flat vs convex surfaces

*With automated welding machines, the skill level is less than it used to be. Also, they are methods to pre-shape the pieces, which don't necessarilly need to be small and become a multitude. An example would be a rolled chine hull. The sides and bottom panels of a chine hull can be made in one pice. However, you should accept that if a customer wants a particular shape, and is willing to pay for it, the customer will get his wish; regardless of difficulty or skilled labor requirements. There are plenty of designs for home builders that use simpler methods if you don't have the appropriate skills for a more difficult build.

 

I understand that rich customers can ask any curves they want and that poor self builders better choose more simple boats.
My question is more geared towards the next steps in the industrialization of the production of "+40 foot cruising cats".
Gonzo, you bring in that rolled chine hulls allow for larger pieces. Welding larger pieces is already introduced in the latest Mumby/Oddysea design. But this does not seem to have a large effect on the scantlings and fitting these large pieces do need longer time for the right adjustments.
To reduce the cost of building "production" aluminum cats, Vietnam Navy defense contractors offer their facilities and skilled labor. Since the building of their first Mumby/Oddysea there, they seem to have a dozen or so cats in production within the shortest time frame. There is a market out there.

Is there a form that is cheaper to build that covers enough of the functions that the cruising cat market expects? I thought that "squaring" the typical cat body design would have a more relevant impact on building and outfitting labor costs. There is already a unmistaken trend towards less curvy designs and these are still stylish enough to attract customers. Are these not having an effect on reducing production costs? Is there a form that takes this trend to the more extreme (without worrying at this point about what esthetics are popular enough) to have a relevant effect?

To summarize the results of the discussion in this thread: contenders for more extreme flat designs are deep V, polyfaceted, and transonic hull variants. But there is serious professional skepticism about their potential to reduce production costs significantly. I remain disappointed but enlightened. Thank you all.

 

There isn't much of a market for new boats that are not aesthetically pleasing, unless you are referring to poor areas in the world where anything that floats will be acceptable. In those areas welded aluminum catamarans are not an option though. The hull is probably 10-15% of the cost of the total build. If you were to save 1/3 of the labor and reduce the total cost by 3-5% but result in a boat that is not marketable, what advantage can you find?

 

For sure, Gonzo.

Separation of concern does not mean not treating the concerns. Esthetics may be a concern. Sometimes, to some of the public, a very different design can be even more appealing. Case in point: the Cybertruck. Often there are also ways to add simple make-up or trompe l'oeil tricks to soften shapes to gestalts that are more appealing to a larger public. But that is a matter more for consumer product designers. The french designer, Starck's role in designing the late Apple owner's yacht comes to mind but that is of a very different category all together.

The breakdown for the proportions of costs of building a hull versus total costs of a boat are ball park figures for current designs. I would argue to also count on the important trickle effect of squaring in a design, where the labor savings are accumulating further with those for fitting out a more simple interior shape, like the more straight (forward) installations of tubes, wires, cabinets, doors, et al. If flat saves 3-5% of total boat costs in the hull alone, flat may save the same proportion of the remainder that is 85-90% of the total boat costs, ranging the total saving between 18-30%.

Consider for example, to have the inside dimensions in multiples of Eurobox standards. This opens up the "cabinetry" to a wealth of off the shelf (pun intended) industrial boxy products for storage but also including built-in washbasins, toilets, cook tops and the like, all ready to fit stacked up or next to each other with a wide choice of fasteners, holders, bottom plates, lids, ...

 

To remove compound curves from boat design is
akin to removing colours from paint, or carbon from steel,
or moisture from water.
I think the whole idea contemptuous.

 

from an engineering point of view?

 

From the common sense point of view.

 

I am also often surprised common sense is not as common as imagined. Perhaps I should have picked up earlier that I was outstaying my welcome. Nevertheless, I am grateful for the patience you have shown in this thread.

 

I think the conversation has been extremely valuable. The question has merit as the starting point. Examining engineering design principles isn't a waste of time.

 

Agreed

 

You haven't "outstayed your welcome", it's just that "squaring" doesn't bring anything to the table. The robots don't care if they cut or weld straight lines, curves or at any angle.
For hull construction cheaper robots with limited motion range can't reach all places to be welded, and they only make sense in an old school fixed model assembly line situation, modern automation has already moved on, the future belongs to units that are not bolted to the factory floor. Someday they will enter boatbuilding, but for now the capital expense is too great for smaller builders.
You have to consider that even the automobile industry hasn't yet achieved a "lights out" factory, and not for lack of trying.

What you should do is use youtube to visit some factories and boatyards to see what's already beeing done and how. Designing for production technology starts with knowing what can be done in practice today or tomorrow. To give you a simple example, on high production GRP boats half of the interior is molded directly into the hull liner, compound curves don't matter. Wood furniture is designed to be cut on normal 3 axis cnc's, curved elements are bent from sheet or carved from solid stock via big molders and glued in. Entire units are pre-assembled and installed into the hulls in a single operation.

 

I did come here from watching youtubes on the construction of Danish Dragonfly, Outremer, Seawind, HH, Rapido, Woods, Kohler, Harryproa, Mumby, the Delos alum cat, the kit cat of MJ sailing and Schionning, and others and HDPE curved pilot boats and no-curve barges. None are automated and most have emigrated to cheaper labor countries if not DIY. I find it hard to believe that squaring designs does not simplify production (except for 3D printing).

So, the thinking is how much curve does one really really need?

If windage is determined by surface to the wind and aerodynamics, then faceted bodies above the waterline may not be as prohibitive on second look. There are also turbulators, tabs and dibs and the like that "fool" the airflow around hard edges.
For pounding through waves I notice the lack of most curves in high speed stabilized monohulls. I learned here about the all flat faced transonic hull.
To the naive onlooker that I am, it looks tempting to build multihulls almost as simple as welding compartmentalized fluids tank boxes in HDPE.

So, how much strength inherent to curves must be compensated for, resulting in a heavier built for flat designs? If a sphere is about 24% stronger than a cube of the same volume (correct?), the penalty in comparison with an average curved cat may be speculated to be about 10% or so. This may be compensated by a ballpark of more than 20% savings in cost of ownership (production and maintenance) Quod erat demonstrandum.

 

In the delos video, they spend a significant percent of the hull time in bending and fitting the plates. A faceted design would probably have removed about 30% of the labor to date.

 

Designing a hull with curves ( and I am talking about engineering design, as compared to a sketch of a shape that may or not work) can reduce weight but your "how much" question
is impossible to give you a number off the cuff. In your first post your comment was "responders will come back with ""it depends". And it does

Properly designed, you could (oops) a Naval Architect could almost produce a monoque set of hulls with minimal frames to save weight.

A square transom sketch that you provided in one of your posts negates pressure recovery from the midpoint back on a symetrical hull. (transonic)
Ie ahead of the midpoint of a smooth long curve, there is a higher pressure distribution. If you have a curve toward the back, the water provide pressure against the hull from the midpoint back provides a pressure recovery. Fast fish have a long taper to the back, a 747 with a large front section ie lots of air to displace, recovers pressure to the tail.
So pointed in the front and tapered to the back would be the best shape. Rob Denney's post 51 appears to be made with developable surfaces. Minimal welds. The upper chamfer can easily
be made without expensive rolling equipment by inserting say a 2 inch pipe and just hand bending this into a minimal amount of frames and attaching the deck and sides.

 

No doubt, but if the aviation industry is a guide, it comes with higher cost of materials and skilled labor.

I am happy you bring this up because, again from aerodynamics, this is quite surprising. But the transonic hull was designed by an aeronautical engineer, discussed among NA's, built and tested as models in tanks and in seaway. There is also a short paragraph in one of the papers explaining its role in virtually lengthening the effective waterline length. Also in the proa application the hull would consists of two transonic bows end-to-end symmetrical in the transverse plane. Just reasoning behind the desk, this should work. To be tank tested, of course.

I don't think I have ever had a suggestion that Rob has not tried, one way or another. Who knew about his faceted hull design try? His building experiments are as frugal as can be, some call them cheap in the pejorative sense, others ,costly in the end. Bending flat infusions into submission like in one of his "intelligent infusion" youtubes illustrate his state of the art.

And one of these dependencies with potentially major impact is how much curve is really necessary within the relevant range of Froude numbers within which +40 foot cruising catamarans operate? Pushing the limits in hull shapes is at least or only a probe into the elasticity of design envelopes.