I was reading another forum discussion about the use of PVC as mast material. I believe (PAR) is our very own Paul R
http://boatdesign.net/forums/archive/ind...-7118.html
I have a laminated mast, a bit shorter than the specs, and am going to rig her as a sliding Gunter. I am concerned about the additional weight aloft, and that is why my search for solutions led me to the above site. Does anyone think that foam filled PVC is rigid enough to use with the Gunter set-up? Is there a good length/width recommendation? And is it also an alternative to a wood boom?
Why not use aluminum? I had an Oxford dinghy with a gunter that used an aluminum mast, boom and yard, the fittings were simply large stainless eyes through bolted on the yard and the boom that fit over the mast. The Mirror dinghies also use an aluminum gunter but the spars are attached with wood jaws. I think I would think twice about using pvc for anything beyond a test rig; the stuff is brittle, bendy and uv sensitive. not to mention the larger diam. stuff in schedule 40 isn't all that light anyway.
Just my oppion,
Jim
I remember the conversation on BoatDesign.net last year, I'm the same PAR. Since the crash we've all adopted our real names as handles, a new requirement on this forum.
This discussion followed over a few different threads, ultimately leaving the idea as a test, but dead to most any mast that carried more then 50 sq. ft. of sail.
Electrical conduit has a much thicker wall and is more UV stable than plumbing PVC. It still gets brittle with exposure to sunlight and isn't the lightest stuff to work with. Attachment with fasteners and adhesives, painting, overly flexible, brittleness, weight and other issues, really put a dent in the concept, except for the truly low budget, very small mast.
The Gunter rig is one of my least favorites. It has a lot of problems that aren't easy to cure. Other then historical requirements, I can find nothing to recommend it. There are reasons this rig has had so little development.
Loose footed booms need to be particularly stiff, so I'd opt for one of the common materials and methods for construction. Attached foot booms don't need to be quite as strong, but it's not a part you want a lot of flex in either. The Gunter yard has more need to remain stiff, as it forms the leading edge on the top of the sail. It has to be light and strong or it will sag off to leeward and bend out in the same direction, both bad things to do with your mainsail shape, heading into weather.
Spar weight is a pretty important consideration in small craft. This is why techniques have been adopted over the generations to insure light, but strong sticks. There are a number of spar building methods, and since this is basically the boat's "engine" I don't see the logic to skimp in this department. It's sort of like using questionable planking material.
What boat are you planning to place this rig on? Rig design (once it's placed) doesn't rely on formulas or guides so much as the loading calculations for the different functions. It's not terribly difficult work, but does require some understanding of the engineering involved, particularly if you're looking to venture very far out on the design limb.
Having sailed the gunter rig, I think the biggest advantage is the relativley short spar lengths. The yard basicly extends the peak of the sail well above the mast hieght. On the oxford the spars hung to the side of the mast creating less than perfect sail shape on one tack. The trade off was that all of the rigging could be droped into the boat beacause of the shorter spars. The Mirror Dinghy that uses a sliding gunter is one of the best performing 12 ft dinghys that I have encountered. I am not a gunter fanatic I am hoping to shed some light on the subject. I have built lateen, sprit and gaff rigs and they all have there places, it just depends on the boat and the intended use.
Jim