Argo the Modular Pod Cat

04 October 2021     Editor    25 Comments.

Well here it is late 2021. The world has been in a COVID-19 mess for 18 months, with no real end in sight. Global supply chains are a complete train wreck, and it’s not looking to change anytime soon. Prices of lumber, especially plywood, have skyrocketed, along with most everything else related to boat building. Back in the day, when so many plywood classics were designed and built, good marine plywood was a very reasonably priced boat building material. However, over the decades it has gone down in quality as much as it has gone up in price and the latest price jump got me to thinking… is plywood now so spendy that other building materials are becoming competitive… like fiberglass?

Classic plastic has the magical ability to conform to any shape you could desire, but the Achilles heel is that it needs a mold, which is like building the whole boat all over again. That is why molded fiberglass is a process best suited for mass production. Unless…

ARGO MOD-FAB

What if we created a simple set of molds that could combine multiple functions, using an optimal design that cuts down on surface area and thickness needed in most areas and could be reinforced locally (crash areas in bow, keels, shroud bases, beam sockets). We know that an elliptical section is the best compromise between ultimate strength and space. Curved surfaces add strength without weight. Think of an egg - all curved, with a thin shell.

Argo is a modular system of fabrication that allows for a wide variety of configurations. The catamaran is made from just two simple molds - each about ten feet in length. Both molds would easily fit inside any garage, or storage unit, or a 20’ container workshop…

The body of the hull is an elliptical tube section, like a Boeing. The bows and sterns are identical, and are also identical top to bottom. You’d make a molded part for the bottom, and make another one, and then turn one over and bond them together at the gunnel. You’d need a half tube mold, and a half bow mold, and that would be it. The pod is made from the same hull molds, plus some extra flats, etc.

You would need 8 bow parts and 4 body parts for the two hulls, plus 3 body parts for the pod. It is mass production on a personal scale, and it makes spending time on the molds worth it. In exchange for the molds, you get a real fiberglass boat, with all the attendant virtues of the material:

  • A gelcoat gloss finish w/ virtually no sanding or painting
  • Ideal hull sections
  • Practically impervious to decay*
  • Good resale value

The modular fabrication system encourages a variety of applications:  from sail to power, from private adventure yacht to water taxi, fishing boat or charter dive boat.

ARGO 1

Argo 1 uses a 5’ high x 4’ wide hull section.She is a 30’ ocean voyager, though she can go longer, up to 40’ if required - just build an extra middle section. She is not designed for top speed, though I think she will be no slouch, especially in the trade winds for which she is meant. She is designed for load carrying because - have you ever seen a small cruising cat that is really out there doing it, that floats on its lines? Me neither.  Argo is a capable load hauler.

The catamaran would be built in three large sections - two hulls and central cabin. Her slender hulls with a 9.4:1 L/B ratio are easily driven, allowing a modest sail plan of 440 sq. ft. The sail area to displacement ratio of 20 places the boat slightly above a Cal 40 and well below a Farrier trimaran, but hull flying isn’t really on the agenda.

The central pod houses the galley, eating area, general social space, navigation and solar panel energy systems. The dinette converts into a large double berth. A pop-top provides generous standing headroom. Plenty of storage too.

The hull interiors are kept as simple as possible, with three bunk flats and a composting head compartment. The bunks are 7’ long x 3.5’ wide, which isn’t half bad for a 30’ cat. Fore and aft of the sleeping cabins are generous storage lockers, and fore and aft of those are sealed crash box areas. There are no thru-hulls.

The 5’ of headroom is plenty for sleeping, and the low rounded shape of the roof offers minimal windage and wave resistance. I have cut away the fore and aft sections to make a flat deck to walk on, but that is not strictly necessary for the concept.

Cross beams would all be made from used (oversize) mast sections for low weight, minimal maintenance, and simple construction. The finest place to be on a catamaran is the bridge deck, and Argo 1 has loads of deck space. Decks to fish from, sunbathe, stow a dinghy or crab pots, or maybe just to throw a party. The “walk-around” design of the pod gives excellent access to anywhere on the boat, bow to stern.  There is a boarding ramp forward to gain access from the beach or the water. A pair of deck boxes aft provide seating and storage, and I’ve drawn an easily stowed boom tent to set up at anchor.

Argo 1 is a serious cruising catamaran, not a racer, which means sturdy low-aspect ratio keels. No vulnerable daggerboards, no slots taking up cabin space, no moving parts, no worries. Also, no line honors in a race to windward, but gentlemen never sail to windward anyway! I have drawn up two rudder arrangements: one is a high aspect-ratio blade, variable depth, kick-up affair. The other is a short skeg rudder no deeper than the 2.4’ draft keel. The skeg rudders create a four point suspension system with the keels to permit safe and simple beaching. The deep blade rudder is the better performer, until you hit something. At least a catamaran always carries a spare rudder in the other hull.

Another cruising design decision is the rig. You don’t often see gaff-rigged cats these days, however, the gaff is simply a better performer off-wind than the lofty Marconi. The lower center-of-effort reduces heeling and overturning moments, mast height lowers, demands on the shrouds lessen, you don’t need to luff-up to reef or hoist**, and down the design spiral we go. I’m thinking a used sailboard carbon mast might do for the gaff.

ARGO 2

Argo 2 is a mod of the pod into a resort-style excursion boat - the type tourists rent for a 3 hour tour. The big hardtop provides shade and solar power, while underneath is some seating and refreshments. A clear vinyl and canvas enclosure could make the pod habitable enough even in a rain squall. The raised helm station aft gives the captain a commanding view. The outboard lives directly beneath the helm station module. The gaff rig has been swapped for a square-top main because this boat will probably see a lot of windward sailing and besides, it’s a business expense.

MEA CULPA

Argo is an intriguing concept but there are still many questions. What the actual fiberglass layup will be and what it will weigh is just one among many. How will the molds be constructed? What about the keels? Just how much is this dang thing going to cost anyway? I don’t have the answers to that yet. Let me know what you think in the comments. What about ARGO 3?

THANKS

A great deal of thanks to the Argonauts who have provided their time and insights to the project: Paul Cheevers, John Dalziel, John Pugh and Robert Wise.

———————

Note: ASSOCIATION DES RECHERCHES GLOBALES OCÉANIQUE is not a real NGO, but it should be.

* Yea, that’s an exaggeration, but compared to wood, especially to indifferently maintained wood, it’s true.

** So says sailing legend Paul Johnson.

 

 New Designs  Catamarans

25 Comments

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  • Congrats Michael. Looks like it is all coming together now. Looking forward to hear what the experts come up with regarding layups.

    2021-10-05 17:34 | by Paul Cheevers

  • Michael, this new design is a package of visionary ideas that has made me re-think my approach to boat building and the materials I use. As you point out there are obstacles to overcome but the overall elegance of your modular concept and visually stunning design is a grand example of the best of your work. Kudos.

    2021-10-06 09:46 | by Neal Sarras

  • Looks like a great new concept to fill my boatbuilding daydreams.  I’m eager to hear more as the vision unfolds!  Thanks!!

    2021-10-06 22:26 | by Jonathan Morse

  • Wow.  Another thoughtful re-ordering of the design constraints by Mr. Schacht.  I absolutely love this.  I wonder if you can have a gel coat finish. I’d want mine to have some long fibers in the outer shell—rather than just bonding together the pieces.  I’d sheath the bonded up shell on the outside with cloth to get those long fibers from bow to stern.  That could also provide an epoxy coating to block moisture from the more economical vinylester laminates inside.  The big question with the shell sections is what core materials makes sense.  Solid sections are too heavy (or too flimsy). Rather than making the deck flats, you could make a mold that adapts a flat off the shelf hatch to the elliptical skin—sort of a blister with a flat top.  For cross beams you might consider pultruded fiberglass.  A friend of mine used these on the L7 Trimaran because you can order a section based on engineering calculations—and they are dirt cheap compared to basically everything.  And you can bond to them.  Bravo, Michael.  Very cool.

    2021-10-07 14:17 | by Chris Luomanen


  • Thanks for the kind words, everyone. I’d love to hear your ideas on the subject and really encourage comments. This is most definitely a work in progress.
    Chris: I was planning on running long fibers, if not stringers, inside the hulls once assembled, but all ideas are on the table. I especially like the pultruded fiberglass beams, I remember that L7 tri.

    2021-10-08 11:36 | by Editor

    • You could run long fibers (in cloth) inside but you'd have to do it before you put in bulkheads. Are they in a cradle? Stinger are another idea--but they won't bond the entire joint. The biggest stresses in an object travel along the outer surface--so putting those long fibers on the outer surface--and having them everywhere along that outer surfaces should produce big benefits in strength and the sharing of loads. So maybe you don't get the perfect gel coated surfaces out of the mold, but at least there is very little fairing when you do have to sand. Vacuum bag the whole thing with peel ply and you won't even have any drips! Still really digging this, Michael.
      2021-10-19 14:58 | by Chris Luomanen

      • Thanks for your ideas, Chris, much appreciated! I'm going to be building some models with various fabrication concepts, it should be both fun and informative. I think bagging it will really help improve the quality of the parts.
        2021-10-20 19:13 | by Editor

  • Would full length internal stringers help with the long fiber question? They could be placed at bunk height and along the floor. Also I imagine that the top and bottom sections would be joined internally from bow to stern as well as vertically between the sections.

    2021-10-08 15:39 | by Paul Cheevers

  • Check out the composite construction of the Boeing 787 fuselage it will give U lots of ideas.

    2021-10-09 00:17 | by Kenzo

  • Better with a Wharram style gaff?
    Those stern will drag, need to be slightly above the water at standstill

    2021-10-09 08:36 | by Mark Thomasson

    • I've built a Wharram Tiki and the small gaffs really do not have the advantage of a longer gaff shown in Michael's drawing. As far as the wing sail element of the Wharram rig goes I did not find it any better than the same sail area without the wraparound.
      2021-10-17 07:55 | by RLW

    • Living in Port Townsend, we see a lot of old gaffers, and even some brand new ones, so it doesn't look that out of place to me. The gaff has some advantages for cruising - but the Argo concept is all about flexibility, and if you want a Marconi sloop or even a Chinese lug, then there is no reason not to have one, we just need to make sure the CE is in the same spot, more or less. Sterns: The only time I have ever seen a cruising cat without dragging sterns is at the launch party when it is empty. Might as well plan for it. Once the boat is up to speed, the wake will leave the transom cleanly.
      2021-10-17 12:04 | by Editor

  • I’ve thought along similar lines using large diameter pipes, maybe fibreglass or hdpe especially if you could find pipe you could shape by heating areas and deforming them.

    2021-10-13 21:00 | by Tedward scizzers

    • https://www.youtube.com/watch?v=TiVGiIs_57o. Try this.
      2021-10-17 15:29 | by Paul Cheevers

  • I met a tri on the south coast (UK) a while back.Itwas entirely made of pipes. A huge diameter one or the hull, smaller for the amas, much smaller for the beams.It looked quite racy and very different. It was called ‘PipeDream’.Probably sailed well but looand fun to make.ked decidedly uncomfortable. Argo a huge improvement and fun to make.
    Dimensions and overall scheme much like a Woods Gyps, which I have.
    Much lok forward to seeing the finished design and construction.

    2021-11-05 02:56 | by Mike

    • That's the trimaran "SV Pipedream", built by Robert Dyer in the mid-1990s. He was in his early 20s at the time. The main hull had originally been a steel cooling tower, used at a Welsh hospital. Robert has a Youtube channel, which contains several videos about the project: https://www.youtube.com/channel/UC1PuwBQgM9H1w9yhz-UbTFg At the following video, the first minute recaps the story of the "Pipedream": https://www.youtube.com/watch?v=naJiowoi6hU During the time Robert was constructing the "Pipedream", it garnered quite a bit of press attention. I'm in New Zealand, and remember seeing a BBC news story broadcast here, showing it being taken down the Thames, prior to it being fitted out. This would have been circa 1997-98. Here is a link to a subsequent BBC news story, one which shows the "Pipedream" when it was fully completed: https://www.youtube.com/watch?v=l8Yr5eShenI Robert still owns the trimaran. It's currently on the dry, in a boatyard in France; the bow and keel have undergone some revision in recent years, this being done in order to improve the craft's handling.
      2021-11-12 23:33 | by Aerohydro

  • Great color renderings, exploded views and overall presentation of
    the concept.  This could be a good approach to manufacturing if done
    right.  Best!

    2021-11-24 19:01 | by Mark S Palmquist

  • I’m a nobody, so you can blow me off, but I wanted to ask, what is
    the fixaction with gel coat? I get less friction, but given the
    multiple joints, there are still going to be plenty of glassing, fairing,
    and then top coat.  I guess I’m seeing less advantage to the time to
    prep a mold so smooth you use gel coat over just a final fairing job
    after the splicing and then paint it.


    I recently watched some video of a guy who simply designed some
    one off cats on a piece of paper.  He built a ‘house cat’ with more
    the dimensions I think would work for this.

    I do like the way you can just make the modules and then piece
    them together. What was the reason for choosing only 5’ tall over
    say two matched 3.5’ or 4’ shells’ with a more suitable beam like 6-
    7 feet, making those interior spaces more functional I mean,
    submarines have a similar hull shape and they do fine?

    One thing some of the comments about structure made me think
    about was what if you made the hull sections with a lip, much like
    you see in the pipes and tube of a waterpark, where they connect
    the top and bottom sections with bolts.  In fact, this makes me
    want to purchase some sections of waterpark slides this summer
    and see if I can’t make a smaller cat with those and a cone section
    mold for the ends.

    Also interested in the dimensions of the ‘deck pod’  the overall
    beam only at 18’, less two pods 4’ wide and then lets call it 18” on
    each side to walk around as you say, and that is another 3’ and you
    are down to less than a 8’ wide pod,  and then 10’ long, or 80ft2, not
    a lot of space for all you envision in a “ocean voyager”. That’s likely
    resolved with widening the beam to more like 24 and going to 32-
    34ft LOA.

    Like I say, I’m a nobody, I just thought I’d toss out a brainstorm.

    One thing I really also like is the potential here for something like a
    Harryproa.  This design could be a real proa if you added a rudder
    plan like he uses.

    2022-05-30 03:53 | by Trent Lamb



  • elegant concept,  Doesn’t look like its self righting

    2023-11-14 05:57 | by Dean

  • So, I know I’m late to the party (also I’m too poor to do any of this) but I find
    this interesting as it has the potential to allow for constructing a floating
    shipyard that can make more floating shipyards (and obviously ships) since
    each part is modular. It would be a interesting concept for a community fleet
    of ships. (Especially if a ship could be partially disassembled for work to be
    done on it during transit.)

    Anyway, amazing work. I wonder what a scaled-up version would look like
    (one designed for long-term / permanent living / shipyard) larger hulls vs
    more hulls and the difficulty of detaching hulls for maintenance in addition
    to how to plan redundancy, as well as what modifications would need to
    happen for it to have electric self-sufficiency with electric engines.

    Again, this is a amazing base that can be built off of in so many ways, and
    much better than many of the back-of-a-napkin ideas I have had over the
    last year or so.

    2023-11-30 04:29 | by J. Cline

    • Thanks for the comment, and for your taking the modular ship building process in a direction that you imagine. That is really what the design spiral should be about.
      2023-11-30 21:26 | by Editor

  • I am very interested in this type of boat for cruising the florida coast, the keys
    and possibly the Caribbean.  Can I get more information on the molds,
    construction process and cost please?

    2024-05-11 22:39 | by David