Biplane Rigs

[spidennis]

Eric,
Ok, that was a mouthful for me to chew on! so I went over to your website and I see you're certainly well versed in free standing masts and wishbone rigs!
http://www.sponbergyachtdesign.com/Masts.htm
It's gonna take me awhile to go thru all that you've got on your website, that's for dang sure but I know I need to study what you've done. You've done everything from dinghies to HUGE so you certainly got the full spectrum of experience!

I was thinking of incorporating windsurfing masts if I could, since I live in a really great place for it and kite boarding, south padre island, texas. Any advise you got will be seriously taken under consideration!

[tugboat]

Originally Posted by Eric Sponberg

A couple of things here which are not so: First, for a free-standing wishbone rig, cored laminates will not let you reduce the amount of carbon fiber. Such masts work by bending, and you need a certain minimum wall thickness to carry the loads, tension on one side of the mast, compression on the other, the stresses acting along the plane of the laminate (very high shear, by the way, on the leading and trailing edges.) If you core this type of laminate, you still need that basic thickness of carbon material because of the way the stresses are oriented. Cored construction in this regard does not buy you anything--the laminates have to be solid. Cored laminates in basic round-section masts will only add cost, complication, and weight.

Also, when you design such masts, one finds that if you keep increasing diameter, you will tend to reduce mast weight--i.e. you gain strength and stiffness quickly by increasing diameter and reducing wall thickness. But at the same time, you increase the chances that the mast wall will buckle under load before the fibers reach their inherent maximum strength and stiffness. In addition, aerodynamically, bigger sections are higher drag than smaller sections. So the key is to have the smallest diameter and the right amount of wall thickness consistent with strength and stiffness. That said, for any given boat, there comes to be a very narrow range of mast diameter and wall thickness that is pretty much ideal. The engineering trick is to figure out what that is. In my experience, for any given boat design and once you determine the loads on the mast, the wall thickness should be a minimum of 3% of the diameter--that gets you in the right ballpark. After you get there, then you have to figure out the laminate and what fabrics are going to go where--it cannot be all unidirectional; you have to have 0/90 and +/-45 deg fabrics in there.

Most carbon fiber is sized (i.e. coated) to accept epoxy resins, or epoxy-based vinylesters. Carbon can be sized to accept polyester resin, but these fabrics are much harder to come by, particularly in the limited quantities required to build a mast.

As for bearings, simple bearings (by which you probably mean journal bearings--without any rolling elements) only work on the smallest of mast designs. Anything above LOA = 30' really should have roller bearings made of hard materials--preferrably 300-level stainless steels (304, 316). Plastic rolling elements will deform easily under load, and that greatly increases rolling friction, really. Aluminum and bronze bearing bodies are OK.

Just some thougths from one who has been there, done that.

By the way, some of the boat designs shown so far look to have masts that are really spindly, and they are probably NOT designed and engineered to operate under very high loads--something to keep in mind. I also saw a picture of Team Phillips up there--you may recall that she had a catastrophic mast failure. I wasn't there nor was I asked to analyze it, but from the pictures and reports that I read, her masts looked to be very poorly designed and built. Nice concept, but it needed a lot of refinement for a better execution.

Eric

Well put Eric- I am not good at explaining my ideas- but pretty much i was trying to say that mast diameter can be stiffened the larger diameter you go and i thought erroneously that that might decrease costs with carbon..
I thought because his boat is not the size which requires a huge thickness of mast that he could use a composite mast. of course you certainly would know better than me... I was thinking though or roller bearing-correct me if i am wrong but couldn't you use a simple car axle type bearing? thats a roller(ball) bearing..of course maybe the they are similar in costs to a an application specific bearing such as a mast bearing??
I think though the wing masts such as those used on windsurfers are very stout? I wouldnt know the numbers but my guess is for two masts the materials couldnt be that expensive if done in c.f.? Im assuming you are talking about vaccum bagging and laminate type of mast?...im not sure what other options there would be..aluminum>? but i dont knwo if thast would have the right flexing properties? designing a mast is probably the hardest part of this project...

[Eric Sponberg]

Originally Posted by spidennis

Eric,
Ok, that was a mouthful for me to chew on! so I went over to your website and I see you're certainly well versed in free standing masts and wishbone rigs!
http://www.sponbergyachtdesign.com/Masts.htm
It's gonna take me awhile to go thru all that you've got on your website, that's for dang sure but I know I need to study what you've done. You've done everything from dinghies to HUGE so you certainly got the full spectrum of experience!

I was thinking of incorporating windsurfing masts if I could, since I live in a really great place for it and kite boarding, south padre island, texas. Any advise you got will be seriously taken under consideration!

I am glad you enjoy my website.

As for adapting windsurfer masts, been done before as seen by the pictures on this thread. This is just a matter of adapting the hardware that exists with such masts to match up with your boat. Windsurfer rigs are really very efficient aerodynamically, some are built better than others. Pick and choose and do the best that you can.

Eric

[Eric Sponberg]

Originally Posted by tugboat

Well put Eric- I am not good at explaining my ideas- but pretty much i was trying to say that mast diameter can be stiffened the larger diameter you go and i thought erroneously that that might decrease costs with carbon..
I thought because his boat is not the size which requires a huge thickness of mast that he could use a composite mast. of course you certainly would know better than me... I was thinking though or roller bearing-correct me if i am wrong but couldn't you use a simple car axle type bearing? thats a roller(ball) bearing..of course maybe the they are similar in costs to a an application specific bearing such as a mast bearing??
I think though the wing masts such as those used on windsurfers are very stout? I wouldnt know the numbers but my guess is for two masts the materials couldnt be that expensive if done in c.f.? Im assuming you are talking about vaccum bagging and laminate type of mast?...im not sure what other options there would be..aluminum>? but i dont knwo if thast would have the right flexing properties? designing a mast is probably the hardest part of this project...

Tugboat,

In general, automobile and truck bearings just aren't big enough for most masts. Plus, many of them are made with 400-level stainless steels which corrode like crazy in a marine environment--they'll get a layer of iron oxide on them in a week--not good. For the types of masts that make up the bulk of my design work, I am generally in the 8" diameter size and larger. Large bearings are available in that size, but they tend to be custom made (i.e. really expensive, and lead times are many months) and they are made of non-marine materials. So we sailors are left to our own devices. Lately, I have been advocating custom cast bronze bodies (i.e. silicon bronze) because they are relatively easy to model and cast. Then add 316 stainless steel rollers (can buy them just about anywhere, or make them in a good machine shop) and you can do this all relatively easily and cheaply.

There are windsurfer masts and there are windsurfer masts. Some are well made, some are not. Talk to the people who windsurf and they'll tell you who the better mast and rig suppliers are, and whether they'll last long. At the size boat you are talking about, 9.5 meters?, that may be a little big for a windsurfer rig. And windsurfer masts are not designed to carry a huge bending moment load as you would see on a multihull--compare the righting moment of your 9.5 meter boat to the righting moment of a windsurfer (one designs to maximum righting moment, or in the case of multihulls, a reduced fraction of righting moment--how much to reduce is a matter of opinion.) Windsurfer mast strength probably won't come close to what you require, at least in a free-standing configuration. Stayed rig may be another matter.

On small boats, actually, aluminum is a respectable choice because it is cheap and it is as stiff as most carbon fiber laminates (modulus of elasticity is 10 x 10^6 psi for aluminum, about the same as good quality carbon fiber mast laminates which tend to achieve 10 x 10^6 or 11 x 10^6 psi modulus). Strength in aluminum is not there, only about 40,000 psi for aluminum vs. 60,000 to 95,000 psi for carbon fiber laminates, depending on the layup and how much cloth and unidirectional material there is. Carbon fiber laminates are about 60% of the weight of aluminum equivalent structures, but on small boats with small masts, this is not important--only a small number of pounds of extra weight for aluminum. One advantage you have with carbon fiber is that you can tailor the laminate thickness and diameter through tapering of the mast. With aluminum, it is really hard to find tapered aluminum tubes in small sizes.

Eric

[Gary Baigent]

For sure, Eric knows encyclopedic and empirical stuff relating to unstayed masts and bearings - but on my wing masts, conventionally stayed though, not freestanding, (although I have done one free standing set, which failed elsewhere, by the way) I make my male/female bearings first out of simple old, but hard wood, then laminate layers of epoxy glue thickened glass over the male bearing and inside the cup, then after semi-curing, while the resin is still slightly soft (but dry), lap the two together (like valve grinding) to make a neat fit. After curing I waterproof grease the surfaces. Although this sounds very low tech, cheap and unsophisticated, those bearings last for decades, in fact Groucho's set are 30 years old now, no problems.
I kept thinking that Team Phillips could have saved themselves a huge pile of grief had they done something similar at mast base. At deck level, where the cantilever loads are extremely high, maybe a smooth carbon/Kevlar plain bearing could have done the job. KISS.

[spidennis]

Saw a comment on steamradio and tracked down what Derek Kelsail is up to. He has a facebook page: The new - "Kelsall Cat Rig", The twin wing rig with a difference.

http://www.facebook.com/notes/derek-...94891017266198

It starts out like this:

A rig for catamarans, which just makes sense.
Safer, excellent all round performance, lowest loading on all parts of the rig and structure, easy to handle, takes the hard work out of down wind steering, reef down wind, dump at least half the sail area on any tack and you can either build it or buy it. No need for lots of carbon either.

[Cat2Fold]

Hello all,
New member here. I am also the relatively new owner of Cat2fold. I bought her last May. I don't have a ton of sailing experience, so I'm not sure how much info I can give, but if there is anything I can help with, let me know!
After buying Cat2Fold in So. Cal, I took her out to Catalina for a long weekend.
Then I towed her home to the mountains of Idaho. I spent a week each on Jackson Lake (7,000' in Grand Teton National Park) and Yellowstone Lake (7,700' in Yellowstone National Park). It was a real trip having a 36' x 24' Catamaran on those lakes. Absolutely amazing!!!
After that, I signed up for the Baja-Haha 2011. Drove to L.A. by myself and set up Cat2Fold by myself then with a couple of friends for crew we sailed down to Cabo San Lucas with the Haha. We tied for first place in the multi-hull division!!! I commenced to sail around the Sea of Cortez for the next 5 months!
We did a bit more racing in Puerto Vallarta in January, and after finishing second in one race and first in the next, we were awarded second place Multi-Hull for the 2012 Vallarta Cup behind 63' Profligate.
Granted there wasn't much competition, and I really haven't sailed (or raced) much at all. This goes to show that the biplane rig doesn't take a rocket scientist to make go fairly fast. I am usually faster than most boats I sailed with (cruisers) without even trying. I can't say enough about how easy and fun this boat is to operate. It is not an overpowered race machine. But it is a huge platform that sails flat and fast (15.8 knot top speed) with a great view (thanks to the biplane).
I absolutely love my biplaned catamaran!!!
Cheers!
Brian
http://www.cat2fold.wordpress.com

PS- The word from Rafi is that the original single mast idea (50+ feet) wasn't sitting well with him as far as raising and lowering it and trailering such a long mast around. He made a 20' prototype biplane catamaran, liked it, and had Cat2Fold rigged for the Biplane while in New Zealand where the boat was built...