Proa rig questions
Hi all first post. I am designing a 7.5 m beach camping proa that will use a hobie 16 rig and sails that i already have with the intention of upgrading to a larger rig once funds become available.
My question relates to mast placement. My proa will be rigged similar to Jzerro and Madness style but i dont know how far offset the mast needs to be so that the fore/back stays dont interfere with the main sail. How far to windward does the rig need to be? Would 500mm be enough?
Cheers for any help
Dave
Hi Dave, welcome to the forum.
I’m no rigging expert, but I suspect there may be more than one way to approach the problem.
The Hobie 16 has a 3 stay rig, with no back stay. The main sheet block is on a traveler, and I suspect main sheet tension is important not only to sail shape, but also to the rig’s integrity (it takes a lot of force).
One solution is to try to preserve the Hobie 16’s rig geometry on the proa. Put the mast so that traveler rests the lee edge of the main hull. That dictates the mast placement. Then run the stays at the same angle, and hopefully the side stays end up on the main hull, and the forestay ends at the ama. Then you’d hoist the jib on one or the other side stay. However, the stay’s angle is not optimum (tack to lee), and might cause sheeting problems. But the main would probably behave well.
If you change all the stays to optimize jib angle and sheeting, then you’ve got a totally new rig. One thing you could do is reef the main sail so that it’s shorter than the mast. It would have a better change of going under the side and back stays.
I’m curious to see what you come up with. Please keep us posted.
If you build a crude and simple cardboard model of your proa its very easy to pull it with a string in the bathtub. You can very quickly find the balance-point and design the rig around that.
Cheers
Johannes
Thanks for the replies guys.
I did a small scale model of the rig on a bench, and I am pretty sure the Hobie 16 rig is not going to work. The boom is too long and the Main sail leach will be touching the backstay before even being close hauled.
I think I need a taller rig with a shorter boom so the sails and stays dont get in each others way.
Does anyone have experience with free standing rigs? No stays to get in the way would be handy!
I am thinking a schooner rig, with two 8 metre tall plywood wing masts, with a 4 metre Aluminium or Carbon tube built in, say 3 metres in the mast with 1 metre into the hull, any guesses as to whether it will stand up or not?
Cheers, Dave from Australia
You can always build a plywood wingmast strong enough, but the weight can be a problem. If you want a freestanding mast i would recomend a junkrig and junksail.
Another option would be a Ljungströms-rig with some kind of wishbone-boom.
Cheers
Johannes
I believe Jzero had a modified Hobie rig, with a different.
Wing mast and the like are going to add a lot of cost and complication.
Why not just have a longer hull? (or even bow-sprits).
You will still get a very good performance and be on the water more quickly, which is what it is all about.
Mark
Look at production boats with free standing rigs for ideas - Laser, Sea Pearl, Wilie. Or consider a soft wing sail, like Wharram used on his Tiki cats.
Or, build stout stub masts and use 2 big windsurfer rigs. There’s a picture of a proa using windsurfer sails here:
http://proafile.com/forums/viewthread/114/
Apparently, sheets are optional if you have friends :o)
Curtis
I did a small scale model of the rig on a bench, and I am pretty sure the Hobie 16 rig is not going to work. The boom is too long
The boom would hit the stay when caught aback? A solution to that would be to take the stay further out. You should be able to get 3.7 m between mast and where the stay attaches to the hull, if you don’t insist on maintaining the same spacing as on the Hobie 16. You may want to maintain that spacing on the assumption that you want to keep the aerodynamics as designed. An argument against is that you want to shift the centre of pressure further forward than on the Hobie.
the Main sail leach will be touching the backstay before even being close hauled.
That seems a more serious problem. But have you taken twist into account? That gives you a bit more room, the more so the further out on the hull the stays are attached. That makes the stays cross the leach higher up, where the sail has twisted off some more.
If you contemplate doing as much work as building a wing mast, consider instead the possibility of using a wing or just a strong enough round spar as your weather stay. Then you can spread out the lee stays to the hull ends to a wider angle without having to worry about breaking the mast through compression or the lee hull through bending when you get caught aback. The weather spar would take the compression, the lee stays would only need to be tight enough to prevent the mast from lifting out of the socket.
The Hobie 16 jib was never intended to be quickly taken down or set on the water. How do you plan to deal with that?
Although it means blowing my own trumpet, you might look at the two rigs proposed in this thread: http://proafile.com/forums/viewthread/94/. The first means making new jibs, but because the shape comes from the battens, you would not need any broad seaming except at the lowest batten, so you could do it yourself. If you want only one stay sail, the second rig lets you do that. But if you want to make the jib easy to handle without lots of adjustment of sheeting angle, rig it as a balance jib, and attach the boom far enough to the lee of the weather spar that the jib’s luff can clear it. That issue has been discussed in this thread: http://proafile.com/forums/viewthread/135/. I just propose you put your jib on the weather side.
Regards
Robert Biegler
http://www.junkrigassociation.org/Resources/Documents/Arne Kverneland’s files/The poor man’s Ljungsröm Rig, ver. 20110722.pdf]Ljungström PDF
I found this article. I like his “review” in the last part of the PDF.
Cheers
Johannes