Modular Cruising Catamaran

[yipster]

here attached a rough idea for a triangular cat framing spaceframe, could be modular too i guess
any thoughts on it? any reason why frames are not used triangular or sawtooth wise?

[marshmat]

Yipster,
I see no reason to reject a spaceframe as a possible solution for a cat.
I think the main reasons we don't see them often is that it is very difficult to design a spaceframe that doesn't intrude into the living spaces. Structurally, it is a perfectly sound concept.

I.N.,

The idea behind the "design spiral" is that, with each analysis of the idea and subsequent revision, you get closer and closer to what you want, making ever-smaller changes, working on more intricate details, until you have something that meets the requirements you set out for it.

At this point, we're still fairly early in your design spiral. Although it's certainly a good idea at this point to do a few back-of-the-envelope calculations to get a rough idea of the structural challenges involved, the detailed design of the structure simply can't be done until the general arrangement of the design has been decided on.

That's not to say that you shouldn't be considering structural issues, seeing as this will be one of the main challenges with a transportable, inland-buildable boat designed for modular assembly. But for the moment, I'd look at it in terms of "where are these stresses going to go", rather than "how big does this beam need to be"- a question which is impossible to answer now, but relatively straightforward once the layout, geometry and weights are known.

The freestanding vs. stayed mast is a case in point. Both are possible and feasible, but the engineering concept is very different in each case. One needs to handle huge compression loads on the mast step, the other has to resolve huge bending moments. The decision should be made based on the performance and handling characteristics you want. Then- and only then- the engineering should be done to satisfy those desired characteristics.

Of course, at some point we will also have to think about the hull shape itself. Perhaps that is a subject for another thread, though, leaving this thread for discussions on the modularity idea.

I've been tossing around some ideas for a year or so now about an inland-buildable, ocean-going cat of 50' or so. I'm convinced that there do not need to be any compromises in strength or performance to facilitate modular inland building and near-water final assembly. Any such project for me is still a decade or two away, but I'm following this thread with interest to see how this works out.

[Ad Hoc]

Matt

You pretty much summed up my last, but rather more, succinct reply, thanks.

[yipster]

Originally Posted by marshmat

Yipster,
I see no reason to reject a spaceframe as a possible solution for a cat.
I think the main reasons we don't see them often is that it is very difficult to design a spaceframe that doesn't intrude into the living spaces. Structurally, it is a perfectly sound concept.

thanks for the reply mat, finding the right web and 3d path's is indeed intricate
maybe that projection thing is the reason behind square, instaed of zigzag framing as well

[ImaginaryNumber]

Thank you, Ad Hoc and marshmat, for helping me to better understand the design process. I definitely want some variant of a junk rig, so that requires a free-standing mast. Of the five catamarans that I'm aware of which use a junk rig or a junk-rig-like sail, all are bi-masted. I'm not partial to bi-masts, just going with what others have apparently found works for them.

I'd encourage any others who are following this thread who are particularly interested in the modularity concept to make your interests known. If there are many potential catamaran builders who are interested in a build-it-inland cat, it may encourage the professional designers on this forum to consider this style of design a commercial opportunity.

Looking forward to learning more,
i

[rayaldridge]

The well-known designer, Tom Colvin, uses stayed masts on his junk rigs, so unstayed masts are not a hard-and-fast requirement for the rig.

Chris White, who is probably one of the best multihull designers now working, tried unstayed masts on his 60 foot tri Juniper. He recounts his experience in his book, which I recommend. In brief, after several years, he replaced the rig with a stayed rig. He found that he was unable to adequately control sail shape in heavy air.

Bear in mind that unstayed masts for a cat must have much heavier scantlings than the equivalent sized rig for a monohull, because of the enormous initial stability of the cat.

[Ad Hoc]

I.N.

"...Looking forward to learning more,.."

If you wish to learn more, perhaps you should ask all those who think they know better and whom have never designed anything for their advice, since they think they are such experts, but of course making a comment leaves one open to scrutiny. Hey great idea, lets see what words of wisdom these "anonymous" posters come out with....surely they must be able to contribute, otherwise how would they know a good comment from a bad one to hit neg points??...

[rayaldridge]

Originally Posted by yipster

do have respect to knowlegde but slightly uncertain if spoken to as adhoc generalizes "I see the uneducated, immature and ignorant are out again"
i'm just an amatuer too and get doubts over mentioned spaceframe, sure plating and framing goes together, space and zigzag frames no good?

Yipster, I don't think he was talking about you.

I think I've seen space frames, or at least triangulated reinforcements, used on racing multis, though I don't remember the details.

[Richard Woods]

I agree with others that your design spiral is getting really skewed. You don't need to think about the structure for a long time yet. And it is curious, to me at least, that you haven't yet published an outline accommodation or deck layout for discussion.

On space frames. Remember the Bugatti "bird cage" racing cars of the 1950's? Later used as a concept by IOR boats "The skin just keeps the water out, bulkheads and frames provide the strength"

Both quickly supeceded by monocoque construction.

Speaking as one who has personally taken a 20ft wide catamaran down a 14ft wide Cornish country road and who has designed modular boats, like the Gypsy for example - one of which was built in three different countries!!! I still think you'll find that you don't really need to follow the route you are taking.

Having said that, have you considered making the complete central section of the boat and adding bows and sterns to it?? So you'd have an accommodation block 10ft 6in (say) wide (on the trailer, obviously 10ft 6in long on the boat) by 20ft long (or 20ft beam on the boat).

I am guessing that 10ft 6in is the max trailing width you are planning on, but different countries have different regulations. In the UK the max legal trailer width is 7ft 6in, but you can have an load that overhangs 12in each side, so you can tow 9ft 6in without a police escort. You can tow up to 14ft wide and 16ft high (I think) with a free police escort. Bigger loads than that are feasible, but I believe they require that the Queen walks in front carrying a red flag.

Richard Woods of Woods Designs

www.sailingcatamarans.com

PS thank you masalai for the note on reputations and where to find comments. Like yipster I'd always wondered what "rep" meant.

[downunder]

Dereck Kessal has several modular designs and is desining most of his range now for modular construction - the < ma range> in 3 sections 2 hulls and bridgedeck. he is currently in the USA according to his website

http://www.kelsall.com/sailcat.htm


http://www.kelsall.com/kisskat/index.html

[marshmat]

Not sure what it's like in other jurisdictions, but around here an oversize load permit for up to around 10' wide is just a matter of a few hours and a few dollars. It's when you start to get into over-height, or seriously over-wide, that costs start to skyrocket- calling the utility to temporarily prop up overhead wires, that sort of thing.

[rattus]

Richard, the "birdcage" cars were Maseratis; the original's complexity appears to be somewhat greater than what Yipster had envisioned ;-) : (nice model of the chassis)

http://www.classicdriver.com/uk/maga...0.asp?id=12506

John Shuttleworth also did an interesting analysis of a spaceframe bulkhead engineered for the loads of an Aerorig:

http://www.john-shuttleworth.com/Art...eroDesign.html

See Figure 10 for the spaceframe detail. Interesting stuff!

Mike

[masalai]

Royal and Yipster, nothing directed at you folk, It is the usual bunfight that erupts when some ignoramus feels his bluff has been called and the only recourse is a petulant childish attempt to get even by anonymously giving negative rep points.... It is just a wankers' need to be told every so often to sit quietly in a corner, take their meds and see their shrink/counsellor...

I am sure it would all be resolved if negative rep was disabled and / or ALL who give any "rep points", was identified.... - such is life -

[Ad Hoc]

"...I am sure it would all be resolved if negative rep was disabled and / or ALL who give any "rep points", was identified...."

Fully concur

[yipster]

yah, no way to use that spanner also from japan and i for one promise to try to use the rep's in a good manner

thanks for all the ideas on modular spaceframes and for a one off i was thinking its easy'r than a splitted monocoque
with foam sandwich the water can be kept out and enables working bigger skin sizes