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Thread: A 20 foot cruising catamaran

  1. #51
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    Default Re: A 20 foot cruising catamaran

    Shaping a ply box with glass over foam has been done for 20 years or more. It has its points, but in small boats you do loose interior depth that is usually wanted. Someone circulated plans for a dinghy built like that sometime back, with the added sales point that it was unsinkable.

  2. #52
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    Default Re: A 20 foot cruising catamaran

    Ray i have also considered doing a stripper hull in foam core. Mainly because it is super light and far less work than milling and fitting cedar strips. But the cost of the foamcore material is prohibitive, far more expensive than even wrc. Do u have a good source for the foam strips, or is that just the cost of a superlight composite boat? Haha for all the nostalgia it seems sometimes a wood boat is the cheapest way to build a boat one off even today!
    “The difference between an adventurer and anybody else is that the youthful embrace of discovery, of self or of the world, is not muted by the responsibilities or the safety-catches of maturity.” Jonathan Borgais

  3. #53
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    Default Re: A 20 foot cruising catamaran

    Quote Originally Posted by peterchech View Post
    Ray i have also considered doing a stripper hull in foam core. Mainly because it is super light and far less work than milling and fitting cedar strips. But the cost of the foamcore material is prohibitive, far more expensive than even wrc. Do u have a good source for the foam strips, or is that just the cost of a superlight composite boat? Haha for all the nostalgia it seems sometimes a wood boat is the cheapest way to build a boat one off even today!
    Peter, I use a lot of foam core in my shop. I'm not sure what you are paying, but feel free to contact me about my sources and prices. Scott

  4. #54

    Default Re: A 20 foot cruising catamaran

    Peter, my knowledge of foam construction is pretty much zero. I think I have to agree that plywood is still about the cheapest (and fastest) way to build a one-off boat. I'm planning to use some cheap non-structural foam to add flotation to my center decks, but that's different from building a hull.

  5. #55
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    Default Re: A 20 foot cruising catamaran

    I've priced 2" thick transom foam that would be appropriate for the computer-generated cross sections that I would like to add to the flat bottoms of my dory styled catamaran hulls but found it to be quite pricey. Scott, I'd be interested in hearing about your source for marine foam as someday I'd like to play around with the stuff. As I said I'm in the middle of renovating my cottage so no time for boat building and no money for it either right now but soon as I have a functioning kitchen I'll be back at it again. And then as a retired guy on a fixed income, I'll have more time than money so the idea of making a flat bottomed boat round bottomed from scrap 2x white pine or spruce has its appeal even with the weight penalty. The dory catamaran hulls that I've built weigh very little as they are now so they could probably afford to gain some mass especially down low on the bottom. For my hulls, I'm not talking about a lot of material anyway – just enough to soften the chines and therefore the cross sections of the bottom. The sides I would not touch. Another added benefit for me is that the little wooden cross sections that I would be adding to get a more rounded bottom could get their final shape from my power planer so the transitions from one chunk of wood to the next would not have to be perfect. By measuring the before and after performance of the hulls, if the lighter flat bottoms performed better than the heavier more rounded ones, I could just plane off the dead wood cross sections that I had added and return nearly to the lighter flat bottoms that I had started with. Us old guys need to keep ourselves entertained.

    Scott, I think you owe me a welcome back to St. Augustine beer.

    Ray, you should trailer Slider over here as it would be a great excuse for me to take a break from all this house renovation and just go sailing.
    Last edited by kenjamin; 02-22-2011 at 07:36 PM.

  6. #56

    Default Re: A 20 foot cruising catamaran

    On the whole flat bottomed vs. round bottom front, I came across some speculation on Richard Woods' site that struck me as interesting. He has designed some dory-hulled boats, and seems to feel that they are pretty fast. Anyway, at the bottom of his FAQ page there was this:

    "So my first surprise was that the WL beam of the hard chine hull was less than for the round bilge hull, hence the LWL/BWL ratio is higher/faster. Much more surprising was the fact that the wetted surface area was essentially identical, and WSA is of course the main factor affecting low speed drag.

    So the implication is that a chined hull will have similar speed to a round bilge hull in light winds, and be faster in a blow. "
    I greatly admire Richard's designs, so I pay attention to what he says.

  7. #57
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    Default Re: A 20 foot cruising catamaran

    If the Acorn was out when I started building, I'd be on that boat this summer. Assembling a boat like that at the ramp soen't sound fun though.

    Dan

  8. #58
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    Default Re: A 20 foot cruising catamaran

    Scott, I think you owe me a welcome back to St. Augustine beer.
    I bought you one, but then drank it while waiting for you to show up. Give me a ring. My number is on the contact page of my website, www.seaworthysolutions.net , Scott

  9. #59
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    Default Re: A 20 foot cruising catamaran

    On the whole round bottomed add-on idea, I wonder if some reinforced Dow foam would do, glassed like a surfboard? Wouldn't weigh as much as solid wood I imagine, although the amount of glass that would be needed to reinforce that soft foam may make up for the weight savings... I suppose WRC wouldn't add too much weight, if an arc-bottom would suffice...
    “The difference between an adventurer and anybody else is that the youthful embrace of discovery, of self or of the world, is not muted by the responsibilities or the safety-catches of maturity.” Jonathan Borgais

  10. #60

    Default Re: A 20 foot cruising catamaran

    I've pretty much finished lofting the new boat. This is my lofting table:



    I'm lofting at half scale.

    I've still got a few measurements to take and then I can start cutting patterns and putting together the strongback. The actual lofting of a hull this simple takes an hour or two, but figuring out where to place all the frames and stringers to make the internal fitting out as uncomplicated and light as possible takes a bit longer. As is my habit, I left a couple framing decisions to the last minute.

  11. #61
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    Default Re: A 20 foot cruising catamaran

    Looking good Ray! Keep cranking on it. Do take the time to figure out where the optimal bulkhead & stringer placement will be as it will save huge amounts of time later in the build. After building the decks on my Tamanu hulls, I now want to have a slightly different beam attachment method and am now forced to work through a hatch or worse, rip off the deck. Actually, ripping off a tiny bit of deck in the area of the beam location wouldn't be that bad... like you I like to mull over the design ideas a bit.

    I'd rather build to plan, but when there's no plan for what you want to build, you 'gotta improvise a bit.

    For example, I love the look of Richard Woods new acorn design & would have built it if it was available when I was building. However, I'm looking for a trailerable width and a hard deck aft, so even that really nice design isn't quite "perfect" for my needs. Which is also why you're designing such a different multihull....

    Ironically, I am closest in design to a 1959 design called the Pacific catamaran blended with a Hobie 21SC. It's fun fooling with it though, but with small kids I gotta say it seriously cuts into available building time (as does a cold garage & the need to totally clean up the school's shop if I use that).

    Press on man!

    Dan

  12. #62
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    Default Re: A 20 foot cruising catamaran

    Quote Originally Posted by slidercat View Post
    ............. I guess it's been done in beach cats, but I think they had support vessels, though I could be wrong. Of course, a big problem would be that I'm starting on the wrong side of the pond for an easy passage. .............
    Yes, it's been done, see : http://www.sail.ie/misc/cats_atlantic.htm

    But I quote:
    >>>>>. Pradel's feet, which had seldom been atop the wings and were always submerged in salt water, were just tattered flesh. The skin was torn away over most of their surface. Laurent had deep wounds and scars over his butt and thighs as well as craters on his feet a millimetre deep. Both men's hands were covered with wounds that had crusted and would not heal. Each cut, which never had a chance to dry and heal properly, was infected. Their circulation suffered the effects of blockage due to sitting and crouching in one position for hours on end and their hips and knees were paralyzed. Every movement brought tears to their eyes, but the worst wasn't over. They were almost in a state of shock. With their eyes glazed and the circulation problems preventing any feeling in their lower extremities, the pain was not nearly a horrible state, I remember that never as bad as it would become. Later in the evening of their first day on land, Pradel was wheeled to a restaurant to have dinner with friends while Laurent slept in his hotel room. Pradel's meal consisted of two large steaks, a plate of vegetables, noodles and six large pieces of cake. Then he too retired for the evening.
    The next day, both men could barely move. Pradel, despite being given tranquilizers, was tortured by the dressings on his feet, which began to come back to life during the night. Tears welled in his eyes for three hours. Groggy, he kept asking for someone to help him. Finally, when he managed to fall asleep, he felt himself aboard the boat, unable to stop the rolling movement or the hammering of the waves in his ears. In his dream he stretched his hand for a tool and some food only to have the waves wash them away. With infected third degree burns over his feet and during the whole trip did he once complain."<<<<<


    It sounds as if they were in wose condition than Steven Callahan was after his seventy-six days in an inflatable liferaft between the Canaries and the Caribbean.


    Gernot H.

  13. #63
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    Default Re: A 20 foot cruising catamaran

    I would like to see someone do it in a wa'apa.
    “The difference between an adventurer and anybody else is that the youthful embrace of discovery, of self or of the world, is not muted by the responsibilities or the safety-catches of maturity.” Jonathan Borgais

  14. #64

    Default Re: A 20 foot cruising catamaran

    Hey Dan-- right now I'm shaping new rudders for the cartop cat, since my youngest son wants to borrow the boat for spring break-- he and some of his friends want to go down to Port St. Joe and camp.

    I sure hope this does the job. I'm thinking I'll just post plans on the web site for anyone who'd like to to try the basic design out-- I can't see charging anything for such a simple and modest boat.

    Anyway, here's the latest drawing for the 20 footer:



    Gernot, what an amazing story. Those two must be almost superhuman. I can't imagine what that must be like. Making the trip in a 20 footer with cabins would be incredibly luxurious in comparison. I think it is of cardinal importance to be able to stay dry and sheltered from the elements on any lengthy voyage.

    I guess, after reading that story, I have little excuse not to consider at least the possibility of such a crossing. My main concern would be that almost all the crossings in tiny cats have been east to west, the easier route from Europe to the Americas. I'd have to start out from the U.S. east coast, proceeding via Bermuda and the Azores. There is a strong probability of gales in the best season for that trip-- late May to early June.

    I hope that watermakers have improved. I've wondered if some simple water-driven pumping system could be contrived to work the watermaker-- it would slow the boat a little when in use, but you wouldn't have to use it constantly to get enough water for a couple of frugal people.
    Last edited by slidercat; 03-01-2011 at 04:05 PM.

  15. #65

    Default Re: A 20 foot cruising catamaran

    Well, as anyone who knows me might have guessed, the boat is almost nothing like it was a couple months back.

    I decided that I'd increase the length to 23 feet 8 inches. It may be that the Nacra 5.2 rig will not drive this larger boat to its maximum speed, but if not, I can always build a bigger rig, once I've seen whether or not the boat is a good one. I can also add a masthead forestay and upper shrouds, and fly a light air headsail to greatly increase sail area in light conditions.

    I've greatly simplified the accommodations, going for lightness, and maximizing the usability of the remaining amenities. No settee now, but two very comfortable single berths, a minimalist galley, plenty of accessible storage, and good sitting headroom over most of each berth. These changes allowed me to have very low houses, thus cutting down on windage.

    The biggest change, really, came about because I realized I was throwing away one of Slider's most lovable virtues-- her extremely comfortable seating. So now Slinger will have s small comfortable cockpit on each hull just at of the cabin, where the crew can be protected from the elements and yet be able to have good all-round vision. The crew won't have to worry about the boom while seated in the cockpits, and for a bad weather trip, dodgers could be added to give really good protection.

    Anyway, here's a profile:



    Another change is that I'm building her stitch and glue. The first hull is wired up, and I'm a little intimidated by her size:



    I had to lay a sort of scaffolding into the hull to get the second topside strake laced up. Luckily my balance is still good enough that i didn't fall out the side. I was quite surprised at how well all my edges matched up. The topside strakes are not quite developable, so there's a bit if convexity tortured into the hulls.



    I have to go out of town for a couple weeks, but when I get back, the hull ought to progress rapidly, with installation of bulkheads and stringers.

  16. #66
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    Default Re: A 20 foot cruising catamaran

    What other meaningful specs did you change (e.g. beam) and why did you change them, if so, when you seemed so set on the boat in its earlier form? Seating, alone, drove the boat to be this much bigger?
    It looks like the aft beam could be moved considerably aft from its indicated position in the drawings above, allowing for the desired seating within the original LOA, but the sheeting angle for the rig would change accordingly. Is the choice of rig the issue that shaped your decision? If it is, did you consider a different rig configuration?
    Last edited by Chris Ostlind; 07-01-2011 at 04:07 PM.

  17. #67
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    Default Re: A 20 foot cruising catamaran

    Having been on Jim Wharram's original Rongo as a kid on a shake-down cruise (felt like a real ship) and making acquaintance with a 20-footer last week:


    , which didn't even look too big in relation to my dinghy, I appreciate your wish for a few extra feet.
    How is the folding bridge arrangement coming on - patents applied for yet

    Gernot H.

  18. #68

    Default Re: A 20 foot cruising catamaran



    Of course, it's gone through dozens of changes. As I may have mentioned, my motto is to never make up my mind until I have no other choice.

    I had something happen to me that in retrospect is pretty funny. I had the first hull wired up, and as is my habit, I tabbed between the wires with little epoxy fillets. I removed the wires, and was starting to fillet and tape the hull at the bow, when I noticed I'd missed a couple of wires. As I started back toward the open transom to pull them, I heard a terrible ripping sound and I dropped about a foot. The only way out was the transom, so as I galloped aft, the hull opened up most of the way.

    More here:

    http://slidercat.com/blog/wordpress/?p=559

  19. #69
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    Default Re: A 20 foot cruising catamaran

    Here's my favourite Worry Cat , a 27 foot Tane Nui

    Try to work out what the marketing guy wants you to do then do precisely the opposite.

  20. #70

    Default Re: A 20 foot cruising catamaran

    We had a Tane for many years. Great boat.

  21. #71
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    Default Re: A 20 foot cruising catamaran

    There may be one in my future , very nice for the tropics and the islands .A bit minimal but that's good .
    Try to work out what the marketing guy wants you to do then do precisely the opposite.

  22. #72
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    Default Re: A 20 foot cruising catamaran

    Sorry to hear about your setback Ray, but I'm glad you got on with it! Keep cranking as much as the heat allows.

    Dan

  23. #73

    Default Re: A 20 foot cruising catamaran

    Hey Dan. I'm over it. I'm taking a short break from the big boat to build a yuloh for Slider. I've been threatening to do this for years, and I've finally decided to just do it. Even if I screw it up, I'll learn something.

  24. #74
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    Default Re: A 20 foot cruising catamaran

    Right on Ray

    Dan

  25. #75
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    Default Re: A 20 foot cruising catamaran

    Ray, great build, did you work on it today? I'm watching and learning.

    And, I always thought that wood boats were built by gluing up lumber higher and wider than the boat required, then cutting away everthing that was not the boat you wanted...

    Seriously, how time consuming and more difficult is it to form the sides as opposed to straight sides?

    And, is there no inside framing ?

  26. #76

    Default Re: A 20 foot cruising catamaran

    I try to work on it every day, if only a little, but yesterday was my wife's birthday. Also, I'm building a yuloh for my little 16 foot beachcruising cat, Slider.

    Yes, there is inside framing. The idea with stitch and glue is that unlike conventional ply on frame building, you build the boat from the outside in. The strakes are shaped in such a way that when wired together, they define the basic shape of the boat. It's pretty easy to arrive at these shapes if you have some sort of design software. I used Carlsson's Hulls. The software gives you the location of a number of points around the perimeter of the strakes. You join these points with a flexible batten, and then just cut the shapes out. I only had to measure one topside strake and then used that one to trace out the other three.

    The boat will also have a number of frames and bulkheads, as well as longitudinal stringers. These are cut out and tabbed into place, and then attached to the hull with epoxy and tape. There's always some debate as to which is the faster way to build, but Slider was conventional ply over frames and stringers, and I just wanted to try a good-sized build with stitch and glue.

  27. #77
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    Default Re: A 20 foot cruising catamaran

    Looks great to me! I just need to see more pics...

    And as to what you posted concerning the rounded hull and what Richard had to say; seemed he said the advantage of the rounded hull was surfing but there was the effects of yawing down a wave in heavy seas, that a chute may be necessary to deploy in heavy weather. I've looked at Slider and noticed that there didn't seem to be alot of rocker as with the dory hull. Have you motored Slider?

  28. #78
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    Default Re: A 20 foot cruising catamaran

    Ray can be more specific, but there's lots of rocker on Slider. That and the dory hull form is how he gets so much weight carry capacity on a 16' cat.

    Dan

  29. #79

    Default Re: A 20 foot cruising catamaran

    Dan's right. Slider does have a lot of rocker-- more than is considered optimal for a fast multi. But Slider has a very modest rig, and so great speed is not in the cards. My feeling was that the extra rocker would harm her speed potential less than a fatter hull would, and as it turned out, for her weight and sail area, she's pretty quick.

    No, I haven't motored Slider, but I would guess that she could be driven pretty well by a small outboard. Boats like Slider, with her slim 10 to 1 hulls, go through the hullspeed barrier without any fuss at all.

  30. #80
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    Default Re: A 20 foot cruising catamaran

    Thanks Ray and Dan. Ray, has anyone done Slider with a hard doger/cabin?

  31. #81
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    Default Re: A 20 foot cruising catamaran

    I see that would be the Slinger, I missed that. Ray, what about insulating your boats, I'v noticed few, if any, have insulated cabins/hulls. Going out on a 30 degree day can be nice, overnight stays are too cold for me, zero and a little wind makes it very cold. Seems heating an uninsulated cabin would get wet.

  32. #82

    Default Re: A 20 foot cruising catamaran

    Quote Originally Posted by Wavewacker View Post
    Thanks Ray and Dan. Ray, has anyone done Slider with a hard doger/cabin?




    This is the same Slider, built in Malta. The builder is an experimenter. He's got a big outboard on that boat too. I've thought about building a cover for the starboard cockpit, with a pipe berth, so sleeping in bad weather wouldn't require putting up a tent. This would only be feasible when I was sailing solo, of course.

    As to insulation, you could add that to any design, I would think. One nice thing about wood is that it does have some insulative qualities, so a wooden boat doesn't sweat as badly as a glass or metal boat if uninsulated.

  33. #83
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    Default Re: A 20 foot cruising catamaran

    I wouldn't get too excited about the R-Value of 1/4" plywood of any kind when it comes to boatbuilding. It rates at .31 R on the scale and is next to nothing, should one be considering the insulative scale. If you are looking for anything like the warmth potential of the average home, then a minimum 4" fiberglass batting insulative layer, as well as a vapor barrier beneath that insulation would be a reasonable starting point, with much higher R values being required for the real thing. Think about robbing your interior volume of 8"+ of space in total and you have a starting point. If you compress the insulation you add in order to get that all-too-valuable interior volume back again, you will be giving away the R-value as a trade-off.

    If cold water sailing is your game, then it's far better to go after a design that adresses this issue straight-up from the get-go, making use of more, or less, solid foam insulation and moving on from there. Yes, the boat will need to have increased interior volume in order to address this issue, so your garden variety multihull build is not going to get you there. Indicating solid foam for this application includes the use of a removable inner skin in the compartment and foam that is fitted, while not being permanently glued in place. Glued-in foam insulation has the potential to attract moisture between the foam and the wood strata which could lead to rot in wooden boats and it is not a good thing. Better to have it removable, as well as the covering layer, so that any possible maintenance issues can be addressed cleanly and quickly.

    You can always wear better insulating clothes in a layering strategy. There are some terrific mountaineering products available now that really slim-down that Michelin Man look, while giving extraordinary insulative qualities. I'll have a review of the gear that was shown at the recent Outdoor Retailer Show in Salt Lake City very soon on Duckworks and one of the newest product areas to be discussed will be insulation oriented layered wear that just might fit your interests.
    Last edited by Chris Ostlind; 08-19-2011 at 05:41 PM.

  34. #84
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    Default Re: A 20 foot cruising catamaran

    Thanks Ray, both look dryer. I wonder why the cabing top was not extended over the hulls for access? I'd like to stay with a 10 hp but no more than a 25 for economy, I'm in no hurry.

    Chris thanks as well, I was thinking of 1" of blue board and spray foam and in the design above, with the cabin, if the went from the outer edge of each hull I'd give up some interior volume. Insulating to the water line and below the sole might be easier. Does the vapor barier go toward the heated space as in home construction? 1" isn't much, but it's something and then if needed we could go with cold weather gear inside. My goal would not be an artic expedition but just braving cold nights at 15 or 20 degrees. A heater would be used and the cabin vented. I'm not trying to get this thread to my situation, sorry, for getting OT. Guess we could just say it would be for colder weather for the OP as well.

  35. #85

    Default Re: A 20 foot cruising catamaran

    Quote Originally Posted by Wavewacker View Post
    Thanks Ray, both look dryer. I wonder why the cabing top was not extended over the hulls for access? I'd like to stay with a 10 hp but no more than a 25 for economy, I'm in no hurry.
    I would guess because you need a good way to get forward. A cabin that extends from beam to beam puts a fair obstacle in your way.

    I think even a 10 horse outboard would be overkill. The builder of the first Malta Slider had his big outboard on the aft beam to begin with, and the boat was way out of trim. He had to move it forward. A 2.5 Suzuki would drive the boat at 5 or 6 knots I think, be very economical, and not weigh much either, a very important consideration for a cat.

    I think with these tiny boats, insulation is less practical than a down bag, which will keep you warm without the bulk of insulation.

  36. #86

    Default Re: A 20 foot cruising catamaran

    Once again I've changed my mind completely about the new boat's interior. Here's a drawing, showing that I now have the cabins extending aft much further, instead of the footwells/cockpits that I had in the last iteration of the design.



    I finally decided that I'd rather have the interior volume than the ultra-comfortable helmsman seating that was so successful with Slider. Now I just have to figure out an acceptably comfortable helm position. The cabin tops are only 17 inches above the center decks, so are at a good height for seating. Another issue is that instead of companionway hatches on the aft bulkhead, my main hatches will open onto the center deck, which is not quite as dry as aft-facing hatches. But all things considered, I think the added interior volume will be more useful in a boat intended for fairly extensive cruises.

    More details here.

  37. #87
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    Default Re: A 20 foot cruising catamaran

    keep at it Ray. Is the beam folding system still the same despite the other changes?

  38. #88

    Default Re: A 20 foot cruising catamaran

    Quote Originally Posted by skaraborgcraft View Post
    keep at it Ray. Is the beam folding system still the same despite the other changes?
    Well, sort of. The original idea was a system that folds at armpits and along the central spine, with a complicated arrangement of overlapping beam segments. But eventually I realized that a simpler and stronger approach would be to divide the functions of folding and beam connection-- an idea I got from Thomas Firth Jones' Brine Shrimp, which folds up along a central longitudinal seam, and uses bolt-on butt blocks to stabilize the hinges, which therefore don't have to carry any of the sailing loads. Now, my system is different, because I wanted something that could fold without needing to take down the mast, so the boat could be parked in a narrow slip, but the idea of separating the functions is what put me on the path to my present system-- that and a sliding beam system devised by one of my Slider builders in Italy. His system is not suitable for the new boat, because it doesn't have enough travel for a larger boat (though it will give his Slider a 10 foot beam) but it did make me notice that a U-shaped beam that slipped over my folding mechanism, and bolted to the beam webs on the hulls would achieve what I wanted. The major drawback is that the beams, being full width, will be somewhat awkward to handle when the boat is folded, and will have to be laid lengthwise between hulls and central spine. But the beams will be stronger than the original idea, and that's what is most important, as this boat will be taken offshore.

  39. #89
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    Default Re: A 20 foot cruising catamaran

    Cheers for the reply Ray. I just looked at Dudly Dix and he designed a folding tri way back,and it appears only one has been built,by a Russian. The system,though very versatile,looks complicated,if strong. I would possibly consider a folding multihull myself if i could find one that folds to less than 8ft, and does not take several hours to assemble afloat........and does not cost two arms and half a leg.

  40. #90

    Default Re: A 20 foot cruising catamaran

    Yes, there are lots of folding trimarans that work well-- half the cruising multihulls I see here are Farrier folders. It's harder to fold a cat. Lots of ingenuity has been put into the problem. I like Richard Woods' pod cats a lot. But my situation is that i have a 10 foot wide slip available for my use, due to the kindness of a neighbor, so my scheme has to fold without disturbing the mast, and without rotating the hulls.

  41. #91
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    Default Re: A 20 foot cruising catamaran

    i look forward to seeing the final solution to that dilemma. I recall seeing the Woods Wizard 22 in Plymouth some years ago, funky litle boat, it got me looking at multihulls in a different way. Still never owned one though, my current berth is 8ft wide, which is the limiting factor.

  42. #92
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    Default Re: A 20 foot cruising catamaran

    I like the change Ray! If it gets wet at the hatch you can always drop a curtain or close the hatch. Sitting on the top gives alot of seating.

    To push those hulls in and out,couldn't you use a screw jack incorporated in the beams?

  43. #93

    Default Re: A 20 foot cruising catamaran

    It's an interesting idea, and could be made to work, but my budget is primarily low-tech by necessity. I think, however, that if you were able to mold carbon beams and could afford extensive machine shop work for cutting big SS threaded rod, you could extend the beam by pushing a button. The problem for me, other than cost, is that I want my mast to remain up when the boat is folded. So the cabins swinging in and back relative to the central spine on which the mast and forestay are mounted allows the shrouds to remain more or less tensioned when the boat is folded.

  44. #94
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    Default Re: A 20 foot cruising catamaran

    Quote Originally Posted by slidercat View Post
    Once again I've changed my mind completely about the new boat's interior. Here's a drawing, showing that I now have the cabins extending aft much further, instead of the footwells/cockpits that I had in the last iteration of the design.



    I finally decided that I'd rather have the interior volume than the ultra-comfortable helmsman seating that was so successful with Slider. Now I just have to figure out an acceptably comfortable helm position. The cabin tops are only 17 inches above the center decks, so are at a good height for seating. Another issue is that instead of companionway hatches on the aft bulkhead, my main hatches will open onto the center deck, which is not quite as dry as aft-facing hatches. But all things considered, I think the added interior volume will be more useful in a boat intended for fairly extensive cruises.

    More details here.
    With two more steps, you can still have top mounted hatches--more of a ladder really. Additionally, you might be able to have some comfy seating on the deck if it's beefed up a bit. The deck could have a swiveling fishing chair mounted low.

    Did you get your details right on the folding mechanism?

    I was just thinking of another hybrid folding system. A Woods style pod salon coupled with the new seaclipper 20 style folding would keep it both upright rather than folded 90 degrees and narrow in the slip. The new Gougeon boat uses a similar folding setup.

    It isn't practical for your setup, but might work.

    Dan

  45. #95
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    Default Re: A 20 foot cruising catamaran

    Sliding beams are just one strategy when it comes to compressing cats, be they sport, or cruising applications, for trailer legal beam. Some time back, I drew-up a sliding beam cat by the name of Neo 21 http://www.lunadadesign.com/neo-21-s...catamaran.html , with technology openly borrowed from Mike Leneman's L7 trimaran http://home.comcast.net/~ritakend/site/ The boat was originally designed for Dan St.Gean to a fairly flexible use parameter. Dan chose to go with another deisgn that, as he suggested, allowed him to build the boat more quickly within the space he had available and within the time frame he had to complete the project. Several sets of plans for the boat have been sold, but to this date, it has not been built.

    Still, the business of sliding beams across the gap betwen the hulls of a cat is not a new thing. There are all sorts of design motifs one could adapt to the established technology. The single limitation for the build and use of such a cat is in the eventual max beam that is available as a final sailing boat.

    After this technology (sliding beams), one needs to go into all sorts of other, more complex adaptations that could involve the radius sweeping of the beams to allow the boat to fold, the lifting and removal of the central pod to allow the beams to compress in one of several different manners for trailering with the pod dropped back in place on the trailer, the actual folding of the beams to a flat position... and on and on it goes with a collection of jigger this, and fiddle that, build a trick trailer this and mess with that, until one simply finds themselves bewildered by the array of solutions available.

    The way I see it, there's a built-in limiting factor for the business and it resides somewhere in the 20-22 foot region for LOA. After that, you are off into a realm of various design constraints and physical limitations that may, or may not meet your needs, and/or personal manual capabilities. Of all the folding strategies that are out there, I think that the one presented by the Cat2fold system is the most elegant. Yes, it can cost you in terms of structural build elements that allow it to happen, but it makes for the simplest method to launch and then retrieve the boat. The original Cat2fold http://www.cat2fold.com/ was built to a 36" LOA requirement and the first version, which was fabricated in New Zealand and then shipped to SoCal for final fitting out, performed beautifully under sail, as well as a trailered craft that could be launched at many different locations. Smaller versions of the Cat2fold system have been kicked around, but to date, none have been built. Kurt Hughes has a better take on all this, as he did the original engineered design solutions from Rafi's concept work.

    The patented folding mechanism design is still out there and available for someone who may enjoy this style of catamaran while still retaining folding capabilities in order to trailer the boat to a chosen sailing ground. If you are interested, please give a shout to Kurt Hughes and I'm sure that he can put you in touch with the designer, or his agent. http://www.multihulldesigns.com/

  46. #96

    Default Re: A 20 foot cruising catamaran

    Quote Originally Posted by Dan St Gean View Post
    With two more steps, you can still have top mounted hatches--more of a ladder really. Additionally, you might be able to have some comfy seating on the deck if it's beefed up a bit. The deck could have a swiveling fishing chair mounted low.

    Did you get your details right on the folding mechanism?

    I was just thinking of another hybrid folding system. A Woods style pod salon coupled with the new seaclipper 20 style folding would keep it both upright rather than folded 90 degrees and narrow in the slip. The new Gougeon boat uses a similar folding setup.

    It isn't practical for your setup, but might work.

    Dan
    Dan, I think you're advocating a manhole cover, which has to be the most miserable way to get into a cabin ever devised. I once went aboard a MacGregor 36 with the setup, and it was awful. Once you'd wriggled down inside, it was like home for a skinny vampire, and just as dark and confining. I have to have washboards-- I'm old and feeble.

    I hate to tell you this, but I'm about to rock your world. Recently one of my builders in Italy sent me pics of his system for extending his Slider's beam, and it would work like a charm for your Tamanu. See this blog post: You could very easily have 10 feet of beam in exchange for a couple minutes of wrench twirling.

    I've also got pictures there of a model I made to determine the feasibility of my folding system.

  47. #97
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    Aug 2011
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    St. Petersburg, FL
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    14

    Default Re: A 20 foot cruising catamaran

    (Bearing in mind I am new, never built a boat and am no engineer...)

    How barbaric would it be to have removable supports instead of the long, straight sections moving forward over the deckspace like that? I am picturing those straight sections as removable C-channel beams that slip over the folded beams and bolted once the hulls are spread. I don't know how sturdy or by what method you intend to make the hinges, but it doesn't seem like they'd be any different than the model, if those long support beans were just lifted off the foldy part before you folded them up. (And yes, I read that you may already be onto that, of course )
    -James

  48. #98

    Default Re: A 20 foot cruising catamaran

    Quote Originally Posted by NomadRip View Post
    (Bearing in mind I am new, never built a boat and am no engineer...)

    How barbaric would it be to have removable supports instead of the long, straight sections moving forward over the deckspace like that? I am picturing those straight sections as removable C-channel beams that slip over the folded beams and bolted once the hulls are spread. I don't know how sturdy or by what method you intend to make the hinges, but it doesn't seem like they'd be any different than the model, if those long support beans were just lifted off the foldy part before you folded them up. (And yes, I read that you may already be onto that, of course )
    Are you sure you aren't an engineer? That was a really good guess. That's pretty much exactly what I plan to try. The structural channel beams will resist the forces trying to pry them apart at the bottom because they are bolted to the beam webs (the parts attached to the hulls.) They'll also have a big bolt in the center to attach them to the central spine in an unambiguous way. Because the hinges will tend to sag under the compression forces of the rig, I'll use a ratcheting strap at each central spine connector to pull the spine up tight into the channel beams so they can be pinned in place. There will be 10 bolts in all, a lot, but I can spin a wrench pretty fast, and I bet I can snug them all down in less than five minutes.

    The great advantage of this approach over some others I considered is that I can have as much beam as I want. Another is that there is no friction to overcome, as there is with sliding beam systems. The boat can be unfolded by pulling on a line-- no winch needed.

    As I explained in the blog piece, the whole idea was to separate the function of folding and the structural requirements of the beams. I once saw pictures of a cat that had been designed to fold in a similar manner, at the armpits and a central spine, but instead of separating the functions, the designer went for massive aluminum weldments, so that the folding mechanism would be strong enough to take the sailing forces. I think only a couple were built, and they must have been pretty heavy and expensive.

  49. #99
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    Nov 2004
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    Default Re: A 20 foot cruising catamaran

    Replies within.
    Quote Originally Posted by slidercat View Post
    Dan, I think you're advocating a manhole cover, which has to be the most miserable way to get into a cabin ever devised. I once went aboard a MacGregor 36 with the setup, and it was awful. Once you'd wriggled down inside, it was like home for a skinny vampire, and just as dark and confining. I have to have washboards-- I'm old and feeble.

    The hulls would be like Richard Woods' hulls on his Wizard--largely for storage while the central section would be the salon.

    I hate to tell you this, but I'm about to rock your world. Recently one of my builders in Italy sent me pics of his system for extending his Slider's beam, and it would work like a charm for your Tamanu. See this blog post: You could very easily have 10 feet of beam in exchange for a couple minutes of wrench twirling.

    Good idea. I'm going to mess with my current setup at 8'6 for a while though. The allure of a boat that can be launched quickly AND have additional sailing beam is alluring. Like Chris said though, I didn't have the time to incorporate the Neo's design ideas (or build it) in time for the T200. Additionally, I was splitting the labor with my sailing buddy Brian. Our initial thought was to use the hulls once for cat use and then have an outrigger each. It was so nice as a cat we decided to go with that approach. One nice thing about the H18 rig we were using is it had a roller furling jib. Nice for sail reduction & later after cracking the luff groove of the main beam, we were able to limp on all points of sail with just the jib--with a new leeboard location all the way forward. Essentially, I'm looking for a high volume load carrying H21SC & am pretty close. I'll probably use your wood slat deck idea for this boat.

    I've also got pictures there of a model I made to determine the feasibility of my folding system.

    With sailing beams of sufficient width, I don't see why you can't have whatever beam suits you best. Handling and storing them will be a bigger problem as they get longer though.

  50. #100

    Default Re: A 20 foot cruising catamaran

    Quote Originally Posted by Dan St Gean View Post
    Good idea. I'm going to mess with my current setup at 8'6 for a while though. The allure of a boat that can be launched quickly AND have additional sailing beam is alluring.
    The wonderful thing about Renato's idea is that it solves the friction problem that affects just about every sliding beam system I've ever seen. The only friction involved is the friction of the bolts sliding in the slots-- everything thing else can have loose tolerances. Face the slot with graphite, or better yet, ultra high density plastic, and you'd have a system that would open and close effortlessly. If I weren't deep into the new boat, I think I'd build a 19 foot version of Slider, using that system, and put a beach cat rig on it. Then I'd have comfort and speed.

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