A 20 foot cruising catamaran

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  • slidercat
    Senior Member
    • Jul 2008
    • 808

    #16
    Re: A 20 foot cruising catamaran

    Chip, it's a folding cat with accommodations in the hulls, so there really can't be any cabin on the bridgedeck. The center deck is in two sections, hinged along the central spine, so they lift up and can be bungied together for folding.

    The dinette is almost 5 feet long, so you could squeeze 3 or 4 folks in for dinner. You'd have to put the shortest person in first, since headroom drops forward. The navigator will have to chart at the dining table, but it could be worse, I suppose. I'll put up some drawings of the port hull in a day or so, which may make matters clearer.

    With a cat this small, I think you really have to be disciplined as to what is actually necessary for a short passage. Otherwise you might wind up with a heavy monstrosity that doesn't sail well. I really wanted a built-in icebox, but I don't think it's in the cards.

    With a wide beam cat, there's a lot of room to spread out, when not on passage. I imagine a deck awning and some folding chairs and table would add greatly to comfort at anchor. Slinger's center deck is almost 5 feet across, and 10 feet long, so there's circulation.
    Ray

    http://slidercat.com/blog/wordpress

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    • slidercat
      Senior Member
      • Jul 2008
      • 808

      #17
      Re: A 20 foot cruising catamaran

      Just a couple quick sketches:



      And a section through frame #3"



      Details here.
      Ray

      http://slidercat.com/blog/wordpress

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      • 62816inBerlin
        Landlocked in Berlin
        • Feb 2008
        • 805

        #18
        Re: A 20 foot cruising catamaran

        I like your idea - have you published details of the folding arrangement?

        Perhaps you should discuss the internal accommodation arrangements with Tony Bigras, who travelled a great distance in a 16´cat, including crossing from Central America to Cuba and on to Florida (see http://turtleislands.net/tmc/default.html)



        I suppose someone who has lived aboard for so long would have some tips about what to avoid and what must definitely be observed when building a vessel of this kind.

        Gernot H.
        Last edited by 62816inBerlin; 02-03-2011, 04:36 AM. Reason: I really should turn on the English spelling checker!

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        • Dan St Gean
          Senior Member
          • Nov 2004
          • 1138

          #19
          Re: A 20 foot cruising catamaran

          That'll work. Lots of small cats do it that way. I'd have some largish windows so you don't feel so claustrophobic while eating.

          Dan

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          • slidercat
            Senior Member
            • Jul 2008
            • 808

            #20
            Re: A 20 foot cruising catamaran

            Thanks, Gernot.

            I'm being secretive about the folding mechanism, because I haven't seen it before, and I'm looking into whether or not it's patentable. I hate to do that, because it makes me feel like a jerk to be using the forum as a sounding board without letting everyone in on a crucial element of the design. But I can say that it's a variant on the kind of mechanism that folds at the hulls and at the central spine.

            Isn't Miss Cindy a great little boat? When Tony was on his big sail, I checked his blog every day, to see if there was a new update.

            Unfortunately, Miss Cindy is a completely different approach to the tiny cat problem. Tony made her with a fixed beam of 8.5 feet, so she could be transported easily on the American highway system. He put that low aspect biplane rig on her so that he could get 200 sq. ft. of sail, but still keep the center of effort low. Because he had fixed beam (no folding) he could use a bridgedeck cabin.

            Slinger will still have to be 8.5 feet for trailering, but she has a high aspect rig of 220 sq. ft. I had to figure out a way to fold her out to a wider sailing beam, which precludes having a central cabin. Richard Woods has designed some very clever folders that do have central cabins, but they have drawbacks for my purposes. One is that all accommodations are in the central hull. Another is that the boat cannot be folded with the rig up for narrow slips or dry sailing. One of the things I'm trying to accomplish with Slinger is a catamaran that's as easy and quick to fold as a Farrier trimaran. A couple of Farriers live on the canal across from my house, and their owners keep them out of the water in slings, rig up. Every time we take our little beachcruiser Slider out, we paddle past these boats, and I am fascinated. When the owners want to go out, it doesn't take them much more time to lower their boats into the water and fold out the floats than it takes us to get aboard and cast off.

            Dan, you're right. You can see the windows in the frame sketch, if you look close. Down here in the sunny semi-tropics, it's a balancing act for windows. You want the light, but not the heat. I think I'll err on the side of more light, for the very reason you suggest.
            Ray

            http://slidercat.com/blog/wordpress

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            • Dan St Gean
              Senior Member
              • Nov 2004
              • 1138

              #21
              Re: A 20 foot cruising catamaran

              Originally posted by slidercat
              Thanks, Gernot.

              snip--comments in bold

              Isn't Miss Cindy a great little boat? When Tony was on his big sail, I checked his blog every day, to see if there was a new update.

              Unfortunately, Miss Cindy is a completely different approach to the tiny cat problem. Tony made her with a fixed beam of 8.5 feet, so she could be transported easily on the American highway system. He put that low aspect biplane rig on her so that he could get 200 sq. ft. of sail, but still keep the center of effort low. Because he had fixed beam (no folding) he could use a bridgedeck cabin.

              A nice solution to a vexing problem. His cruise really made my winter speed by...

              Slinger will still have to be 8.5 feet for trailering, but she has a high aspect rig of 220 sq. ft. I had to figure out a way to fold her out to a wider sailing beam, which precludes having a central cabin. Richard Woods has designed some very clever folders that do have central cabins, but they have drawbacks for my purposes. One is that all accommodations are in the central hull. Richard has some add on cabin tops that remedy that issue. Another is that the boat cannot be folded with the rig up for narrow slips or dry sailing. I'm sure that could be dealt with using a baby stay and inner sidestays. One of the things I'm trying to accomplish with Slinger is a catamaran that's as easy and quick to fold as a Farrier trimaran. A couple of Farriers live on the canal across from my house, and their owners keep them out of the water in slings, rig up. Every time we take our little beachcruiser Slider out, we paddle past these boats, and I am fascinated. When the owners want to go out, it doesn't take them much more time to lower their boats into the water and fold out the floats than it takes us to get aboard and cast off. I'm wondering if one of Woods' folders couldn't deal with the folding in a similar manner--using a liftunder the bridgedeck if width is an issue. Still, I'm looking forward to seeing your build and solution to a vexing problem.

              Dan, you're right. You can see the windows in the frame sketch, if you look close. Down here in the sunny semi-tropics, it's a balancing act for windows. You want the light, but not the heat. I think I'll err on the side of more light, for the very reason you suggest. You can always meet in the middle with tinted glass allowing the view without the heat.
              Good conversation! I am enjoying where you are taking this little cat. A very different solution than Richard Wood's latest small cat Acron. As an aside, which Jones cat did you use to estimate your beams from?

              Dan

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              • slidercat
                Senior Member
                • Jul 2008
                • 808

                #22
                Re: A 20 foot cruising catamaran

                Dan, I guess one of Richard's folder could be modified to keep the rig up, but most boats kept in slips must be antifouled. The way the hulls fold, if I'm remembering correctly, is that they rotate until horizontal. They'd grow a lot of barnacles on the topsides in my canal. That's why the Farrier owners have their boats up in slings. I'm trying to devise a system where the hulls stay upright. If you don't mind the hulls tipping on their side, Thomas Firth Jones has a nifty little cat, too. Brine Shrimp folds upward in the middle.

                I should hasten to add that this is no criticism of Richard. As far as I'm concerned, he is the foremost designer of small cruising multis in the world today. I wish I had even a fraction of his talent and experience.

                I think I will use tinted plexiglass. It does cut down some on the heat, though not as much as you'd hope. The main objection to tinted portlights is that they give a sort of gray cast to the scenery.

                For Slider, I used the beam scantlings of Jones' Weekender. For Slinger, I'm using box beams, which Jones did not use in his designs. I fear my box beams will be massively overbuilt, since I'm also using them to get flotation in the right place for a capsized cat. I hope never to have to test this flotation, but it would be foolish to ignore the possibility of capsize offshore.
                Ray

                http://slidercat.com/blog/wordpress

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                • Dan St Gean
                  Senior Member
                  • Nov 2004
                  • 1138

                  #23
                  Re: A 20 foot cruising catamaran

                  Ray,

                  On a week trip on Gilbert & Sullivan a 36' modified Tourissimo 10, the builder had matching homebuilt ice chests. He used thinly glassed ply with 4" of rigid insulation. With preprepared meals frozen along with some frozen water it lasted the whole week cruise. You could easily do smaller ones on either side of the mast on the flat hard deck. Its not as handy as being right next to the galley, but you don't want to open it much anyway. Once a day for the big chest and another for daily use works well.

                  Dan

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                  • 62816inBerlin
                    Landlocked in Berlin
                    • Feb 2008
                    • 805

                    #24
                    Re: A 20 foot cruising catamaran

                    Originally posted by slidercat
                    Thanks, Gernot.
                    Hi Ray,
                    I'm being secretive about the folding mechanism, because I haven't seen it before, and I'm looking into whether or not it's patentable......
                    I fully understand your situation.
                    Ever since I sailed on a shakedown day outing with Jim Wharram on his original "Rongo" I have been a fan of catamarans and crewed on Shearwaters as a teenager. Since then my only hands-on experience is limited to a few hours' sailing a rented Hobie in a raging Mistral (30 years later) on the Mediterranean coast of France and a cruise on a party catamaran around San Francisco bay and under the Bridge.
                    Limited docking space, unfortunately, makes owning a cruising catamaran problematic in Berlin which is why I have stuck to monohulls. A folding version that can be rigged up quickly and still has enough room to keep the best wife of all times (as Ephraim Kishon would say) happy would be great for messing about in the local lakes, rivers and canals, being "beachable".
                    A relatively low aspect rig would also be an advantage in the sense that there would be less problems with a lowered mast when passing through locks and under bridges, which is why I was taken by Tony's idea. Unfortunately, unstayed masts do not go well with a folding arrangement.

                    I wish you much success, keep us informed and post lots of photos!

                    Gernot H.
                    Last edited by 62816inBerlin; 02-04-2011, 04:33 AM. Reason: slight addition to text.

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                    • slidercat
                      Senior Member
                      • Jul 2008
                      • 808

                      #25
                      Re: A 20 foot cruising catamaran

                      I've refined the design a bit more, in the incremental manner I like. One big issue that I was unsatisfied with was the seating on deck for the helmsman. At one recent point I's settled for the approach recommended by Thomas Firth Jones, which was for the helmsman to sit in one of the companionways.

                      But I was dissatisfied with this for a number of reasons. Finally it occurred to me that a couple of removable seats would do the job, and could serve also as removable ice chest and cockpit stowage.

                      Here's an updated plan view, with the removable seats in pink:



                      Here's a section, to make the idea a bit clearer:



                      Here's a post on the design process that led to these ideas.
                      Ray

                      http://slidercat.com/blog/wordpress

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                      • Dan St Gean
                        Senior Member
                        • Nov 2004
                        • 1138

                        #26
                        Re: A 20 foot cruising catamaran

                        Looks good Ray! Keep cracking at it. I got after the beam and attachment for my Tamanu today. Main beam laminated, MDO beam attachment plates cut out and a plan for the aft beam hatched.

                        Dan

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                        • Dan St Gean
                          Senior Member
                          • Nov 2004
                          • 1138

                          #27
                          Re: A 20 foot cruising catamaran

                          Yeah I'm replying to myself... I forgot to mention something though. You could easily do some of those folding chairs available with the ratcheting backs and sunbrella covers to both raise the backrest and give a nice cushion to the bum.

                          Dan

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                          • slidercat
                            Senior Member
                            • Jul 2008
                            • 808

                            #28
                            Re: A 20 foot cruising catamaran

                            Dan, that's a good idea. Sometimes we put a folding chaise lounge on Slider, though not for the helmsman, because the steering line runs around the outside perimeter of the cockpits.

                            The new boat will have a central tiller attached to the linkage bar, so it's within easy reach of either seat. I've thought about those little stadium seats atop the ice chest and cockpit locker-- the cabin side is inclined at the right angle to support them.
                            Ray

                            http://slidercat.com/blog/wordpress

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                            • paladin
                              Senior Senior Member
                              • Dec 2000
                              • 26476

                              #29
                              Re: A 20 foot cruising catamaran

                              The central spine beam will need some bow in it and a bit more structural integrity. Make the hulls a little farther apart, cant the hulls outward 7-8 degrees and reinforce the edges of the craft to hold clamps/fasteners for the net. Take a close look at Jim Browns wing folding system.
                              Wakan Tanka Kici Un
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                              Fighting Illegal immigration since 1492....
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                              • slidercat
                                Senior Member
                                • Jul 2008
                                • 808

                                #30
                                Re: A 20 foot cruising catamaran

                                Good suggestions, but the central spine is a box beam, more than strong enough to withstand the thrust of the mast. Because the bridge deck has almost 30 inches of clearance, the central box beam can extend well below the decks without too much concern for wave impact. It has to be over-engineered, because it carries the forestay-- a necessity given the design goal of being able to fold the boat without taking down the rig. This is to facilitate dry sailing, and parking the boat in a narrow slip. I believe a small protective nacelle for an outboard can be engineered at the aft end of the spine.

                                I'm not a believer in canting catamaran hulls outward, though that works very well for tris. It may well be a good idea, but it wouldn't work well in this case, due to the folding arrangement I've devised. This arrangement also limits the maximum beam, unfortunately, so it couldn't be adapted to much larger cats.

                                Jim Browns trimaran folding scheme is very clever, but not applicable here, because of the cabins, which project above the center deck, so that the hulls cannot be folded under the central deck, as the floats of Jim's new tri are. I'm also using hard decks, which are a lot more comfortable for cruising than tramps, in my opinion.

                                That said, I have to admit that it was his 20 foot Seaclipper that got me thinking about this design. He had a lot of sensible things to say about little multihulls, and the possibility of recycling beach cat rigs. In a way, my new cat is an attempt to show that small cats make better cruising boats than small tris. If you want to compete with someone, why not compete with the best?
                                Ray

                                http://slidercat.com/blog/wordpress

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