3D CAD models of beachcat hulls

Thanks carlm

Think your saying CAD systems are just a design tool .

Most understand intuitively design aspects ,-Hobie shaped surfboards then devoloped the H-14 then 16 ,then 18 etc ,
each improved with knowledge gained . The 16 not really a great racing design ,--a classic Tornado- it is not ,
It is a great simple durable popular non boarded beach cat .

The concepts most understand, and the basics of design , I,m just an amateur cat designer ,just a fun hobby ,-weak on the actual applied engineering and calcs and would seek out Bill or an equally skilled experienced designer for plan review and recommendations before starting a project. Often do this with residencial design consulting with soil engineering firms ,-structural engineers ,-civil engineering firms on survey and zoning issues and site elevation planning , topos and site development and planning , local ZBAs & Twp engineering firm ,-truss engineers ,-TJI joist systems ,--panelized homes and panels ,steel engineering data ,beam spans etc ,--environmental engineering ,-advantec fields etc --precast conc engineering firms etc etc .
Always listen and follow their direction.

Sorry about the hurried posts and numerous typos , hope they can be deciphered --

Interested in building a Formula 14 or 16 with my boys ,
the F-14s have very open rules -L 14.3 B unlimited W no min
sail ar. 300 total in any config.

Two choises are available , either an existing production 14 that inc -Mystere 4.3 http://www.cat-alist.com/headlines/mystere4_3.htm
nice looking 14 ft,cat w spin
a Hobie 14 w hooter -

Trac 14 - http://www.geocities.com/cctexan99/trac/photos/
N 450 http://www.sail4u.be/nacra_450.htm
and several other good 14 ft production boats , or the option of taking a number of great looking 15 ft boats and reducing L to 14.3 -- The problem with production boats is they all weigh from 240 to 300 Lbs ,-though 300 sq ft of sail on a 14 L will help offset that , --but a 14 ht type const , or fold up plywd home built will weigh as little as 107 Lb with same sail ar.
120 plus Lbs on a 14 L is a much greater percentage of total and much larger factor , so -the F-14 class will need two categories in the near future --An ht lightweight boat category ,-and a production boat category with min boat weight of 240 or so ,

For any thinking of home building a project check out Phill,s excellent web site ,-one of he most helpfull nicest people around .
http://www.geocities.com/Phillbrander/

Some nice 14 projects shown -

A main concern in designing a F-14 or modifying an existing plan to add a spin and added loads and sail forces from it are getting enough volume in a 14 ft L to support boat crew weight plus sail forces particularly downwind where there is only 6 or 7 ft of hull Length from the mast base to the bow. -Moments and pitching are a much greater concern than the 25 ft L C class hull with its main goal of reducing surface area . A scaled down C would {as Bill noted}- would not have enough volume , and would pitch and hobby horse terribley , and would pitchpole very easily -

Designing in more proportional volume ---
One experience I had with a very old design cat called a Pheonix with very wide buoyant hulls that I restored was its poor characteristics when it heeled or flew a hull.
It was very wide and deep in section just forward of the crossbeam with narrow bow and shallow stern . As it heeled up,- one hull skimming in typical mode,- the wide large volume mid area hull would , due to its wide center area and change of heeled underwater shape would pivot around its buoyant center sections and nose dive in a bow down attitude . Not a good design feature for any cat .

Actual sailing modes and heeling angles are important considerations , calc of sail forces , crew weight on the wire, righting moments , stability , how the design will respond under a wide variety of sailing conditions seas ,winspeeds ,crew weights , mast height sail area variations , balance CE clr -it is a wonderfull intricate engineering art form of sorts.

Canted hulls are an interesting aspect of cat design ,
They present a more complex interplay between heel angles and allignment of the two hulls under sailing conditions or in more bow down attitudes and hull submersion from sail forces with hull up or two in during mid and lighter wind conditions.

The F-14 design project hulls will need to be fuller ended , wider per scale with a larger hull beam to L ratio to provide sufficient volume. The unlimited beam is an interesting aspect , with proportional bow volume area required from the additional crew righting moment might lead to a very wide bow section design and an attempt at a planning type hull shape in that size range.
Planning sail design requires wide flat bow sections .
http://www.whbs.demon.co.uk/sr2/content_fr.htm

The other option of a F-14 sized production boat modified would be a fun project also , The Mystere uses a Dart like hull configuration with molded in fin skeg -keel ,this addes some volume as well and makes the balance under spin asier a does the N 450.

All types of sail plan configurations are possible on any F-14 , hope we see some interesting fun innovation.

Dear God here we go again.

Bill: You obviously misunderstood what I was saying. While its entirely possible to, what you're saying, scale down an existing boat to 14 feet and just axe all the dimensions by the same proportions, thats not the extent of the capabilities of CAD software. If any of you think thats what engineers use it for, please...

I'm not "taking a shot" at BR either. Don't put words in my mouth.

I apologize to all those are still using slide rules and arquebuses. There is a better mouse trap.

Hi again,

I was just curious what your background is? At least regarding the extent of CAD software. Are you a CAD software developer? Because I (as apparently are many others)am interested to know how to scale a lofted hull or structure, (such as the max beam of a hull) while keeping all the other parameters constant - or at least not affected too adversely.
I am an engineer (and have been for over 20 years) and have so far mastered CADAM, CATIA, SDRC, PRO-E, Inventor, Mechanical Desktop and a few others that I might have forgotten, and have not found an easy way to do this (yet). I suppose you could place a variable parameter value on the "bulkhead" beam(or whatever you are using for the lofted solid) so that you could vary it external to the software. It would have to vary over some function of waterline length so that you still maintained a smooth transition from bow to stern. Then it would have to do that while still achieving the target prismatic coefficient, rocker, etc. I guess it's do-able but I've never tried it (only becaue it's easier to have a table driven set of parameters and have this generated from a spreadhseet, or even the ASCII output of a code. (But I guess you would prefer to call that an abacus...)

If you want, you can reply offline so this doesn't seem as hostile as it does reading it on the forum - which happens too often! Or better yet, E-mail me and we can talk by phone.

Steve Bellavia

my background isn't nearly as diverse as yours.

I'm not even an engineer, which makes this point all the more hilarious. I used to design paintball gun bodies. We did all kinds of custom designs involving very tight tolerances for air-tight chambers, valves and electronically controlled pressure regulators. I did this as a hobby back in highschool and early days of college. I can't tell you the number of times I scaled a whole part down to size considering that several of the components were the same shape, just different dimensions depending on the model gun they were going in. I also, within solidworks (which is what I preferred to use, rather than R14 or ProE) could setup dependent dimension variables that would, on-the-fly, re-calculate itself once I specified the relationship. And this is all on software that is at least 3 or 4 years old, and elementary by CAD standards. When it came time to send our drawings off to the shop, there were no complaints, no design flaws that couldn't be solved simply by loading up the drawing and changing something within 5 minutes. In fact, the biggest design flaw I can remember was after all the parts had been fabbed, the shop tried to put the valve assembly together, and I had accidentally put the valve striker pin in the valve body in reverse on the drawing, which physically can't happen. We thought we had 1000 defective units until I studyied the drawing for 20 minutes, slapped myself on the forehead and never forgave myself afterwards.

Thats about the extent of my "engineering." I've never really cared for engineers, considering I always had to fix their flub-ups on campus (I was the IT manager for the Industrial Engineering Dept) and received little to no personal gratitude from the constituency.

Chip on the shoulder? Probably.

Solid Works - never used it, but our design department came very close to buying it for their 20 or so designers. It looked nice.

OK, so how about this(at least at and below the waterline):

1. Assume ALL cross sections are a known 2-D shape that you can caluclate the area (and thus the integrated volume over length) - such as an ellipse (or actually semi-ellipse - I am very pro-ellipse - it's a great shape!).
2. Assume that the center of the ellipse is always at the waterline, Thus the (semi) ellipses start off vertical and become hroizontal, and at midships, they transition to a perfect (semi) circle.
3. Now there are only 2 "scalable" dimensions for each section as you transverse from bow to stern, the major and minor axis of each ellipse (sounds easy).
4. If you keep the displacment constant (say 100KG per hull - it's weight and one sailor), and a known prismatic (say .67), then you have defined the central "ellipse".
5. Now the hard part - vary the height/width of all the ellipses in a uniform manner, maintaining the displacment and prismatic - rocker will be a fall-out. Enter it into a spreadsheet for various hull lengths and you can have Pro-E or others gnerate and loft these sections for each hull length. Then you can calculate the actual hull weight (based on a skin thickness, wetted surface etc). then you can vary prismatic again, or displacemnt or whatever and you now have your "rubber" CAD produced hull. Try heeling it a little to see what happens to wetted surface, etc...

What good this does, I don't know, but it was a fun mental exercise. Then above the waterline is realy tricky with reserve buoyancy, windage, "wave piercing" ability, and other considerations.

Anyone want to do this? Maybe I'll give it a try.

Steven,

Lots of fancy words in there, I'm not but a humble pirate

but that sounds like it could work, and ProE could definitely do it, from what I know of the software.

Solidworks is good from a small parts to assembly type project where you need to do a lot of prototyping with a 3d printer before you take stuff to the shop.

I particularly liked the setup we had in the lab at school where I just exported the shape to the 3d prototyper and 4 hours later I had an exact resin replica of the part that was on my screen.

Not sure that it would be suited to hull design though.

Carl,

No it wasn't much of a problem, having four hulls just means you have to make them relatively short and fat, just like Bill was implying.

As for it taking the weight of someone standing on one end, four hulls are an advantage as all the bouyancy is in the corners. In fact comparing it with the A class 18ft cat it can carry about 10% more longitudanal/pitching moment, even though its only a 16 ft boat.

Also four short fat hulls give less wetted surface area than two long thin ones.

All the best

Gareth
www.fourhulls.com

Really a great design Gareth, fun just to look at .

What is the next project. ?

I,m stuck on the idea of a planning type catamaran , I watch the Aussie 18 skiffs and can,t help but think a planning catamaran platform would be potentially much faster and handle tacks gibes and waves much better -
The skiffs tend to nose dive going slow ,--but do they fly with their lifting extended spinakkers and their 10 ft crew wing racks.
http://www.ics.uci.edu/~truesdel/images/ellabache.a.gif

A comperable cat design would have equivilant or more effective beam and enough planning hull area forward.

I don,t think the 60 ft Palier cat hull design is the answer ,--via seaplane shape,and 50 some ft beam with 2 masts .
though a great looking design and getting closer,
it should be very fast in high winds.
http://www.parlier.org/site02/accueil/navigation/navigation1.jpg

I think either a more extreme canted hull and developing a flat or inverted bottom hull shape{ vertically actually a V shape at rest },designed for hull up sailing mode and heel, that worked with an integral fin or hull bottom extension inward at station 2 or 3 back would project much more area forward to provide lift , and help balance a more forward spin on an extended spinpole-

or design option 2 more like the 60 tris ,-use the hull area less and rely more on forward canted board area to provide lift . that would require an aft board as well for balance ,--2 in each hull one for --one aft , and a way to raise and lower them at speed .
Some of the speed sailing craft are experimenting with this on cat platform though in more pure foiler form --
Spitfire http://marine.bdg.com.au/spitfire12.html
The problem with foilers is the need for flat water and falling off plane and crashing .
Seems a partial planning hull would be more ideal for all around use and in seas or gusting conditions.

Liked the molded in swept back forward fin or skeg design idea as it is lighter simpler ,has no moving parts , stronger and less prone to damage , except beaching .
They would need to be angled back and strong .

Designing in the location aft from the bow as an inward extension foil of the flatter bottom hull requires an ideal angle relative to hull as it radiused upward in side rocker profile . This is the area that needs experimentation and and some trial testing with variation.

Some combination of the two may be the ideal .

No doubt a planning hull would be slower in light wind until it reached planning speed ,but offsetting this comparatively would be a larger beam larger bow larger sail area design . but what fun at high speeds.

Currently sail an Inter 20 , it has wide flat hull sections forward and 6 degree canted hulls a 215 sq ft main -53 jib and 270 spin at a 390 weight. With spin on a 12 ft snuffer it does lift somewhat , the hulls in flat water evan without spin on a high speed reach will at times get up and the boat feels like it is beginning to skip or skim , but just not enough yet.
Seems a lighter wider hull -more powerfull sail plan larger total beam cat would plane .
The problem then most encounter is a pounding or slamming hull , but if the sail plan is lifting it should reduce that effect ,--as opposed to a powerboat with its heavy engine weight and no continuous lift .
Watch video of sail boards at speed in seas ,-they fly and float down on the wind . Boardsail a bit, have an old Mystral board.
Then control at speeds becomes the concern and locking yourself into a trapped out position in which distance racing in seas is the norm on high speed cats clipping into a stern safety line and sometimes a forward lead line so your not blasted off the back by a wave ..

The Marstom 20 reports a 30 knot GPS speed , lifting on the hull in a semi plane .
http://www.sailcenter.se/administration/Boats/M20/index.asp

The true planning type cat can't be too far off.
There is most likely an ideal length platform that is optimum for a planning cat hull ,-

If any build one soon ,--please call me if crew is needed .

Suggested on the distance race section on Catsailor on the Atlantic 1000 thread that just as the older Worrell 1000 had in the 80s they consider again adding an open design class to race the Atlantic 1000 . The rule was a 20 ft length but no other limits on design , Boats had to get out through surf , sail through shoals .mud flats around jetties and Capes like Diamond shoals at Cape Hatteras and in sometimes large Atlantic seas.

I,d like to see this again and a class of open design development cats , the F-14 is a good start, but I,m not sailing 1000 miles of Atlantic Ocean on one

The 20s or evan 22s max L which would make Bill and a few A 22 CATSAILORS happy I know .
Think this would be a great addition to what has always been the most extreme beachcat race and draw in much more international interest as a showcase for builders and innovative design.

all the best
Carl
.

I have designed and built an A-cat that comes close to planing, or sure looked like it was when I had it out going downwind in 25 knots of wind. It is a hard chined shape that is v'd at the front then flattens out toward the rear and has a step at the 16 foot mark from the front. I will attach a copy of the 16 footer that I have been toying with making to give you an idea of what it looks like. Sadly, my construction skills were lacking, and I overbuilt some areas of the hulls, so they wound up being pretty heavy at 55 lbs each, so it will probably never perform up to class standards. Plus in sawing off the bottom of the first attempt at a design, there were several things that I had to do that have pretty much made this a peice of crap. It still sails though even if it looks bad!

Bill Roberts has said that there is not much difference in speed between a planing cat and a regular dispacement hull of similar size and fineness ratios. I think that he is likely right from what I have seen with this boat. There are several issues that i have to deal with to see if I can get it going faster, including getting a stiffer mast, but what I have experienced so far, I do not think that it will outperform any decent a-cat out there now. Given enough wind, it can sure blast away downwind, but I have no other decent boat around here to compare it to. That just means that i have to travel to find out. If I can get it going decent this summer, I am going to try making those shorter hulls at 35 lbs each versus the 50 lb ones I now have.

Hi Conrad

Looks interesting ,- I built a similar flat bottom hard chine 20 footer , though some time ago .
Used the stringer frame method per Gougeon Brothers -West System expoxy with spruce stringers marine plywd. and 3 mm skins ,--fairly simple if you set up a strong back to hold the bulkhead frames in place , as the force of bending scarfed plywood panels will try to pull it out of shape ,--as you know , or ideally have help and attach both sides together .
For a home builder this shape is very easy , another good reason to develop this shape planning type hull further.

I could not make out the lines exactly ,it looks like there is a little flair out along the aft waterline via older powerboat designs . looks good . Could not see the step at 16 ft aft .. The bow looks unusual with the knuckle and straight line the first 2 ft or so .

The 20 design had much more rocker and curved upward from mid point forward progressively more . It weighed under 40 each hull . not too bad .
One interesting feature I tryed was molding in two shorter skegs on each hull along each chine , the idea was not wanting to disturb the flat planning area along the hull center . The original looked like a double dart type skeg .
It would take the beach better that way also.

I experimented with an angular rig at the time also on it . lots of fun .

You might look at the Formula 16 class ,-if its a 16 ,
It has a 230 min weight , 28 ft mast L -
varied sail area for one or 2 .
Some excellent boats to race with.
http://www.geocities.com/F16HPclass/

What type of mast section are you looking for , some may help there , check out the Formula forums also .

thanks for the plan view -
all the best
Carl

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 😛

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.

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 😛

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