Catamaran Cross-deck Design

I think I know what you are asking: both design approaches can be made to work, I think what you want to know is, the integral hull frames and beams will have fewer parts, weigh less and take less labor to build. the reason why you would not use this construction on all hulls is if there was a reason to make it so the deck and hulls can be separated for transport or heavy maintenance, you need connections between the beams and the hull frames that can be unbolted. Sometimes it is a very desirable feature to be able to dismantle the hulls and decks and be able to ship it in a shipping container back home, it actually is cheaper than sailing it back at the end of your trip. so you save money on long voyages to have family and crew fly home and have the yacht shipped home, rather than pay a professional crew to bring it back.

Also, on large vessels you may not have a big enough facility to build it in one piece, or your facilities are too far from the water to transport the finished hull over land. So the final assembly is done out side, or next to the launch point.

It is also possible you do not have a large enough Numeric Control mill to make the frames in one piece, so you make them in sections that can be assembled. so it could actually save overall costs, by spending more labor on assembly to use smaller, less costly equipment and facilities you have at hand, rather than to contract out the cutting out of very large one piece integral frames.

If the boat will never expected to be disassembled, than you ideally would build it lighter and with fewer parts to achieve the same strength. Fewer parts also means lower maintenance as far as corrosion.

 

Thank you, Petros, that's what I want to know, exactly. Here, I don't think that good Numeric Control services would be available, that's why I've been wondering how these frames are produced. But, there's another question yet in my mind about these types of frames. How can one design these CNC-cut frames? I refer to ABS guides for constructing High Speed Craft. And, using it, one can calculate various scantlings for side frame, bottom frame, deck frame and the brackets. I want to know if the design procedure for these integral hull frames (& beams) is the same? I hope you'd understand what I mean if you looked at the attached sketch.

 

Thank you all the others, too, who have been answering to my question. I was away from internet during the past days, and couldn't reach to your replies, I'm sorry. And, Zulu40, thank you, I'm interested in your self-supporting-deck concept. Where can I find more details about that?

 

not sure of your question, the design process is the same: you determine loads on the smallest elements of each componet, I like ding a "free body diagram" of each component. Than you build the load path to to the gross structure. Each connection has to be examined for capacity, if you are building it in one peice it is the same, but you have to examine each part of the design for capacity.

You do not need a big CNC machine, they can be laid out, and cut out by hand. But that is very labor intensive and handling the larger parts is more difficult.

The aircraft industry went through a similar change, the older Boeing 272, 737, and 747 has frames and bulk heads built up from smaller parts, but the later designs like the 777 and 787 use CNC cut one piece bulkheads and frames. the design change was improvements in manufacturing technology, not so much in loads analysand.

 

The calculation procedure is exactly the same in both cases.
The right model can have lower cost in labor but you have to take into account the cost of cnc machine and wasted material, which will be higher than in the model on the left.

 

Although many designs are worked out on the basis of what is already known to work, where it is the experience with thicknesses of foam and fibreglass, or aluminium plate and intercoastals in previously successful designs that will contribute to some future vessel. Few amateurs are capable of designing a boat from the ground up without some residual guidance as the crucial knowledge about the forces and stresses involved is unavailable or unknown to them. Unless an intended design is very close to an existing product amateurs would be best directed to a reputable designer.

While there are fewer examples of self-supporting decks around they are actually easier to work out as opposed to more common monocoque boats being of simpler double cantilevers of usually uniform thickness. Easier still if they're powercat designs as the inherent stresses caused by having a mast and sailing rig are absent. So you would be looking for a designer that has produced similar examples of this sort of theory before, which is why I got into the conversation about trimarans which offer for the most part a close likeness.

Likewise if you were getting into this because you had a dislike of producing moulds jigs and framing you dont think would be used in the final design you would be looking for someone who also has demonstrated some talent in that area too. That said designers come with their own suite of ideas and way of working that needs to be respected. But before you choose to contract a designer you need to be more cognisant of what your actual needs are and what your budget is. This will be less about what a boat looks like and more like the fundamentals at hand and skill set you have.

 

Yes, exactly the same. The only difference being how each is constructed - a production issue.