Split Mainsail. Has this been tried before?

[Omeron]

A very simple and fun mainsail idea occurred to me.
I wonder whether this has ever been tried before?
Imagine the boom is split vertically and opens up like scissors.
The mast side is fixed (pivoted) and the clew end opens to
port and starboard sides as far as possible.
The mainsail is made of two identical layers.
When reaching, the boom is closed and you have a normal sail,except that it has two layers instead of one.
If you are running, ideally dead downwind, you open the boom and
you have double the mainsail, like butterfly wings.
Since pressure on sails are much less when running, the thinner layer
on each side should be ok. or in other words, you do not start with
double the cloth when reaching.
If the wind increases you just close the angle,and decrease the projected area. So no need to reef either.
Spring load the boom, so if you release a line it opens by itself.
Sounds like a stupidly simple way of doubling your sail area when running.
Not for racing perhaps, but might be interesting for long offshore passages,like double wing to wing headsails.
What do you think?

[PI Design]

I think that is called a Lundberg rig. There is a bit on it in Marchaj's books, but I've never seen one. Sounds fun though.

[DanishBagger]

Would be great on a catboat, methinks (not that they need much more sail area as it is).

[DanishBagger]

Here we go (had to find an external harddisk to really show the size of the sail):

[Gilbert]

It is called a Ljungstrom rig.

[PI Design]

It is called a Ljungstrom rig.

That's the one! Lundberg, duh!:rolleyes:

[Omeron]

Yes, Ljungstrom rig is very close. But they do not seem to deploy booms.
What i had in mind is really a very conventional setup with the exception that it is an open and shut case!!!

[DanishBagger]

Yes, Ljungstrom rig is very close. But they do not seem to deploy booms.
What i had in mind is really a very conventional setup with the exception that it is an open and shut case!!!

You could even make it a design feature of the boom tent – it could be sort of triangular (seen from above)

I just woke up (literally, so I'm sorry if I'm not coherent), but I am returning to your thinking that you could use thinner cloth than one would with a single boom. I'm a bit in doubt whether that would work. The reason being that - for obvious reasons – one side of the cloth have no way of transferring the forces to the second layer. They're not connected in any way. On one tack, one of the sides will take all of the forces, and on the other, well, the other will. Unless, of course, they're exactly the same, and they have been adjusted the exact same way. I don't think that's possible, especially with stretch playing into it.

[Omeron]

Well, i see your point, but i do not think the windward side would take all of the load, as there is an identical layer behind it. Perhaps a 60/40 situation.
Imagine supporting your sail horizontally and filling it up with water.
It would make a big difference whether you had just one layer or two.
I love the boom tent idea as well.
Especially thinking that the greatest shade would be over the helm.
How about an emergency brake function.
Just open the flaps and come to a screeching halt.
And in no wind, you can just flap your wings...
Might be a real sight, entering into a marina on a dead calm day...

[DanishBagger]

The brake is an awesome idea! Flip the booms out on both sides, and voila!
Or if motoring and with the tent up: flip the booms up on each side of the mast.

Also, the boom tent could be used as a huge rain catcher. A gigantic funnel to a deck filler near the mast.

Seriously, one should consider adding a secondary boom (could be a bit thinner on a "normal" boat. Or perhaps a spinnaker pole could be used for the same in some of the circumstances (boom tent, rain catcher, brake)?

If the boat was a gaffer, you'd get extreme downwind capabilities. and speaking of rain catching, imagine lowering the peak(s), spreading out the booms as much as they can – even a light drizzle will catch plenty of water.

Hmm, come to think of it: A boomless main would be a nice candidate (no fingers or heads squished between the booms) – especially if done with numerous full battens.

I think one should consider low-stress rigs for this kind of fun. Gaff rigs, luggers and so on. Especially if you want to try to fluff your way into harbour ;-)

[Hansen Aerosprt]

We patented this system in 1987. A double-sided, fully battened wing sail which open up into a spinnaker shape downwind. Several working examples were built with good performance upwind and down.
- Bill Hansen

[DanishBagger]

I doubt that patent will hold water over here, but even so, it does look nice, and I especially like the idea that it opens up into a spinnaker.

One thing, though:
What will happen if you're not going dead downwind? I foresee some trouble trying to get the "hinge" to line up with the mast. How do you go about that?

[DanishBagger]

nevermind, I see now, that not only do you have battens, you also have booms – and by that I have the answer.

[Hansen Aerosprt]

I doubt that patent will hold water over here, Danish:
Patent is 22 years old so it doesn't matter. Nevertheless, why do you say this? Actually, this system works very well and is pretty simple in concept. The sail cost is higher but overall probably less than a conventional rig and main, spinnaker, etc.
- Bill

[DanishBagger]

Well, I mentioned it, because it seemed as if you were trying to stifle the discussion by mentioning you held a patent. As if you were saying "don't touch this - I own the rights". But if you didn't I apologise.

I still like the idea – and I think it would look cool on a high-peaked gaffer.

[Hansen Aerosprt]

Well, I mentioned it, because it seemed as if you were trying to stifle the discussion by mentioning you held a patent. As if you were saying "don't touch this - I own the rights". But if you didn't I apologise.

I still like the idea – and I think it would look cool on a high-peaked gaffer.No intention to stifle discussion on a sailing development I worked very hard on which is still relevant today. A patent is simply a means of laying out publically a description of an invention or process in exchange for a period of exclusivity (which maybe be transferred via licensing, etc.) Seems you choose to immediately attack it's validity rather than continue the discussion. That is why I asked. In any case, anyone out there is free to use the development as they wish. If they need help building one, they have at least one source to look at and know who to contact.
- Bill

[DanishBagger]

Hmm, if I am not mistaken, a patent is in my book something you take out to protect your investment. Not something you do in order to share the stuff.

I didn't decide to "attack" out of the blue. Your headline states which patent it is, for one, and the first sentence reads:

We patented this system in 1987.

That to me is an indicator, not of willingless to share, but rather a defense of the mentioned exclusivity. I can see that you _meant_ something else, but reacting to what you actually wrote in that form you wrote it, really cannot be called an attack. But whatever floats your boat.

[MalSmith]

Hmm, if I am not mistaken, a patent is in my book something you take out to protect your investment. Not something you do in order to share the stuff.



As I understand it, the original intent of the patent system was to prevent ideas from being lost by encouraging people to publish them. Hence the deal is that you get a limited period of exclusivity in return for public discolsure.

Mal.

[Hansen Aerosprt]

Hmm, if I am not mistaken, a patent is in my book something you take out to protect your investment. Not something you do in order to share the stuff.

I didn't decide to "attack" out of the blue. Your headline states which patent it is, for one, and the first sentence reads:

That to me is an indicator, not of willingless to share, but rather a defense of the mentioned exclusivity. I can see that you _meant_ something else, but reacting to what you actually wrote in that form you wrote it, really cannot be called an attack. But whatever floats your boat.Bagger:
I wrote: "We patented this system in 1987." Simple fact. Then I explained what it was. Never mentioned exclusivity or protecting anything.
Your first reply was: "I doubt that patent will hold water over here."
That was why I asked you the reason for this. In any case, glad you like the idea. Time to move on. Now, anyone interested in building one? How about on this boat?

[Omeron]

This is not exactly what i was trying to describe, but also very interesting.
In this world of every crazy idea finding an application, how come this has never been tried?

[DanishBagger]

Okay, Hansen – I guess we both overreacted. I can agree to that. Truce?

[BOATMIK]

Yes, Ljungstrom rig is very close. But they do not seem to deploy booms.
What i had in mind is really a very conventional setup with the exception that it is an open and shut case!!!

I am deeply concerned about this idea.

Should a crewperson be caught between the two sides of the sail at the bottom mark it might be necessary to wait until the top mark to release them.

Or potentially it might be a possibility that a crewmember could be misplaced.

5, 6, 7, 8 ...

Eight!

Geez, has anyone seen Steve?

Steve, Speak to me Buddy ...

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