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]

Originally Posted by Gilbert

It is called a Ljungstrom rig.

That's the one! Lundberg, duh!

[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]

Originally Posted by 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!!!

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]

Originally Posted by DanishBagger

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.