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

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 -http://www.catsailor.com/bb_files/30231-Monster.JPG
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