Where are the catamaran innovations?

Tortured plywood

I've built several hulls very quickly with great results using thin plywood and no framing. You cut the sides of the hulls sandwiched together so they are perfectly symmetrical -- adding rocker as you see fit, deck.... You can join them along the bottom to form a V keel or lay them on a sheet of plywood that forms a bottom. Tack them in place with CA. Add a little carbon if the joints are under strain. If you added a bottom sheet you trim it AFTER the boat is all epoxied together with reinforced carbon joints. You then use Styrofoam sheets to "torture" hulls into more complex shapes. So you effectively built the frame second, which is very quick to do. I use urethane foam to glue these pieces in place. Lastly you flip the hulls over onto sheets of plywood (pre-sealed) and glue them on to make the decks. Use vertical foam sheet to support the decks if you plan to stand on them.

This produces hulls in a few hours that weigh very little. A 1X1 ft box cross-section weighs just over a pound per foot of boat. Critical attachment areas add more to the overall weight, but the results are light and they are very quick to make.

Another variation for round bottoms is to cut sharp V's into plywood sheets and bend the V's up to form a bow and the uncut portion forms a nice round bottom with maybe a minimum 6in radius. The only limitation is that you can't have any rocker in the round bottom areas, so I use this technique to extend existing transoms where you basically want no more rocker, but a round bottom. For example I added 11ft to my trimaran's transom that was incredibly light and strong. (Try 2 sheets of carbon layup versus a carbon-plywood-carbon sandwich layup. The first sheet is a noodle, and the second you can stand on.)

Related to this, a huge advantage of using plywood and carbon is that it is much more puncture proof than carbon-foam-carbon and it cannot absorb water.

Has anybody else tried frameless or minimal framing techniques?

 

Any pictures of your method?

 

I don't have pictures of the process, but here is a boat that was built in about 25 hours using this technique cobbled with lots of parts. The main hull took about 10 hours. It is an extensively modified small, cat hull that is now 22ft. The amas took about 3 hours. Most of the hull times are consumed in painting and finishing. Putting everything together took maybe the rest of the hours.

http://s371.photobucket.com/albums/oo159/johnelliott24/Precarious the trimaran/

I just built some small amas a few days ago for a new boat and attached foils. The amas took a few hours. Attaching the foils took longer. I'll take some photos soon.

 

"My impression-- and I could be completely wrong-- is that tortured ply is a chancy thing for a designer to work with, and that there's a risk the hulls will not shape up as the designer intends. Prototypes would always be necessary, and it seems as if a lot of designers don't want to build a prototype as part of the design process."

A lot of the info can come from the model, which is easily made out of aircraft ply. Depends how long it takes to get the layout info on the aircraft ply but after that it is easily constructed using 5 minute epoxy. The ply can be cut with scissors, so it is pretty easy to try a few developments.

It is an ideal method if one wants to make amas or similar small hulls. It is also a lot of fun. Personally I think it tops out around 35 feet on a cat hull, and that would be best in CM.

There are some cost savings, as normally one can make better use of materials than with a multichine design, and there is far less glass and epoxy used.

I think some of the problems go away on the home front. If you want a small hull, you can just make it and figure out what to do with it later. That is basically what I did when making my small cat. I just designed the hulls and assembled them as I went along, no grand plan, except a single sheet with profile and plan view for the hulls decks and beams, and a weight budget. The process would be the same with tortured hulls just the result would have been sliprier. If one didn't want to caculate the hydro, one could just go down to the water and sit on a hull and see where the CB was, or even do that with the model.

"The only limitation is that you can't have any rocker in the round bottom areas"

Another limitation is that the transition isn't smooth. If one is willing to do the keel joint, the shape is much better, however it almost always doubles the ply use on all but the smallest hulls. Not an issue on serious boats though. Like I have these amas that have been in my driveway for the last 20 years, and the fact I tortured then with a keel joint cost me 15 bucks an ama extra, plus epoxy in the keel joint, and a few hours work. Worth it over the years for the view alone. On a fun knock it out project though, it might not pay off.

 

"To put it another way, where is the Jim Michalak of multihull design? He draws simple safe designs... About the only serious designer who seems to be working in that genre is Gary Dierking."

I disagree on 3 counts:

- Those Bolger etc... simple knock together designs aren't that good. There are some wonderful ones like Elegant Punt and the Light Dory, that are based on traditional designs with ply variations and innovations. There are some workable designs with ballast, which are not all that simple or cheap. There are a bunch of promise the world designs that were horrible, dangerous or, not that big a deal. But what has grown up is a very interesting community of people who build boats pretty fast and talk up a storm.

- There are a lot of those kinds of designers out there in the multi world already, but people aren't so interested. Wharram (people are very interested) is simpler in some regards than a Bolger, there is far less bad stuff to do, and a far better results in a Tiki 30 than with an AS29. And the list of folks with simple highly evolved multi designs in ply is very long: Newick with Tremolino; Seaclipper 28; Wharram; KDesigns;Oram; lots of NZ tris seem to be coming out; Piver; Jarcat; Jones Boats in particular. And then there are guys like you and me who are throwing together simple ply boats. I would put some of Gary's boats in that class. I suppose on could add that Bolger himself has designed some multihulls, though the results are not that wonderful, to be kind. I do think his 120 degree hull is interesting, though he doesn't seem to understand what to do with it.

- Also, if one accepts that the multihull thing just won't go as down and dirty as something like a Bolger box, for the most part, there are creative people out there trying to make actual good boats that people have heard doing amazing things, very simply. Leaving aside the period when stuff like boxy ply tris was state of the art, we have: The Gougeons on folded ply; Newick with the master mold system; Constant Camber by Brown, Newick, and the Gougeons; Kurt Hughes pushing CM (whoever invented it); Kelsall with KISS. As I have mentioned with CM I think one could still make a 24 foot tri for 4-6K Canadian fairly quickly, I think that compares well to something like a water ballasted sharpie with misconceived hydro that has no reasonable means of keeping the mold at bay.

I'm a big fan of Bolger, and some Michalak stuff, I own books, and plans gallore. I have built a few of the smaller boats. I think the reality is that the multihull simplicity guys are way ahead, but they aren't simple enough for the Bolger guys, or fancy enough for where the folks drawn to the multihulls for racing or charter/liveaboard are at. Not to mention the interest in multihulls to start with is pretty small. But the real results with simple boats like the Val in the Ostar (glass but could have been ply and I think there was a later ply version to prove the point), The stacks of Wharrams doing world cruises. Heck Jones alone crossed the ocean many times in some very simple boats.

 

Gary Baigent who posts here from time to time has built a number of boats with the techniques you describe. The latest is an evil looking, dreadnought bowed, 19', wing-masted, schooner rigged mono Hopefully he'll respond.

 

Ive come into this a bit late, but ther are some new inovations for catamarans.
Design is a constant working progress with designers, in hull design and engineering to suit todays consumer that requires lighter more efficient hull forms and deck/cabin design searching for more interior room, and modern layout etc.

Steering for example.
Always a problem to get any kind of feed back, rudders so far aft that no link bar possible, and maintainence issues that drive you nuts.

There is a system that is as brilliant as it is simple.
Using flush mount steering head/s that will accomodate an autopilot/s (rotary drive) .
Center mounted cable modular control and Push/pull cables to each rudder.
(no link bar!!) full feed back and anything from 3/4 to 1 1/2 turns lock to lock (more if required) its all in the gearing at the steering head.
The P/P cables are adjustable and if required akerman can be aplied to the rudders.
The P/P cables can be routed through the cabinatry and only require an 28mm hole to pass through bulkheads.
Single or twin steering station,

I fitted this system to a 1320 meter performance cruising cat over two years ago. That year 3 months after launch it won the multihull Rendevou in Queensland Australia PHS div

The owner atrubits this, in part, to the way the system worked to give full feel back and the light feel and responce to boat.
The boat has since seen thosands of sea miles with no problems and no maintainence required.

This is good gear. unlike some atempts in the past to solve steering issues with similar equipment.


SPJ Yachts

 

Johnelliot
How do you work out what shapes you want so it floats where you want and carries the load you want etc?

 

I too like building hulls in this fashion but it seems that hull thickness has to be limited to 4mm perhaps 6mm if you are looking at getting any rounded shape at all. i haven't tried it but it seems to me it would be hard to form any shape out of 8mm ply or thicker.

This would therefore limit the maximum size hull which can be built, say 30ft max. I would love to hear from people who think different.

 

Excellent question:
How do you work out what shapes you want so it floats where you want and carries the load you want etc?

This is the hardest part. I start with simple volume calculations, but then move to testing. Sometimes I will build a 4ft or so model and other times the real thing. For example with one 22ft cat I tacked together a hull and floated it in shallow water and took pictures so I could also view and think about it later. I use myself and other people as weights to simulate rigging, crew, water weight, etc... Another example is the boat in the photos I linked to where I really missed my estimates. That boat went on one sail and was retired (but 2 new ones have replaced her).

Anyway the key is to test before finishing. You can whip something together very quickly and then spend time making it pretty later. About 50% of the time the idea is a complete throw away. But boats like the 22ft cat make up for the mistakes. She is so much better than my 20ft Tornado that you can smile through the bad prototypes. The key is to not waste time on dogs, but test them first.

 

This would therefore limit the maximum size hull which can be built, say 30ft max.

Usually the radius of the curves are greater the larger the boat, so you can use thicker plywood, but if you need some tight bends nothing stops you from layering the plywood like cold molding.

 

As far as hull thickness is concerned, stiffness goes up to the cube of thickness so there is a rapid stiffening that occurs. That does not really limit the hull size to 30 feet because the hulls can easily be structured up with re-enforcements. There is also the CM thing where ply is pre-curved to allow greater fullness and thickness. My experience with CM was inconclusive because the smaller hulls had problems I brought to attention, and I haven't built the larger ones.

My sense of the limits is really with the depth of hull that can be created with a single width of ply. Lots of boats have used wider ply, but that ends up being too awkward for my taste. I prefer to use the 4 foot section and extend the side with conventional construction. Boats as large as 35 feet have been built that way, and larger boats with odd configurations, like race boats and podcats could be built. The Gougeons worked up a Stressform plan for a 60 foot Ostar tri. Unfortunately the plan did not go ahead.

"How do you work out what shapes you want so it floats where you want and carries the load you want etc?"

With small boats you have the luxury of moving the load. With larger boats you can come at it two ways. Either design a plan using section shapes of parabolic bent ply then do the calcs the old fashioned way, or enter it in a computer. Then you have to adapt that plan to a panel projection. That is the artful part, but not so hard once you have seen a few comparatives, the expansions start to look fairly similar.

The other way, and both methods can be combined, is to build a model, or full sized hull and then take off the sections, work out the hydro, and make any adjustments from that point. Or even test the model/full size hull.

A third method is just to guess, and a lot of that has been done. This method is often combined with a relaxed attitude to outcomes. A lot of properly designed boats have been dropped in the water before the waterlines went on. A project I am working on now, though not for a tortured main hull, is being designed properly, but it is difficult to actually know what factors to plan around. I know of no similar center cockpit design of the same size. Some of the assumptions I am making may be out of the correct range and may mess things up. I may have to take a few extra turns around the design spiral to get it to work.

With the method described that doesn't use a full length keel joint, the difficulties of predicting keel curvature would be lessened, so I think the design problems would be less also.

 

I've posted this stuff before ...but here are some jpegs again. The 5.5 x 2.25 metre skimmer was built in tensioned 4mm ply over frames and a backbone. This is easier to get the shapes you want but is still tricky. You can of course get rocker into the mid sections with "true" tensioned ply by cutting curves into the base ply sections and then wiring/epoxy taping the two sides together. All this is excellently covered in the Gougeon's book. Get a copy.

 

Recent information about the Auckland/Tauranga - line honours and a class record set by a John Tetzlaff 8.5 metre (28 foot) catamaran Attitude, beating in, no thrashing, all the 50 to 60 foot monohulls and multihulls. Check out the construction.
Hi Gary,
Yes Attitude did well. I understand they saw the front coming, reefed down before it hit and were able to keep going. Good seamanship I reckon. Also good because questions had been asked about its scantlings (4mm tortured ply with 300 gsm boat cloth on the outside) and whether it was suitable for offshore. Those questions have now been answered. Good the new owner is willing to take it outside the harbour too. Shame about Catabatic - I guess we'll hear the details in the days to come.
Greg.

 

Pretty nice monohull potato chip, there, Gary..... but how do I get my hands on the Morris Woodie?

I used to have a Hillman Super Minx when in high school and always lusted after the Morris wood wagon.

Have you sailed the boat yet and how did the schooner rig work for you? I put a schooner rig on an 18.5' trimaran and it's working pretty darn good for the guy who owns the boat now.