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  #1  
Old 07-19-2009, 12:12 PM
ImaginaryNumber ImaginaryNumber is offline
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Modular Cruising Catamaran

I am looking for an owner-buildable design for a 35í (+/-) deck-bridge sailing cruising catamaran. My first constraint is that while I have plenty of room to build it where I currently live, I will have difficulty transporting a 20í wide boat to a launching area short of using a helicopter. To solve this problem Iím wondering if it would be practical to build a modular catamaran? By this I mean that all the major sections of the catamaran would be built independent of each other, transported to a launch site, then lashed or bolted together in the final configuration. I want all the components to be truckable on standard roads without major hassle. A maximum width of 8-1/2 feet is ideal. 10 feet is okay. 12 feet wide is pushing it.

Another criteria is that the boat must be easy to manage by an older couple doing short-handed sailing. Iím looking for easy to build, easy and safe to sail, easy to maintain, easy to live in.

A third constraint is that I plan to sail in colder waters, which will require insulating and heating the living quarters. I donít see that the three areas of a typical catamaran (two hulls plus bridgedeck) lend themselves to efficient heating. Too much surface area to insulate, plus temperature stratification between hulls and bridgedeck. So Iím exploring the idea of putting all the living space in a full-width bridge-deck, and using the hulls only for storage.

This configuration would have both pluses and minuses.

+Pluses include having all the living quarters all on one level (an advantage as one gets older)
+Easier to insulate and heat
+If the hulls will not be lived in perhaps that will allow a more hydrodynamically-efficient hull shape.

-Minuses include less privacy compared to a traditional catamaran. (not a major problem for me)
-Higher center of gravity, so less stable.
-Greater height, therefore probably more windage.
-If the bridgedeck was 16í-20í long and 20í wide it would have to be built in two or more pieces to meet my transportation requirements. I'm not sure how to join two bridgedeck section together, or how to join the bridgedeck ensemble to the hulls.

The ideas Iíve come up with for this last concern are:
=Split the bridgedeck transversely into two pieces, each perhaps 20í wide by 9ílong.
=Make the deck portion a plywood stress-skin panel perhaps 6Ē thick, with solid wood stringers, and foam in open spaces.
=Make the cabin(s) a lightweight bubble of 2Ē+ foam with fiberglass or thin plywood skins inside and out. (hope this pushes the COG lower)
=Place a free-standing mast in each hull, carrying either a split junk rig, cambered junk rig, or swing-wing junk rig. (These are relatively new variants of the ďstandardĒ junk rig, which have the same easy handling characteristics, but with improved windward performance.) Not using a shroud-supported mast on the deck might lessen the needed strength (AND weight) of the bridgedeck, and using two masts instead of one will help to lower the center of gravity.

Iím hoping the members of this forum would be willing to advise me whether this type of design is possible and prudent? Or what modifications could improve it? Are there similar boats already designed that Iíve missed?

Thanks for your thoughts,
i
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  #2  
Old 07-19-2009, 02:01 PM
Squidly-Diddly Squidly-Diddly is offline
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Here is my idea for modular big trailable sailing cat.

"The Cat in the Box would be a 40' cat with 40' x 4' hulls connected by poles decked with either a tramp or some sort of solid removeable decking.

I'm thinking of a aft wishbone mast cutter rig with a third windsurfer type sail aft. I'd use spare sails to construct a 3 sided tent on deck.

In either boat I'd consider using the trailer frame as a aft wish bone mast. I'd even have provision for detaching the wheels and tires and mounting them on the flat on the deck as fenders so nothing would need to be left on shore.

I think it would be possible to carry the tow vehicle itself on the deck of a Cat in the Box, including ramps for on-off loading. The 'killer app' would be to tow the boat to the beach, launch the boat, expand the scissors (poles) to separtate the hulls, use the trailer as the mast, drive the tow vehicle up ramp (or pull up with winch) and sail away. Reverse at next land fall."



I'd also want it to be Containable with standard 40' x 8' box....while still on the trailer. No "standard boat yard operations" needed to launch or pack for shipping.

I'd want a generic simple way of connecting the hulls to the beams, so more hulls could be added, or even use 8' wide hulls. I figure once you are into towing one 40' trailer, another trip isn't a big deal.

I'm aiming at a 'system' that could go from a fast, bare bones cat with only accommodations in the two narrow hulls, to a "Fat Cat" with 8' wide hulls, to a 40' x 30(?)' flat platform onto which a 40' x 30' x 10' tent could be erected for massive temporary living space.

My target market would be everything from:

Weekenders wanting a big fast cat they can tow with normal big pickup and use without berthing fees,

to resort/special event operators who would like a modular shippable system with additional dedicated Head and Shower OR Kitchen and Dining hulls,

to work/business boats.

One BIG draw back would be no obvious built in pilot house or helm, as the deck would start off being flat across the beams, so this might not be good for cold weather.
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  #3  
Old 07-19-2009, 02:23 PM
Squidly-Diddly Squidly-Diddly is offline
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PS-as part of the "system" I'd have the 8' wide hull

able to be used as the center of a tri, possibly with the amas stowable inside the main hull for trailering/shipping.

Also, a single 4' wide hull could be used with same amas, and collapse down to 8' total with amas.

If the 8' wide hull could be trusted on its own, then turn the two amas into a 20' cat! I think stowing the amas inside an 8' hull is doable.

I also think their could be a market for 8' x 40' trailerable fuel efficient day cruiser for calm waters.

Mix and match.

For resort operators and floating hotels I'd want hulls to be able to be added or subtracted 'on the water', by slipping them under the deck, so refreshed bathroom and kitchen hulls could be exchanged without main boat heading for the docks.
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  #4  
Old 07-19-2009, 03:36 PM
ImaginaryNumber ImaginaryNumber is offline
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hijack

Just my luck to have my thread hijacked first thing
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  #5  
Old 07-19-2009, 08:01 PM
nero nero is offline
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Why not look at a proa? There is one living area. Very easy to sail. Low cost build. www.harryproa.com
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  #6  
Old 07-19-2009, 11:01 PM
Alan M. Alan M. is offline
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How about a "podcat" style of boat? Something like this: http://boboramdesign.wordpress.com/46-pod-cat-for-sale/
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  #7  
Old 07-20-2009, 02:32 AM
bill broome bill broome is offline
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look at woods designs, he has several with separate accommodation in a pod, and some are purpose designed for assembly at water's edge.
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  #8  
Old 07-20-2009, 06:26 AM
catsketcher catsketcher is offline
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Imagine a great idea

Every time I build a boat I have the same thought - My next boat is going to be square!

I have had this thought about a modular cat a few times. Hulls are good but hard to build accommodations into. Great for bunks (I know they are accommodations) and storage bins but a hassle to fair and finish. So I had a modular cat come into my head a while ago.

My 38footer basically has three bridgedeck sections

1- a full bridgedeck section containing the double berths
2- the bridgedeck cabin
3- the cockpit and aft deck

If I was to build this boat really easily I would build each section on a concrete floor and simple strongback. No section is longer than 8 foot from front to back. You build each section and then you put it away. Use a kitchen maker to cut out you square cabin fitments.

The hulls would be less essential for accommodation but could still be used for storage. As you need headroom I am guessing that this would only be useful on cats around 40ft.

In the end you would have 5 sections - two hulls and three rigid and strong bridgedeck sections. At the launch site you would bolt and glue all the sections together. If you were really clever you would use a simple moulding that is glassed in like a composite chainplate to hold the sections together so you could undo them if needed - but I bet the thing would stay together once made. Still I have wished I could have pulled my cat apart to work on it somewhere much cheaper than I am forced to got to. The beauty of the sectional method is that each section is a great torsion box on its own and can be built to take the typical cat loads with almost no design compromise.

I know people will say that a pull apart cat would "work" (move and squeak) but you could use the consistent strain from the rig to tighten the whole thing. If designed for it the rig tension would pull it all together so that she would move as little as a normal cat.

I would love to build a square boat that didn't look square. I also love the idea of working on each individual piece on the floor and then stowing it away. My mate paid $6000 bucks to launch his cat and it only had to go 5 kms.

Okay really pie in the sky stuff now - Make it so that you can put the whole thing in two containers - Darling lets go to the Pacific - pull it apart and then you fly over to the boat later.

cheers

Phil
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  #9  
Old 07-20-2009, 06:35 AM
catsketcher catsketcher is offline
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Rig

Gday

I missed your points re the rig

I would not go the twin mast set up - as stated in the above post a normal rig will pre-stress the boat which is a good thing. Many thin and spidery trimarans are floppy without their rigs. Robin Chamberlin and John hitch used a pyramid style beam arrangement that actually used the down force of the rig to stiffen the cats - they were/are very stiff cats.

A twin rig set up is asking for slopping around in a seaway - the forces will act in many different directions - a normal rig will have consistent vectors that you can use to your advantage.

As to pitching - if you are not in marinas you can afford to lengthen the hulls if you make them only for flotation and storage. Hulls are easy to build - it is the fitting out that makes them slow. So lengthen the boat because long hulls will cost very little extra with no interior. You reduce pitching, increase speed, increase carrying capacity and make the boat better looking.

cheers

Phil
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  #10  
Old 07-20-2009, 08:05 PM
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Richard Woods Richard Woods is offline
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As Bill Broome says, I have several designs that suit someone in your situation. For example, I live aboard and cruise my 34ft Romany design during the winters, and that would be a good option for you.

If you look at my Biography pages on my website you will see that it is possible to get a 20ft wide catamaran down a narrow Cornish lane if you try hard enough

Hope this helps, good luck with your boat hunt

Richard Woods of Woods Designs

www.sailingcatamarans.com
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  #11  
Old 07-21-2009, 02:30 PM
ImaginaryNumber ImaginaryNumber is offline
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Nero:
I have looked at the HarryProa site before. What a clever and unusual boat! I have to admit that I've never felt that "spark" that one feels when falling in love with a particular boat or design.

Alan:
Oramís PodCat is an interesting blend of catamaran and trimaran. I like that all the accommodations are kept in the pod, though it appears that the aft bunks are separated from the salon by the cockpit. I wish to keep all living quarters together for ease of heating and access in foul weather.

bill broome:
I have looked carefully at Richard Woods designs. In fact, it may have been from some of his designs that I got the idea of being able to build everything as components. I would be most interested if he were to design a fully segmented catamaran.

Phil:
You clearly understand the concept and appeal of a modular cat with all the accommodations in the bridgedeck! I think being able to build each section in a garage or outbuilding, then storing it outside while working on the next section, would be very appealing to many DIY-builders Ė particularly those who live in colder climates or those who have limited building facilities.

You make an interesting observation that a deck-mounted mast can be used to tighten the components of an otherwise flexible catamaran. I know of a few bi-masted catamarans with free-standing masts that have made significant blue-water voyages. Pete Hillís junk-rigged China Moon made a number of Atlantic transits and sailed well into the Southern Ocean. Bertrand Fercot built a bi-masted Wharram Tiki 30 with Swing-Wing sails, with which he crossed the Atlantic. He liked it so much that his is now building a Tiki 46, again with free-standing masts and a swing-wing sail. Iíve not heard that either had problems with masts or hulls working, but maybe bridgedeck catamaran has different problems.

Bertrand Fercot www.themultihull.com/wharram2/bf9.htm
China Moon http://www.2hulls.com/usedcatamaran-...na%20Moon.html


Richard Woods:
Thank you for your kind wishes. Your Romany is very appealing to me. If my only quibble was difficulty of transporting from build site to launch site it would be less of a problem to solve than presented by your Cornish lane.

But Iím still concerned about heating three separate spaces in cold weather. When you say you winter aboard your Romany in the winter are you talking about Canada or Cancun? Itís Canadian-like winter weather that I need to feel comfortable in. Another disadvantage (to me) of a pod catamaran is that in foul weather one has to go outside to get between the pod and the hulls.

I would really appreciate feedback as to whether the concept of a modular catamaran even makes sense. Are there practical ways to sectionalize a bridgedeck? Are there practical ways to attach a bridgedeck to the hulls? What is the minimum size of the hulls to safely carry a standing-height bridgedeck? Will the extra weight of this type of construction create stability problems? I again emphasize that this would be a cruising boat. Iím willing to sacrifice speed, but not safety.

Thanks to all for your comments and ideas
John
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  #12  
Old 07-21-2009, 08:55 PM
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Richard Woods Richard Woods is offline
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We bought our Romany last year when it was in Virginia. We sailed it to the Annapolis boat show in October and then started sailing south in late Oct/Nov.

We had no heater because I come from the UK and assumed that at a latitude similar to N Africa it would be warm and anyway we were on our way to the Bahamas. But it was cold!!! So we now have a little propane heater for the cuddy (where we tend to sleep when it is too cold for the hulls).

You will see on my Biography page of my website a photo of my first live aboard catamaran under 6in of snow, so I do know what cold is like when living on board!

Yes, you are right, a catamaran is harder to heat than a monohull, but in fact a cuddy catamaran makes it a bit easier as it has three "rooms" On a conventional bridgedeck cat the heat rises so it is hard to heat the hulls (and thus bunk cabins)

You are also right about having to go outside to get from hull bunks to saloon. But on the other hand, you do have a lot of privacy. And as I say on my website, the cuddy catamaran is a very efficient use of space.

I don't think it is a good idea to have hulls that are only used for storage on a cruising catamaran over about 25ft. You don't have THAT much stuff to take (our Romany has loads of empty lockers and underbunk space even though we were living on board for 6 months). And so you'll waste all that hull space. Basically you'd have the same accommodation as a trimaran.

The Flica 34 has very similar hulls to the Romany but has a full bridgedeck cabin. When I drew that boat I realised that many people would not be building near the water. So I drew it so that each hull plus part of the bridgedeck was built seperately. Then the middle section of the bridgedeck (about 6ft wide) was fitted during final assembly. You do need to spend some time by the water, but you can do a lot at home.

It isn't a good idea to make a joint on the boat CL, as that causes problems with, for example, the mast beam and king post. Equally not a good idea to make a joint on the inner bridgedeck/hull as that is where the most loads are. That is why I decided to make the joints midway across the bridgedeck floor.

Does that answer your questions??

Richard Woods of Woods Designs

www.sailingcatamarans.com
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  #13  
Old 07-22-2009, 04:21 PM
ImaginaryNumber ImaginaryNumber is offline
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Richard,

I agree that if the hull shapes were left the same as a catamaran that had in-hull living quarters that there would be a lot of excess space. But if people werenít living in the hull, perhaps the performance of even a cruising catamaran could be improved by making the hulls narrower (and longer?). Could you tell me if narrower hulls would imprudently reduce buoyancy or increase deck slapping?

My vision is to reserve the hull space for seldom-used items Ė like bicycles, a folding boat, and if weight allowed, a small motorcycle or two Ė and to have a full-width and a mostly full-height bridgedeck for the living space. That could give me living space that was perhaps 20í wide by 16í- 18í long. Having the living space all on one level and in a relatively compact shape would make it much easier to heat, and would also be easier for aging bodies to use.

Again, my concern is whether that would put too much weight too high, or whether the increased windage would make control of the boat unacceptably difficult?

You warned against making any connecting joints along either the centerline of the boat, or where the bridgedeck joins the hull. The idea I tried to describe in my first post was to have the bridgedeck sections each span the full width of the boat Ė from outer gunwale to outer gunwale. Catsketcher described it better than I did when he said:

Quote:
1- a full bridgedeck section containing the double berths
2- the bridgedeck cabin
3- the cockpit and aft deck
Ö
In the end you would have 5 sections - two hulls and three rigid and strong bridgedeck sections. At the launch site you would bolt and glue all the sections together ... The beauty of the sectional method is that each section is a great torsion box on its own and can be built to take the typical cat loads with almost no design compromise.
So Iím still wondering if this modular idea for a cruising catamaran is worth further consideration, or whether there are fundamental engineering or aero- or hydrodynamic constraints that make this concept dead-on-arrival?

Thanks for your thoughts,
John
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  #14  
Old 07-22-2009, 04:43 PM
rasorinc rasorinc is offline
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maybe this will generate an idea.http://www.seatrotter.com/
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  #15  
Old 07-22-2009, 05:58 PM
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Richard Woods Richard Woods is offline
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First an aside

Quote:
Originally Posted by catsketcher View Post
Okay really pie in the sky stuff now - Make it so that you can put the whole thing in two containers - Darling lets go to the Pacific - pull it apart and then you fly over to the boat later.
That is something similar to what I plan to do with my 10m Mustang design, only it would all fit in one 45ft highback container.
========================

So really what you are after is a trimaran with the main hull out of the water???

One of my customers recently emailed to ask "Can you design me a catamaran with only one hull?" Clearly he was getting bored with building the second hull

And as I said before, I think once you start building you will wonder "why not make this hull a few inches higher so I can get in it and USE it?" Adding even 12in of freeboard doesn't add much to weight (certainly less than a couple of motorbikes). And the extra freeboard and thus windage doesn't seem to slow boats down a great deal, especially when the hull freeboard breaks up the "boxy" main cabin.

Then you end up with, say, a Romany. Which otherwise has all the advantages you list. My 40ft version, the Rhea, has a big enough cuddy to fit in the heads/shower as well. One great advantage of the three compartment concept is the fact that there is lots of privacy. Another is that it is easy and safe to go forward as the side cabins act as bulwarks, whereas your proposal doesn't even have sidedecks (if I understand you right)

What you are proposing is nothing new. Eric Manners built several like that in the early 1960's, while Prouts built a 40ft boat, Phantom Wake, in the late 1970's (I think) with accommodation only in the central cuddy. I did the same with a 45ft cat in the mid 1980's (the hulls are made but it is still unfinished). The early CSK boats like the grp Polycon, still for sale in various places, were really very similar although you could get in the hulls.

Having said that it is clear that such a boat isn't a popular concept, so not quite DOA but close. It maybe your ideal boat, but I find most people come to sell even their "ideal" boat sooner or later and if the concept itself isn't popular then the chances of you selling your boat for anything like what you pay for it are slim. And that alone would be enough for me to advise against doing it.

Sorry to be so negative, but build it and prove me wrong.

Richard Woods of Woods Designs

www.sailingcatamarans.com
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