Building a New Rig! What to use for Tube?

Tapered alum extrusions are non existent as far as im aware, difficult to manufacture... would be nice if they were available???

So for a truly aerodynamic tapered oval type shape, you have no choice but to custom build it. And if your going to bother with this effort, you might aswell have it fully rotating aswell - why do a job half ***?

If you dont care about aerodynamic efficiency, and dont need a sail track - then by all means, look at saving some money by using pipe sections or as mike johns suggested, rectangle hollow sections - which have a higher section modulus than pipe of the same outside dimension and wall thickness.

 

Again, pipe sections are considerable weaker than tubing.

 

What makes a pipe a pipe and a tube a tube?

 

I suspect PAR meant that round pipe is weaker than oval tube assuming the same diameter, parent material, heat treatment and wall thickness.

Reason being that the pipe diameter is a constant and if the oval tube has the same width, it's length is going to be greater.

This is true but comes somewhere between a statement of the bleeding obvious and a 'so what?'

Especially as the OP has a gaff rig and the sails don't run in track.

PDW

 

Groper answered the second question well, that tapered aluminum mast sections are not available. Having said that, however, mast builders do frequently taper the top section above the top spreader or jumper struts to reduce chord and weight by cutting wedges out of the mast wall and welding the wall back together at the smaller size. Wall thickness is the same, a result of the extrusion process. You are right in that you must specify the biggest extrusion for the loads down low where they are greatest, and that means that the top of the mast is overbuilt.

That brings up the beauty of carbon fiber masts because they are relatively easy to taper in both section shape and wall thickness all along the mast. This can be done with wood masts too that are built-up sections. But aluminum extrusions rule the day because they are relatively cheap and easy to build.

As for X-rigging, I cannot answer why it has not caught on. Although we have seen a variation of the concept in the B&R rig (after Bergstrom and Ridder, the Swedish inventors). In this rig, the spreaders are swept well aft so that the backstay can be discarded. The shrouds are set up as diagonals and reverse diagonals in "X" patterns on both sides of the mast. This makes the spreader connections to the mast more rigid, and those points on the mast make the mast more rigid (mast does not minutely rotate at the spreader bases.) By being more rigid, the section size can be smaller--smaller wall thickness and/or smaller moments of inertia, all of which are good for reducing weight aloft and the form drag of the mast. Hunter Yachts used this type of rig on some models, and I used it on my design Bagatelle. I think Hunter's Child (being from the Hunter people) also used it.

Eric

 

Hi Eric.

I like the B&R rig because it allows big roach or square-top main without running backstays. It improves aerodynamics up high by increasing cord. Hunter has benefited greatly by using it. Beyond the aerodynamic improvement it saves allot of structure and weight in the hull. That said, B&R is nothing like X rigging through the mast. The wide swept spreaders eliminate the possibility of overlapping jibs and limit the sheeting of the main downwind. The rig pretty much requires a spiniker to sail deep downwind. The pre-bend and extra stays probably take B&R rig out of consideration for amateurs.

I agree that aluminum extrusions are simple to work with and provide good predictable performance at a reasonable price. Tapering is seen as a performance/cost add that is not worth it (keep that heat/stress away from my extrusion!)-obviously today the performance market is in carbon fiber. My thought is that there is a cost/foot mentality and a cost/pound mentality when what is needed is a cost/thrust consideration. Seen in this light I think that tapered composite rigs would be the standard.

 

Pipe is round a measured ID where the OD stays the same for threads no matter what sch it is for a given size . Tube is round, square, and rectangular and measured OD with wall thickness

 

Anyone have a picture or drawing of an X rigging ?
I've never seen one
Tom

 

X rigging examples

If you look up 2007 america's cup, NZL, Alingy, and BMW Oracle all had X rigs. It was essential to win upwind.

 

Thanks
Looks like it could get interesting tuning

 

As I recall, the 90+ ft 5 spreader AC rigs were very hard to tune. The adjustments are made at the the spreader tips. They had limited load cell technology and lasers for alignment.

On the other hand, there were no rig failures in the whole series which for AC is surprising, I think 2 hulls broke in half. They might have been badmouthing their own technology to keep the competition from copying a competitive feature they couldn't hide. The Xrig boats were clearly the 'haves' in the final standings.

The question of whether the Xrig is worthwhile on a cost/performance basis (as opposed to a kill ratio justification) is more complicated. The AC boats did it for sheeting angle. You could also keep the spreaders wider and use it to reduce compression, mast section, or the number of spreaders required.

A 2 spreader X rig could theoretically replace a 4 spreader conventional rig of the same dimensions (height, width, and section) -which of those would you rather keep tuned?

 

These guys (among others) offer tapered aluminum (and steel) poles in many wall thicknesses, diameters, and lengths up to 40'......

http://www.hapco.com/

 

Go get a professionally built mast. Updating the mast design will change the boat in a very positive way. It will be worth the cost and effort. You have some of the right ideas but you can buy someone's time and tricks that have been accumulated over sometimes lifetimes. Thick a walled mast is normally a bad idea.

Most of us on this list have developed ideas from coping what works, changing to get something better and building up in size over time. You're going right to a really big highly loaded system. The key here is the mast is a system. You get it wrong and some can die.