front of the mast. I have a two inch aluminum tube 16 feet long I could use as the mast for the bigger jib but would prefer to keep the spars wooden.

[upchurchmr]

Jim,

There are lots of conflicting discussions on main/ jib interaction.
I might point out that aircraft have no separate "jib/ main" - I.E., they have a single wing. The only aircraft that have a leading edge slat are intended for very slow flight and are seriously limited when they try to fly faster.
It may well be that jibs which are cut and typically set in combination with a main would need a different shape or setting to produce full power. Realistically the problem is that the triangular shape required is limited in area compared to a main with lots of roach (daysailing cats) for a given height of mast.

When you desire to go overboard, you could add a bowsprit and a genoa (another jib forward)to get more area.

The mast typically is circular. There have been lots of experiments with turbulence stimulators to reduce round section drag. I might be able to find something which could illustrate that. Actually using a birds mouth mast which is not smoothed out to be circular might approach the minimum drag section. Of course the stimulators are most effective at a given height which is related to the wind speed. An alternate is to make an airfoil covering which would rotate to face the wind and reduce the drag. This would be a lots of work and complication - I would agree with your desire to simplify if it was my boat.

Read some more, there should be someone articulate to disagree with the quote your gave, allowing you to happily go your own way. The only reason I included all the links was to give you more ideas.

Marc

[JimD]

...

When you desire to go overboard, you could add a bowsprit and a genoa (another jib forward)to get more area.

...

Marc

Marc, actually, the other higher aspect jib I have might be perfect to fly together with this smaller jib I'm starting out with. So I may end up going overboard, as you say, at some future point.