3D CAD models of beachcat hulls

Hi Grob

Wow ,really nice looking hull . thanks for posting the pic , I,m a fan of MM cat designs , their most recent A Class cat looks great .

I have something called Data cad 10 but hardly use it ,-I,m one of those dinosaurs that still use a pencil , so I,m not much help but like the idea.

Some classes like the Tornado for example are common knowledge and made available for home construction .Lines sections and volume calc -PC # wetted surface ,--CLR CE sail plan etc would be fun for those types ,--but we will have to be carefull about newer designs by individual firms and I suspect get their permission .
The intelectual property aspect I think would protect the authors rights on other designs so we should be carefull,--not a lawyer but this most likely would fall into this category even though all basic boats are published with {class} specifications ,though these just basics as per rated Length -board area- board depth- rated weight and rated sail area per ISAF requirements. The hull sections lines and actual design may be something the designer wants to sell themselves or not made available to a competitive design firm .

I,m sure the interpretation and laws may be different in various countries on intelectual property ,-It protects your fold up 4 huller as well, though you may have an actual patent and international patent on it ,

The intent is an excellent one -scientific research ,and this would really help many sailors to understand the basics of design and serve potential Formula Classes and help refine catamaran rating ,
-but again some newer designs may be off limits and may conflict with a design firms wishes .

Maybe someone more knowledgable on this would comment on designs off limits and those that are O K to examine in detail with hull sections and specifics of basic design .

We could start with the Tornado which is used as a benchmark of sorts for cat design , suggest just posting the pic , L and basic section dimentions then let others calc the various comparisons at various angles of heel and submersion from sail forces and crew weight .

There is some nice looking boat specific cad software available
http://home.att.net/~hcyoung/
http://www.vacantisw.com/
http://www.westlawn.org/student_center/yacht_design_software.shtml

A group just started a Formula 14 class concept with fairly open rules , just L 14,3 and a 24 ft mast with 300 sq ft max sail area in any configuration .

Unlimited beam ,-any sail plan configuration within 24 ft
any hull shape or number of -hulls .

Some have built ht type 14s that weight 107Lbs ,-
there are production types like Mystere 4,3
H-14 Trac 14 N 450 Wave -the production boats weight 240 and up ---Some design comparison and performance annalysis might be fun there ,--It would help future F-14 rules and the potential of sub categories as numbers grow in class --They may have 3 eventually that they find needed
due to potential speed differences .--antisipate a HT Category for lightweight designs that will include the more experimental type creations allowed within open rules ,like 14 ft beam craft with 2 masts ,-or a tri configuration or tunnen hull scow type .--a Production category for 230 and up weight boats that will be the majority at first in another category .

Beyond C Class cats with solid wing sails the only other development classes are the A Class with 7.5 beam limits and no angled boards ,150 sq ft sail ar ,-160 min weight ,
and the seldom built 18 sq class with unlimited beam on 18 ft L and 193 sq ft of sail . It would be good to see this type of class in this size renued maybe longer with spin added .

The C class designs at 25 ft and 14 beam with 300 max sail area due to its light weight to length ratio seem to concentrate on minimizing wetted surface area in hull design .
The new F-14s present a completely different set of problems due to human scale -weight ,-sail forces etc .

It might be interesting to take some existing hull design and just try variables out on it ,--like wider transom on an A class cat design ,then predict its speed potential comparison ,-though they wildthing downwind .

The variables are really interesting and think evan experienced designers often fool themselves with test tank type and formula data between theory and practical function.
Inspiration and insight being wonderfull unknown human quantities.

Maybe we could pick a Length class category and start there and examine one a week . It is very boring stuff for some ,--maybe Rick would add a design -build specific forum category for those interested.

I,m strictly an amature ,but always interested in learning more

a few other boat CAD packages..
First is an Aussie package .. I like it because its Aussie and more importantly its free.. in the basic version for students..
http://www.hullform.com/

Another I have seen used is Maxiform from http://www.formsys.com/

You are right about this thats why I only want to use stuff in the public domain, so don't send me plans unless they are freely available, and its probably best to tell me the source of the drawing so I can make my own judgement.

I don't think I am doing anything wrong here, this is something we do all the time in the auto industry. Indeed many companies make a living out of collating and selling this type of information.

All the best

Gareth
www.fourhulls.com

I am totally ignorant regarding design. Can either of you propose a good primer as a starting point?

Hi Pete

its dated but think it was Skene,s elements of yacht design that got me started ,-
http://www.sportsreading.com/Skenes_Elements_of_Yacht_Design_0396079687.html

It goes thru the basics ,though applied more to sailing yacht than beach cats ,--but the basic calc and formulas apply ,--just differently with two hulls and no lead mine keel below.
model building or the actual thing , then application of these and final design becomes all to real as any error becomes obvious ,-this is the hard way but best way to really learn . Hope we see a resurgence of cat designs and interest encouraged by limited development type racing classes to test then out in.
You read about a number of home builders or catsailors planning a cat project.

Thanks Grob --boat designs in public domain

it is kind of a grey area ,-wasn,t sure .

VoloView by Autodesk (AutoCAD) used to be availble for free download. It has ability to open dwg files, and should have the ability to "orbit" your 3-d model. Hence, you could distribute dwg files if you wished. I am not very familar with VoloView so I maybe wrong.

Hi Carl, thanks.

What I'm really after is a boat with the stability and seaworthiness of my Tiki 21 with the performance of a Hobie 16.

It's probably a pipe dream, but I'd like to be able to form a more educated opinion.

Any comments?

Hi,

I have all the data for my own design for an A-Class hull. Hopefully the attached image files work.
I used a spreadsheet attempting to minimize wetted surface (elliptical-circular-ellptical sections), maintain a target prismatic coefficient, while minimizing the rate of change of displacement/frontal area from fron to back. It ened up with a little bit of rocker, which I thought was nice, but can't explain why. There are much more sophisticated ways of doing this, such as using Taylor Series expansions to minimize/maximize certain variables, but I don't have time yet for this. Anyway, E-mail me and I'll send you my spreadsheets...

Steve Bellavia
Hobie FX-1 Sail #211

Hi Grob,

IGES seems to be the most universal format for surface data. Multisurf, Rhino ICEM and many CAD systems support IGES.(you are using Pro-E?)

Modeling is a nice way to get hydrostatics on a hull.

Without CAD maybe... for catamarans maybe bonjean curves or longitudinal metacenter vs displacement would be useful.

Cool project as long as nobody gets mad.

Talk to you later
-colin

Pete, I would reccomend

Principles of Yacht Design by Lars Larsson, Rolf E. Eliasson
http://www.amazon.com/exec/obidos/t... 103-7971006-7374220?v=glance&s=books

All the best

Gareth

Colin, yep I use Pro-E, that background is a giveaway

Hi Pete

My guess is Grob,s recomendation on the basics of design is better,--Skene,s is very dated ,-got it more than a few decades ago

On over 21 ft cruising cats ,- H-makes a 21 sport ,buts its heavy ,--The Stiletto 23 was a nice platform with not quite enough hull volume for a berth though .
The real problem getting performance in a larger cruising cat is having enough sail area ,-but then a capsize and righting become a concern .

A modified Supercat20 or Arc22 with a smaller cruiser type or reefable sail plan may be worth while ,-Bill designed the neat stay extender lever hardware to solve the righting problem ,--have a SC 15 for the kids ,--it works great .

You might find a used one very reasonably that needs sails or minor repair , Maybe a slighter shorter mast and sail plan on it would make an excellent fast coastal day cruiser that numerous people could sail without being overloaded .

There are some newer mid sized cats on the market ,but extremely expencive .

hope that helps .

Thanks to all. I'll order the book, see if it makes any sense to me (had a tough time with college algegra!).

In the mean time, I'll start pricing those two boats.

Thanks again.

Is there any way to post any dwg. or dxf. or iges. file on the forum. I use Rhino and Multi-surf. I have some hull models ive built for the F-16 class, The open rules for f-14 looks like fun!
Ricky

render it as a jpg from within autocad.

attach that.

Hi Gareth,
Let me explain briefly about hull/boat design. Boats are designed with numbers, many many many numbers and ratios of many numbers and numbers raised to powers, etc. Long before the first hull line is put on paper, that hull shape is described in terms of numbers which are necessary to meet various requirements for the hull design. The same is true for the mast and sail plan and the centerboard and rudder. It is all numbers. The last step is to draw the picture, the geometry, that satisfies the numbers, the ratios, etc.
To draw use CAD and draw pretty pictures of hull shapes without knowing and understanding the numbers, the rules and the goals, of the hull design leaves many many unknowns which could be called guesses. The beauty of running the numbers first is that if some performance or behavioral characteristic of the design is undesireable, change the numbers, iterate, until a satisfactory solution is found. It is much quicker and less expensive to do it this way.
Bill

Hi Bill

Great racing recently , running aground ,snapping a rudder, capsizing ,-righting and sailing well to win O A always makes the finish a little more rewarding.
race story -
http://www.catsailor.com/Stories_Temp/Stplchs03.htm

Agree --a general design discussion of hulls only of various sizes and different intended functions will not be benificial unless targeted to a specific type and with a broader understanding of design .

The knowledge and experience gained from designing and producing a series of successfull cat designs ranging from 15 to 30 ft --SC 15 --17 19-- 20 --Arc 21 22 RC 25 -27 and a 30 --and I,m sure a wide range of experimental type craft in between , now allows the ready applicable calc. or formula for a particular cat. size and desired function within a targeted design criteria. From going through this catamaran design exercize successfully numerous times you have the wonderfull ability to apply the correct series of engineering calc required , and can readily recall them having real models of each to relate to .
SC link http://www.aquarius-sail.com/

I like Gareth's idea , I,m here to learn more , think your correctly stating that if the design comparisons are to be benificial they should target a specific type ,but also that Naval architecture is complex and it will take some time to comprehend the intrical aspects .
--It would still be interesting to discuss design, several do have auto cad to help visualize it all .
There are numerous sites with basic lines and jpg pics for comparison also , this from the Aussie C cat challenge group . http://www.lacaustralia.com/design/challenge.htm

It may start with the A Class per example used per pic .
Some great video from the Worlds here
http://a-class.org.nz/photos_2004_worlds_video.htm
Defining all basic elements of catamaran design then applying them to targeted design criteria and type like A Class cats ,-then other design development class categories .

Like the A Class intnl reference to {big pond }
as opposed to a big fish in a small pond
http://www.users.bigpond.com/aiadca/index.html

a Class rules and basic boat specs are here -
http://www.usaca.info/

One interesting aspect of this class is many designers also race in it . So sailing techniques and practical insights instincts and intuition also come into play .
The downwind sailing technique of hull up with crew back may lead some larger crew to desire more volume towards the stern for example.
The A-s are highly refined and specialized type with matching mast flex and sail to crew weight as well.

It would be very interesting to run through variables of design in A-s - typical design --then add volume in the sterns and run through the numbers and a visual pic to relate it to ,--then canted hulls - etc .

It might be best if Rick set up a Design build specific category on Catsailor .

All the best Bill -& Gareth

Carl R

Hi Carl,
My point is that if you don't know what you are doing, you don't know what you've got.
Adrenalin is an example of a boat that was built to an exciting idea, pivoting amas, with incomplete analysis and understanding. Pivoting amas should move through the water with less drag than fixed amas. Less drag means more speed. What a great idea. Evidently no forward stability calculations were done. This proved to be the boat's downfall. The boat originally had a 76ft tall mast on it. A few downwind runs/reaches and the mast was shortened to 56ft. Why??? When the amas pivot as forward pitching moment increases, they provide no increase in pitchpole resistance. The boat wanted to dive all the time. This design was very deficient in pitchpole resistance due to the "pivoting" amas. A few minutes of forward stability calculations would have said, "hey, wait a minute; we have a problem".
Sailing World magazine said this boat was a "world beater, a breakthrough design for trimarans". The last thing I heard about the boat was that it sits abandoned in an old boatyard with weeds growing up around it several feet tall.
A few minutes of calculations and analysis could have made a big difference here in time and effort and dollars spent.
Bill

The "Wooden Boat" article on Adrenalin got my adrenalin going. Sorry to hear about the ultimate outcome.

On another topic, I'd like to increase the light air performance of my Tiki 21. In my thinking, the most economic way would be to buy an existing rig from an old beach cat and just stick it on. But, which one? There are so many, surely one would work.

Any thoughts?

Bill,

Which of these "numbers" do you think are most relevant to beach cat design, my understanding is that these hull design numbers are just simplistic ways of describing the hull form and 3D CAD does a much more accurate job.

Certainly to take your example of stability, we can get much more accurate estimates from the 3D CAD data of the hulls.

I am not saying that anyone would start a hull design by making a pretty 3D model, but for reverse engineering existing designs it is probably the best way.

I am genuinely very interested in the design process you use to define a hull shape.

All the best

Gareth

Hi Bill

The 60 ft Parlier planning cat is on the water--congrates to the sailing team . Looks good .
http://www.parlier.org/site02/accueil/navigation/navigation3.jpg

It is nice to see innovation ,-though it will take some added refinment and sea trials to perfect this type of design.

agree completely with your comments -
A plan review and basic calcs with recommendations on any plan is generally a small portion of total budget ,-and the best time and or money spent .

Adrenaline -the Prosail raced FORMULA 40 -ft tri .
I watched it sail several times in the Prosail events from a H-21 participant veiwpoint in the other class.
It is quite a site to be racing on a crowded harbor like Newport in high winds and powerboat chop in all directions straining up on the port layline headed for the A mark and seeing a 40 long 40 ft wide tri round and start its downwind leg aiming straight at you doing about 25 . whew!
No where to go ,-difficult to get around a 40 ft wide craft doing 25 .

In fairness to Adrenalin ,The Prosail event organizers purposely picked the breeziest venues and times of year at each to insure good high windspeeds.

Its amas were small and pivoted for and aft ,
there was some research done on the pivoting concept by the Parliere design team earlier --shown in a video
http://www.parlier.org/site02/accueil/1024x768.html

The idea in Adrenalin was the amas would stabalize the platform, and to reduce sail area as needed though it was optimized for light wind conditions,-

Latter tri designs do have full 100 % volume amas ,{though fixed} good roller furler and reef systems ,and are very fast 30 ft tris that still race on Saginaw Bay MI http://www.sbyra.com/
and in the MAC races in the multihull div.
http://www.chicagomackinac.com/2003/

Comparative study of similar class category boats I think is Grobs perspective and goal from having available cad system drawings available , that rather than creating something from scratch .
-
I,m interested in the Formula 14s though-
It has only L -14,3 --a 24 ft mast max.-- and 300 total sq ft of sail as current rules , though should add a production class sub category with min boat weight etc .

It might be fun to walk through a Formula 14 design , though no two will agree on all design aspects.
Maybe we will see a 14 ft replica type 14 ft beam --2 masted Formula 14 soon ,-per 60 ft cat design .
Though as you noted if the proper hull volume ,calc waterlines ,displacement, moments ,boat and crew weight ,-bow sections hull shape ,structural engineering ,loads or crossbeams and stays -fittings and harware , sail area forces -heeling effects ,-hull design ,boards and rudders ,and numerous other design aspects given consideration it chalked up as a learning experience.

Interesting perspective drawings and seaworthiness articles for design consideration on this site ,-for larger multihull designs.
http://www.steamradio.com/JSYD/Articles/NESTalk.html

Hi Gareth,
Hull length is by far the most important hull dimension. I also point out that hulls, especially short ones don't scale. This F14 boat that we are talking about must support the same weight as an A cat for example. If you scaled an A cat hull down to 14ft, the length would scale down by 14/18 and the width would scale down by 14/18 and the depth would scale down by 14/18. All of the sudden we are looking at a scaled down hull that has 47% as much displacement as the A cat hull and it must support the same weight. That won't work.
So we have to do something like this: If the length of the boat is 14/18 as long as the A cat and it must support the same weight, then the hull width distribution must be 18/14 as wide as an A cat with a similiar keel rocker. Now we have a hull shape that will at least float on a reasonable water line. Now you see that we have gone way down in hull fineness ratio, shorter and fatter. But this is necessary in a short boat.
Bill

bill,

statements like these make me wonder if you've ever used CAD software before.

Crunching numbers? with CAD you can crunch the numbers and have the results graphically interpretted instantly.

Change the dimension of the beam, and if its scaled properly in the drawing, it will scale the rest of associated dimension to match.

I mean, aircraft and automobile designers rely on CAD to do their calculations for them, I can't imagine a boat designer couldn't.

Maugan17,
I am showing the numbers, example, so you will understand how to go from one size boat to another and know what you've got when you get there. The method, the logic, the how to do it, is much more important than an answer. If you don't understand "how you got there" when you arrive at an answer, you have no idea as to the validity of the answer.
An A cat scaled down to 14ft would really look slick. A Tornado scaled down to 14ft would look like a hot ticket. The only problem with these scaled down boats is that when you got on one, your weight would sink it.
Boat/hull design is not playing games with CAD on a computer.
Bill

Hi Grob

Wasn,t the volume calc and getting enough displacement in your 4 hull design the biggest problem ? -estimating a 4 ft hull dbl ended does not provide much ,-each hull need to support a crew if they stepped aboard at one end .

Looking at some of the C Class designs -they are L- 25 ft
BEAM 14 FT - SAIL AR 300 no min wgt.

here is a beauti from the Aussie C Class cat challenge
http://www.lacaustralia.com/images/hull_global_1.jpg

funny ,-the F-14s have a 300 sail area

Anyway , at this L , volume in hulls or sail carrying ability -stability is less a problem

Designers of these with their extremely fime L to hull beam ratio seem to concentrate on reducing wetted surface area to its theoretic min..
Hulls with the least w a are U shaped , which contains the largest volume with least surface area with proper volume calc per each section to support hull crew total boat weight and factoring in sail forces and heel with sailing modes from light wind to one hull up.

Hulls are generally divided up into 10 sections along its length ,-these are sometimes overlayed and deck lines added
here is an older {hand drawn } 18 sq meter provided by Dick Lemke -
http://www.catsailor.com/bb_files/28263-smnacra2.jpg

You can enlarge it --you will see sections --bow on right half -stern sections l half --side profiles and wl
and half deck plan - basic lines drawing-

Quite a difference between the 18 sq and the C Class -

The C s in section drawing would show U sections with much more rocker in side profile.
Check out the MM C Class freedom,s wing ,--it has a great amount of Rocker { for and aft curve to the hull profile } having high upturned bows and sterns as opposed to the more straight lined side profile of other types .
http://www.morrellimelvin.com/page31.html

If the designers goal is to reduce wetted surface area and thus frictional resistance to a min , then each of the 10 sections would be proportionally sized from the narrow bow in U SHAPE and progressive proportional depth ,--shallow entry bow to deeper U center to narrower shallower stern ,
thus the basic C Class hull shape -
check the UK C Class entry ,-it looks similar -
http://www.team-invictus.co.uk/invictus.htm

Some designers use a PC comparison number -which stands for prismatic coefficient ,-which is the area of underwater hull of greatest section expressed as a solid per L compared to actual hull . I,m not sure about this for multihulls or how effective this is .

A pc IN THE LOW .50s is very fine ended with little wetted surface , but will cause limits in form and wave making resistance earlier than the fuller bow and stern type hull designs with straighter profile and less rocker.

A direct comparison with another C Class cat -via cad as you suggest would be a much more effective prediction of speed potential .

I,m hoping to see some via cad .

Hope that may be a helpfull starting point to reference hull types , these C s are the deeper displ types ,-
They are faster in light wind as the main form of drag percentage wise is frictional resistance at lower speeds .

As speeds increase form drag becomes more predominant in limiting speed of displacement hulls .

The interesting trend in hull design per example of MM A Class cat or designs like the Marstrom 20 is flatter forward hull sections hoping to use hydrodynamic lift to reduce form drag by lifting it partially at speed along with canting the hulls .
speculation as to effectiveness,--

Think the C Class type hull of same L and sail ar wins in light winds and choppy seas ,-but the flatter type wins in higher winds and flatter water ,-varied with each .
If the C Class cats with higher total displ hull speed with longer L know the venue they will be racing in and time of year with average predicted wind speed ,they can optimize the design for those conditions -

Its quite a game at that level

Bill's right on this one ..If you surface on ICEM or Alias or catia v4 they are b-spline or bezier,or nurb surface...not parametric so they wont update with dimension changes..if you do them in a parametric system than yes they can and will update if set up properly..keep in mind that inside fillet operations can and do fail upon dimensional updates causing the need for freeform surfacing.
we have lots of designers straight out of college who have no idea what true length of line means.You need to know the formulas then the cad will help you tweak them quicker.BTW Iges is not reliable for acurate surface data transfer in my opinion.

In reply to Bill Roberts

I found a lot of things didn't scale to 14 ft. In fact I have deep respect for a designer who can create a 13-15 ft cat, that can hold normal sized people, go fast and not do something strange when it hits the edge of it's envelope.

In response to Maugan.

Yes auto designers use CAD. However, it is not like magic. The CAD program does not do all the work. The CAD model acts like a common interface to let the engineering teams perform their work and then return their inputs. That does not sound like much until you realize that normally, a project engineer sends a design to the engineering teams. The engineering teams laboriously create models using their tools and return their results. Finally the project engineer iterates with the teams to produce an acceptable design. This is great until one night the project engineer wakes up in a cold sweat thinking, how can I be sure all the teams are modeling the same thing? Did acoustics include my 5th wheel or they they think it was a coffee stain on the drawing?

There are some Analysis/CAD systems that will let you design and analyze simple systems, like catamarans, but they are very high dollar and still require experience to interpret the results. Also they need to be calibrated against reality for every type of system you will use it for, at least once.

In Reply to MauganH17,

Wow, taking a shot at Bill Roberts. Not something I would be comfortable doing.

You can't crunch the type of numbers Bill is talking about with CAD. In aerospace (my field), the CAD stuff is at the end of the analysis-design cycle, and I suspect in high performance hull design it is the same. The CAD may tell you what you've got, but it certainly doesn't get you there. During the iteration process you can import the CAD model into a CFD code to "test" what you've ended up with - a digital wind tunnel (or tow tank in this case). I always got a kick out of the assembly technicians in the Grumman F-14 facility who would say "what do we need these dumb aerospace engineers for? We can build this plane just fine without them". My reply was "But where would you get the parts from?"

I think I would listen to whatever Bill has to say - he's been analyzing, designing and building very successful platforms for many years.

Steve