dory catamaran hull

is approximately 10,000 pounds too heavy for a powercat format you were seeking? 40 ft loa approximately and better than 100 kmh? cruise... http://www.boatdesign.net/gallery/showphoto.php/photo/15578/ppuser/22903

 

This is thread drift again, of course, but I'll point out that some of us feel we have little choice but to attempt originality, since we're smart enough to know that we're not going to beat Morelli and Melvin at their own game.

In my own case, I'd find attempting a modest variation on a well-established kind of boat to be pretty uninteresting-- so much so that I doubt I'd ever finish.

In fact, the only reason I attempted to design a boat in the first place was that I wanted a type of boat that didn't yet exist. The process turned out to be pleasurable, but it wouldn't have been nearly as much fun if the end product was a cookie-cutter boat. Of course, had the design been a failure, that might have taken a lot of the joy out of it. But I had a fallback plan. If Slider had been a dog as a sailboat, I was going to put an outboard and a canopy on her and go fishing.

Someone once famously said that the price of speed is accidents-- in reference to racing yachts. In a similar sense, the price of originality is failure. If you attempt originality, you are much less likely to produce a successful boat than the designer who does not stray from the path of conventional wisdom. Even so, I don't really understand the appeal of the latter approach.

Maybe it's because I'm too old to envision a career as a designer, so I'm just doing this for my own amusement. No matter how nice a wheel might be, reinventing it just doesn't sound like much fun.

 

But there is a difference between a rectangular cross-section with hard chines and a same section with rounded, or soft chines.
Since you say that we have to look into first principles, will you at least agree to the fact that a square chine will necessarily produce an additional drag due to vorticity production and an additional lift - when at positive trim to the waterflow? That is what I am saying. If you disagree with that, then can you please explain why do you think it doesn't happens, based on the first principles?
In your post #26 you had shown a picture of a new US Navy ship. It does have a rectangular cross sections but it doesn't have hard chines. They have been all rounded and faired, and not just for structural reasons.

 

This hard vs soft chine issue is a vexing one. Construction considerations favour a hard chine if the boat is built from flat panels but the soft chine is favoured when the hull is primarliy a molded skin.

There is a transition between displacement and planing modes, a power boat has adequate and consistent power to bull through the transition but a sailboat is subject to the vagaries of the weather.

 

For those that are tired of hearing the arguments, here's some hard data on power catamaran hull shapes:
http://www.multihullsmag.com/magazine/articles/cathulls/cat hulls.htm

 

It looks to me as though the dory form is completely valid. There are may fine designs out there using it . Richard Woods GYPSY28 is a fine example of the sailing type and I see no reason why a dory cat would not make a fine power boat. I think much of this come down to the material being used for building , and of course cost. If simplicity and cost are of no concern then other designs make more sense . Commercial considerations would dictate that it appeal to the mostly ill informed consumer .

 

Gary,

Is there any data on flat bottomed dory-esque hulls to accompany that link. I saw rounded forms, foil assisted forms, split mono forms, a variable deadrise form, but no flat bottomed form of the type we have been discussing.

 

Rick, technical merit does come into the consideration, without a doubt. There is something going on here within boat design, though, that takes the process well beyond the business of simply getting it right technically.

Boat design is just that... design. Design is a complex subject that encompasses all of the technical applications of the product AND it's aesthetic potential. It's not one, or the other, but both. We've all seen boats that meet all the technical requirements and when you look at them they come up well short of being pleasing aesthetically. Conversely, we have also seen pure art expressions that were just about helpless out on the water.

It's that two sides of the brain thing come home to roost in the portfolios of all boat designers. It was for that component of the argument that I brought forward the example of the Porsche Cayman S. That vehicle is absolutely loaded with all the state of the art engineered solutions one could ask for AND it is all contained in one of the most aesthetically pleasing forms within the automotive marketplace. A form that, at once, comes to grips with the aerodynamic needs of a high speed vehicle and also translates pure flowing, organic correctness to the business of fulfilling the eye and the mind of the beholder.

The whole package is the objective here and not a one sided solution which forces the other half of the brain to revolt.

It's true, I am not an engineer by trade. I was brought up with a deep immersion in design instruction, a lifelong profession as a photographer/cinema cameraman and an education at one of the best film schools on the planet. I naturally seek aesthetically designed solutions that allow the owner/builders mind to wander over the form, imagining himself in a place that not only works properly, but feels good to own and operate.

I have had to learn the engineering craft in order to meet the basic responsibilities of my design work in the field. Any engineered solutions beyond what I know, I seek out the skills of someone who practices in the field and incorporate their advice within the design. I consider this to be practical, as well as professional. Very few in the trade have been blessed with a gift in both sides of their brains. There are some out there and I deeply admire their work. I'm still in training with the more complex engineering aspects and it is a lot of fun to have a learning process in that fashion at my age.

I wonder, though, just how many engineering oriented designers seek-out the input of a talented designer with strong artistic skills so that their work can be that much better?

 

Personally I think the Porsche is a useless car for my purposes.

All I want is a steel box on wheels that will take me safely from A to B. Oh, it must also be able to take a 220kg/400lb drum of resin in the back and allow me to sleep in it when required.

Seems to me that too many designers look for glamour and not the practicality that most people really want

I get the impression from garydierking's link that the author of that article was the designer of the last two hull forms. If so then it wasn't really an unbiased article, so couldn't be considered to be giving true "hard data".

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Yes, it was an opinion piece, though the author probably knows a whole lot about power cats.

I did notice that one of the categories in which he rated the hull forms was "Economy at planing speeds." If the boat Frank is talking about is meant to power at 12 knots, wouldn't a displacement hull be better than a planing hull?

 

know your subject

I have to chime in. Chris, I don't know very much about boat design- just from experience, but I do know about current car design. Look at a current Porsche RACE car and you will see what really works in the wind tunnel, on the track, and with a good program on the computer- and there is hardly a curve on them. Street cars like the Boxter are designed to be "pretty", with as low of drag as possible and not offend the sales staff and customers. Bolger, a designer that I respect because he was not afraid to experiment, designed several power boats with a flat "shoe" down the middle that does work- hard edges and all, and there are planing dorys built on both coasts that are known for their low power needs. The flat bottomed Bolgers, planing on their "shoe", look a lot like a flat bottomed dory would to the water and have really low power needs for the weight carried. A 10' round tube inflatable planes far quicker and goes faster with a 6" strip of plywood under each tube fore and aft. I tried it on mine, so they do work on a cat. They are really noisy , which might be a reason production builders would not go there, and the flat surfaces work best with plywood, not production friendly either. Bruce

 

I'm sorry, Bruce, but I fail to see your argument as to, "hardly a curve on them", when you wish to form an argument relative to the Porsche RS Spyder RACE car. The widths of the cars are limited by class rules, so yes, the sides of the vehicle are, more, or less, planar surfaces. Even then, the side of the car as it exists the front suspension point, is decidedly curved. The rest of the car...? Go ahead point out the meaningful planar surfaces that are not curved when compared to the entire vehicle's form. Shown below are the RS Spyder and the racing GT3 Carrera in various livery.

Bruce, race cars do not survice the rugged crucible of serious competition with flat surfaces all over the place. Go back and look for a non-organic racing vehicle, see how it did and then tell us what kind of shape supplanted the flat surfaced form.

The cars shown below are examples of the class winning vehicles that were just racing this past weekend at the Long Beach Grand Prix. Perhaps you have something more current?

 

Hmmm, I am a bit confused now. Are we talking about displacement or planing hulls in this thread?

 

I see your interest, Richard. I have a '92 Toyota Landcruiser which I have owned since new and other than being a gas pig on the highway, it just runs and runs and runs with only an alternator replacement since first purchased. It carries just about anything I need to load either into it, or onto it and if that doesn't work, I haul a trailer. That part of the argument is understood. .

Still, I am looking to complete an ongoing restoration of a '62 Porsche and enjoy a real driver's car on weekends with my wife. The Landcruiser doesn't come close to that experience.

I also understand the function of plywood build techniques when it comes to easily crafted boats for the builder who is not as accomplished. I likewise understand the practicality argument... but that does not mean that a boat has to be grossly ugly while achieving same.

What we do when we buy into the simple and ugly format is to say that mediocre styling is just fine with our sensibilities. We might as well wear the same kind of impersonal clothes, have a similar, plain and ugly home... never ask our kids to comb their hair before going to school, never honor the request of a daughter that wants to look nice for a dance, and on and on we go until we succumb, completely, to the vast blandness of mediocre everything in our lives. Kinda like that argument that was being pressed by the now deceased Communism of the Soviet Union and the former artifact of The People's Republic of China... both now non-functional in their collective, anti-styled behavior.

I wonder, how many of us would be willing to board a mediocre styled aircraft bound for a trans-Atlantic destination and call it all good since hey, we're simply mediocre beings with no expectations of the finer things available? To my way of thinking, that's an airline destined for failure in more ways than one.

I suppose that one could get away with poorly styled dishes and flatware, though I think that, somehow, the lady in your life would object. (Maybe that's why some of us don't have a fine lady in our lives?) Same would be true for the curtains in one's home, the furnishings and the rest of the stuff that fills one's life.

This anti-styled thing goes nowhere with me when the stuff that surrounds one's life can just as easily be thoughtfully designed, while also providing all the serviceability, if not more, as the Plain Jane version.

I'm waiting, now, for the arguments in which our fellow members say, out loud, that they aren't worth having something nicer in their lives when they can get bone-jarring, plywood simple and call it good enough.

 

This started as an interesting thread with a fairly practical goal. I've been lurking sporadically but haven't had much to add of value. Two points have come up that spark comment.

I'm not buying the smooth river rock school of hydrodynamics. Water doesn't shape stone for optimum flow. The smooth shape is a function of differing degrees of hardness and grain structure of the stone and initial surface shapes. Edges concentrate wear, edges wear away first. This has little to do with optimization of shape.

Second, many of the exotic racing teams do have the budgets and desire to do the research to optimise thier cars. They test intuitive, empirical, and theoretical ideas constantly. Some teams are testing and tuning through out the entire year.

It would be interesting to see this thread bear fruit within it's original parameters. Carry on.

PS that toyota will come in handy for towing the porsche home. I had a 67 for a short time as a young man. It may not prove to be as reliable as the old landcruiser.