**** and bull ramblings, but you should so more respect where it is due.

The SC 22 (ACR22) carbon hulls are a work of art. They are beautifully finished, amazingly stiff/strong, and very light. Bill has designed and built a least six designs, that I am aware of. How many have you brought to the water? I suggest that until you establish yourself as an authority, that you show more respect for Mr. Roberts.

If you want to talk about your comparative sailing skills.....well, I definately would not go there!

Wouter, until you prove yourself as a sailor, designer, or anything else dealing with catamarans, you should pick your fights a little better.

Bill, I would not dignify Wouter with response.

Regards,

W.F.
Bill Roberts Fan

Bill,

I didn't misuse your information Bill, I just pointed out that you can't use the 3rd order approach to proof that the RC30 hulls are indeed light for their size.

In simple terms teh RC30 hull are not at all similar to a 18 foot platform that is scaled up by a factor of 1,66 in all directions.

The RC30 hull maybe be 1,66 the length of an 18 foot hull but it is more likely to be only 1.3 times the width and depth.

By assuming it is nothing more than a scaled up 18 foot hull with the same factor for all dimension you made it look like a comparable 18 foot hull would have to be lighter than what anybody else is producing at this time. Including A-cat hulls.

If we would continue the 3rd order approach to 16 foot cats than a Taipan hull of 22 kg's has to be only 12 kilograms to be equivalent to your RC30 hull.

That is why I made the calcs that compared displacement of both boats. You will find that displacement doesn't follow a 3rd order trend either so why would hull contruction be accurately described by it. Afterall displacement is the most important design parameter when designing a cat hull.

Bill, I truelly respect your vast amount of experience, standing and the cats designed by you but when it comes down to applying formula's I've found myself to be in strong disagreement with you.

And may post are just that; disagreements on how formulas like Froudes law are used and applied. Nothing more,

Wouter

Why exactly would it cost so much to lighten the boat up if the hulls are already, as you say, relatively low in weight in the first place?

Doing the things to really lighten the boat would include things like:
Dynaform wire or carbon standing rigging
carbon beams
carbon rudder castings
carbon mast
carbon boom
(seems like a lot of carbon hu?)
Ti bolts and metal fittings

the cost/lb is MUCH higher for the carbon parts. I was told what a set of carbon standing rigging for the M20 costs (have forgotten it now), but I amazed by it's cost. As a comparison, the I-20 mast costs something around 3500 dollars (if I remember right), the 6.0 mast is like 1600 i think (don't quote me). I'm sure that Bill's 27/30 mast is not cheap in AL and the cost of a mast goes up exponentially with it's length (last I heard an ACC mast ran something like 1/2 million...don't quote me again...just working from little bits of memory)

Things like beams and castings made of carbon are also substantially more expensive than their AL counterparts. You hit what we called in engineering class a point of diminishing returns. You can keep dumping money in, but the weight you save/dollar keeps going down.

Bill saves the big pounds where it is easy (in the hulls). By building in carbon, not only does it save weight, but it also increases the life of the product. I have to admit that I don't really agree with the way that either Bill or Wouter are trying to scale hulls and boats up or down in weight. Bill is building in carbon while most boats are glass (apples and oranges). I think to properly compare the two, you must use the same build process.

There are also some other weight factors that will not change as much with size as some things do. No matter the size of the boat, there will be a minimum attainable weight in rigging. As the boat goes up in size, the rigging does not change as drastically in weight as does say the hull weight (just an example, there are several other things that would follow the same principle).

The only reason I participated in this conversation was to try and add another view, learn some and hopefully get some feed back on my thoughts. It's been fun, hope this doesn't turn into a name calling contest.

Will

p.s. this has got to be some sort of record setting post

Come to think of it.

Wouldn't the ratio of hullweight / displacement be a more appropriet measure ?

Wouter

Bill,
Why would anyone want to have a mast that slides back and forth on the beam? That's ridiculous.

This all started with the question as to whether wings will have essentially the same effect, as far as righting moment, as having a wider boat.

Luiz said, I believe, that it will increase the righting moment but it will be offset some by the wing on the opposite side. He added that the real benefit of a wider boat is that the leeward hull (being farther away from the mast) plays a greater role in reducing heeling moment than it does on a narrower boat.

So I conjectured in a totally non-serious way, that the only way to make a narrow cat act more like a wider cat is to have a hiking rack only on the windward side to increase the righting moment and also slide the whole mast to windward, so the leeward hull could help to reduce heeling moment.

For instance, the difference in width between a trailerable boat and a Tornado is 1.5 feet. So if you slide the mast to windward 9 inches, you would have, in effect, a 10-foot wide boat on the leeward side because of the increased distance from mast to leeward hull, and (at least)a 10-foot wide boat on the windward side, as well, because of the ability to get crew weight out farther.

And all this is assuming that you are sailing in enough wind that you NEED to increase righting moment and reduce heeling moment.

I haven't yet asked the question as to whether wider boats have an advantage in light air where all these "moment" things are not an issue.

Hello MauganH17,
The answer to your question is tooling costs. One can use the same hull mold to build fiberglass or carbon composite parts. To build any composite part, a mold is required. So to build all of the parts that are metal now, tubes and brackets etc, require molds, molds that do not exist now.
Bill

Hi Mary,
On a 10ft wide boat the center of gravity of the boat platform is 5ft from the leeward hull center of bouyancy. This is 9 inches further to windward from the leeward hull than on an 8.5ft wide boat as you said. Moving the mast 9 inches to windward won't quite compensate for the 8.5ft vs 10ft wide boat difference because you are moving only the mast and not the center of gravity of the whole boat. In the case of the Tornado, for example, you are moving only 60 pounds of mast and sails and rigging weight to windward 9 inches. The boat weighs 375 pounds, so you need to move 375 pounds to windward 9 inches to make an 8.5ft wide platform have the same platform righting moment as a 10ft wide boat. Now on top of this we have the trapezing righting moment difference between an 8.5ft and a 10ft wide boat to make up for. This can be done with wings. The windward and leeward wings do not offset each other in righting moment. The windward wing has the full width of the boat, i.e. 8.5ft as its lever arm to hike with and the leeward wing has only the width of the wing, i.e. 18 inches to generate negative righting moment with.
Wide boats have no advantage in light winds. If anything there is a disadvantage because the wide boat is heavier. The wide boat also has to be built stronger than a narrow boat because the forces are greater on a wide boat. That is what makes the wide boat go faster in the first place. It gets more push out of the sails but only when the wind blows hard. I hope this helps.
Bill

Yes, that helps a lot. Thanks, Bill. I had been thinking that the crew weight to windward figured into changing the boat's center of gravity and, therefore, also figured into reducing heeling moment. I still don't understand why righting moment and heeling moment are not equal and opposite, but that's okay. I'll just take your word for it and have faith that it is so.

Somebody mentioned something about this thread being so incredibly long. I think it is because debates and explanations about engineering questions are like debates about sailing rules -- never ending. There's always another "but what if".

Since we're going for the record longest post anyway, let me ask what my (engineer) crew keeps asking me: Why not use titanium?
I'm assuming the answer is cost, so how much more expensive is titanium than carbon? or is there some other factor?
Al

I own two Ti road bikes [Litespeed Ultimate, Fuji/Sandvik metal works] both have carbon forks [Look] and one has Graphite Paul Lew 4quad wheels. The characteristic of both frames is the expense [L=$2400, F=$1750] as well as welding them in Argon gas environment plus they adsorb road shock. Weight wise you may save 15% or less depending on the stress loads placed on the beams/mast. The Russians have a machine makes huge wing sections for their C5A bus. They offered ti to a couple of suppliers a few years ago. They maybe approachable today if you can handle their minimum qualties.

thom

Actually I enjoy Bill's responses to the questions of those that want to know [me included] as well as those that may or may not want to debate. I hate to be a pest about asking novice questions but sometimes I fall into the its going great and I don't care why... So I look forward to when Bill takes someone to class. We all get to learn something from someone with demonstrated first hand knowledge and experience.

thom

example, headboard shackles (4000 lb working load)

steel - $20
Aluminum- $38
Titanium - $120
Carbon+ - $190

This does not really apply to cats but, it gives you relative prices.

I have used titanium on cats. I bought some and built some to replace aluminum and SS parts. The only place it showed a clear advantage over carbon or ss was sister clips or where it needed to act as a spring, it makes great sister clips.