Hey Maugan,
There is a computer program that really gets to the heart of the matter that you haven't mentioned. This is a program that takes the whole sailing system, hull shape,CB and rudder shape, sail plan, total weight, max righting moment, etc and calculates boat speed on all points of sail, generates a speed kidney. With this program you can optimize a complete boat and all of its parts. This is 1978 SuperCat technology.
Bill

Breaking the wave Barrier:
Like any design, we need to establish the parameters first. The new breed of cat has a unique requirement in that it has to operate in three modes. Typically, the mistake has been to design for displacement mode only a la slender monohull.
However, to my way of thinking the boat operates in two distinct modes and if designed for these, it will be likely that the planing mode can be encompassed too.
Below hull speed, designs are known and refined.
At hull speed, the boat is sitting in a trough, because the water has to speed up to squeeze around the boat, and because of the increase of velocity, there has to be a decrease of pressure, sigified by the lower water surface, or trough. The problem is that the trough further restricts the waters path, so it has to flow still faster....
In this mode, it is obvious that any rocker or vee to the hull is bad. (The water rushing abeam from under the hull "vee" must lower pressure and sink the boat still deeper in the trough, similarly the water flowing aft under the hull rocker, or "around" the prism)
A flat bottom and sharp edge exploits the pressure at this depth and slows spanwise flow, maintaining lift (buoyancy). What now exists is a boat that accelerates the water only around the sides of the hull, so it is bad at low speed, but not that bad.
Once hull speed is exceeded, I guess the shape of the hull needs to be more like a submarine, because it is no longer "benefiting" from the surface interface? Or perhaps in laymans terms, "the water doesnt have time to get out the way"
Before trying to develop numbers, I guess my supposition is a deep, narrow, flat bottom. The bottom in plan section would be submarine like (stretched tadpole profile), and the deck, wedge shaped (pointy end forward) I doubt there would be merit in a stern taper. I don't yet know if these shapes can mary,without excessive wetted surface,(deep hull) but it seems that the two distinct shapes will be in their mode (submerged bottom section stays effectively submerged, and wedge shaped top not contacting water after hull speed.)
Anyone out there know more about post hull speed hull design? Is it a misunderstanding on my part, or are we typically neglecting this mode?
The advent of the F14 class will force this issue, and

http://www.bowmansunion.com/portal/news/anmviewer.asp?a=1474&z=22

A mini Parlier 60 ! with wings etc . link above
A fasinating project / adventure race .

Parlier 60 ft cat link http://www.parlier.org/site02/bateau/grand_bateau.html

Interested in others comments on the 20 design version .

The diffeences between the 60 and 20 are numerous ,
most notable are hull proportion and no step in the 20 .
The radiused boards in the 20 -
Wings on the 20 -

questions on the following -

Righting system --airbag at mast top , -It would be interesting to read more about this ,--It must work in severe conditions when it is needed most .

Inflatable tent on wings --the test would be to take a firehose and hit the packed and fully rigged craft with it from all angles ,--anything not able to withstand that gets taken off or replaced .

Are added wings really needed with a 20 ft beam -
the weight and windage of these considerable -
With a 20 beam the side righting moment already exceeds anything the bows can take in downwind mode --

Wings on the Hobie 21 were very nice ,good seating , and the raised sleeping tent area concept is a good one ,-but there may be better simpler lighter ways to achieve this .

-It should be a predominantly downwind race in the tradewinds . Familiararity with a spin and handling is important , not sure about the doulble mast configuration for optimizing downwind potential . Do see a spin pole off one bow ,--
the other? -gibes etc seem time consuming switching sides .
A different rig may be considered .

The radiused boards are interesting ,-it gives 2 slot locations for them ,--one more forward ,--a tough change in high seas . Hope they pack spares aboard ,-and some rudders .

Sail reef systems --future review .

Some areas of concern , this is a prototype , so we will see revision to the design concepts as sea trials begin
It will be fasinating to watch , --wonder if they will be building additional 20s . hmmm -
Anyone up for this next year ? It would be fun to present a race challenge and start the TransAtlantic Challenge Cup .

Sponsors -needed .

Carl

Autocad has a free viewer for downloading in order to view Acad drawings for people who don't have Autocad software. The Autocad drawing is saved as a .dwf file within Autocad and can be viewed in the free Autodesk Express Viewer. Go here for the free download: http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=2952277&linkID=2475161
With the viewer you can print the drawings and the .dwf files are small so that they can easily be e-mailed. You can zoom and pan, turn layers on and off, and can tile the print if you want to puzzle a much large sheet together that your printer cannot handle.

Volo View is a more robust program that allows measuring areas and distances and can plot, as opposed to printing, the files. For lofting you would want a plotted file to use as a template. Volo View is on sale on the Autodesk website for $49. It usually costs $195.

If you can save a Pro-E file as an Autocad .dwg and then within Autocad save the .dwg as a .dwf then you could distribute the .dwf file for anyone that has downloaded the free Express Viewer.

Alternatively, I think Pro-E can save as an Adobe .pdf file but the quality is horrible. If you have Adobe Distiller you can print to Distiller for a good quality file that can be printed but it's still not as good as the features that are included in Acad Express Viewer.

If the creator of the drawings has Autocad, then the .dwf file and the free Acad Express Viewer will allow everyone to have a good look at the drawings.

What? Nobody mention Solidworks yet? I evaluated several 3d packages for our company about (yikes) 6 years ago (Pro-E, Autodesk, Solidworks, etc.) - we went with Solidworks. I'll try and put together some pictures showing the flexibility I built into several model sailboat hulls I drew up for friends.

Jake,

Ironically, I pointed out solidworks :P

Just to bring this BTTT.

I put this little drawing together during the commercial breaks of the NCSU/Vandy game (which we lost )

Took me grand total of maybe 15 minutes, and I hit a couple buttons and a plot drawing is generated for me, outlining all the dimensions, measurements and so forth. Now if you tell me that you can't design a beachcat using software like this I'm just going to call you nuts.

15 minutes people and I have an A-Frame, mounts and spring assembly. You want me to animate it?

Another update. This is after about 5 hours of work. I'm an ameteur and this stuff is incredibly simple.

http://www.ncsailing.org/ss2.gif

For any of those you that care about tilt trailers, I'll post this in the tilt trailer section too.

A friend of mine asked me to draw up a 1 meter R/C sailboat hull to his hand sketches so he could have drawings of bulkheads and eliminate the trial and error assembly process to build everything fair. This was drawing in Solidworks. Every parameter on this hull can be driven from equations...the amount of chine, the angle of the chine, the elevation of the chine, the amount and placement of rocker, the width of the top, etc, etc. All or none can be interdependent. I assume no responsibity for the design - I was doing what I was told!

Jake,

I have the axle placement equation driven as well. Right now its blank because I don't know what percentage of the total weight of a tornado lies behind the front crossbar, but its peanuts compared to the weight of the steel in the tongue. Going back to the drawing board (or sketch in sw) on the front end of the trailer. Luckily I can just redraw the dimensions and retain all the mating characteristics for the various parts.

Maughan,

As Mr. Roberts already said, "drawing" a beach cat is not the same as "designing" a beach cat. Drawing is the easy part and CAD/3D softwares certainly help - but the tough part remains calculating everything.

As an example, I've seen architecture students prepare colorful CAD drawings, with 3D views, furniture, sometimes with animated visits, etc. It is all wonderfull to see, almost artistic creations, but the drawings often represent inapropriate buildings in terms of structural soundness, thermal and sound insulation, internal distribuition, practicity, economy, etc. Those essential features require previous calculation and knowledge not provided by the drawing software.

If it is for fun, draw as many beach cats, trailers and parts to please you (as I do with my "pivoting dagger rudders" ), but common sense indicates that we should not build anything without consulting an experienced engineer beforehands.

I follow this advice even in my own profession: when we built our house, in spite of being a civil engineer and my wife being an excellent architect, we paid for other professionals to calculate and review everything prior to building. Even aesthetic aspects were reviewed by an artist. And it was worth many times the cost.

Take care,

*sigh*

I suppose that you guys wont look at it any other way. You can design a hull, rig, whatever you want from the ground up with software such as what Jake and I use. I don't care what kind of numbers you have to crunch, you can do ALL that in real time and see the effects of your design changes. I know this because I've done it before, not with beachcats but with air powered paintball markers whose precision is magnitudes greater than that of sailboats. I designed a barrel that provided the same accuracy of the name-brands but consumed 17% less gas per shot. I never even put a pen to paper, I had an idea, a basic knowledge of the dimensions involved, and I used Solidworks to come up with the design, then I think ProE to simulate the gas expansion. Am I an engineer? No... I'm a history major with a knack for thinking about things from a different perspective. All those who poo-hoo this method really irritate me. The only reason I don't show you people up and design a boat from scratch here is because I know practically nothing about aspect ratios, sail plans, or operating loads and other basic boat building knowledge.

If you want to continue to design things the "old-fashioned" way then by all means, I'm all for it, but don't tell me it can't be done as well using CAD because I KNOW it can.

"The only reason I don't show you people up and design a boat from scratch here is because I know practically nothing about aspect ratios, sail plans, or operating loads and other basic boat building knowledge."

I understand your frustration, but statements like this really show lack of maturity. Yes you can design anything strictly with cad programs i.e. FEA programs, Solids modeling etc but without any of the things you listed above you are just drawing a boat without any basis for your design. or as one would say ... your best guess. If it was as easy as you say then we wouldn't need the likes of Bill Roberts, Sabre Sails, NACRA or even Hobie Cat. Like we say in my business, if it was that easy everyone would do it. But in fact, many try but in the end they find its not as easy as they think.

JMO but hey keep on trying, the above statement does not say you can't try. Good things come from someone thinking as they say out of the box.

Clayton

Being a mechanical and electrical engineer, I can understand the benefits and challenges associated wtih desiging a boat starting with numbers and theory. However, what I can't seem to grasp, is why you guys keep pooping on the backyard builder that wants to design a hull that starts with being pleasing to the eye and the builder's ideas. All that this thread was about was some folks getting together to exchange ideas, learn a little on the way, and maybe build a boat. Our world would be a worse place if it weren't for the back yard builders who are desiging from an alternative perspective to the extremely technical one. Did Hobie Sr. know everything about the proper relationships between the speed and hull length ratios and the prismatic coefficient when the first Hobie 14 was built? (I really don't know the answer to that but I suspect it's "no" ).

All of the above (except perhaps sabre, whose history I'm not familiar with) were conceived before the advent of the design methodolgy that I'm advocating.

Do you think Ford uses the same methods to design cars that Henry used back in 1903? I'm sure they share basic design strategies but the difference is in the tools available today.

Find another argument please.

"My hull design is so much better because I used an abacus to compute the curve of the chine!!"

I worked at Ford when they started using FEA and computer modelling to help with their designs. One of the things we found is that knowing the tools (CAD, FEA, etc.) didn't guarantee better design. If the tools weren't used in conjunction with sound engineering principles, they would often mislead you. "Garbage in, garbage out." This was really evident in some of the early FEA work. Ford still spend huge amounts of money testing prototypes and Design Verification and Proveout. We all continue to get better but there were some real setbacks when "computer based tools experts" produced some designs that failed miserably. Some of Ford's management was ready to throw out the tools. Thankfully, the engineers recognized the value of the tools when combined with real engineering expertise. The best tools speed up the process. The best designs are based on good physics and engineering knowledge.

I'm not discounting the value of engineering expertise. This is why I just don't turn out a boat right now like I stated before.

I didn't have the patience to deal with the egos of the engineers in college :P

Good advice Luiz -

interesting Irens design -
S-Cat http://www.nigelirens.demon.co.uk/scat.gif


The T foils seem suceptable to damage , but look great ,

Have any yet tryed paralell dual boards with T foils attached-- {provides two points of attachment for the base foil}- --contained within a more rectangular canted hull shape -setting the T foils on the cant towards the sail plan C E and each other on a catamaran .

They could retract but only to the hull bottom ,--unless this was combined with the similar seaplane type hull shape with the step up in the hull ,--the T foil could retract into that area ,but still have some extended side area projecting .
Or alternately a narrow displ. hull design with step area for retractable foils --a deeper bow and stern area than center hull section .
Might be an area of design pursuit .

It is a publicly known fact that he did not know any of those things and had to re-make parts of the boat many times before it could sail. This explains why the Hobie remains a poor design from many points of view. Its success was based on other marketing qualities.

But don't get me wrong, I like to play with shapes, ideas and new concepts and there is nothing wrong with trial and error. It's just that not all people have the resources, patience and risk apetite to build things (boats) using this method. It may be funny, pleasant or even poetic - but it is not safe or efficient.

Cheers,

I've seen a continuous curved foil from each float to the other somewhere in the web. It seems to me that the foil results too large and draggy, if the boat is wide enough.

The Scat is basically a big Rave. I read in Multihulls Magazine that its top speed so far has been under 30 kt, but this must be a misprint (maybe under 40 kt?), because the Catri aready sailed faster then 30 kt.

Cheers,
Luiz