Shunting Catamaran?

Discussion in 'Multihulls' started by member 76956, May 15, 2022.

  1. member 76956

    member 76956 Previous Member

    For about the last week, I've been thinking about all the innovations that were made with the Harrys, like the simple to contruct rockerless hulls, the stayless rigging and the safety and error resistant maneuvering. It seems natural to me that these benefits could be applied to a cat.

    Why not a shunting cat?

    *There may be very good reasons why not; but, I still like the idea for now.

    I recently watched a video on a biplane rigged cat called Oryx. I liked it right away. I haven't gotten to the driving proceedure yet; but, I hope to learn more soon. I think I'm also starting to develop design priorities. I like the approach of designing around the bed; not just the sleeping bed, but the flat-bed as well, or rather load, both human and cargo, if any. So, I think I'm prioritizing load, live-ability and beach-ability. I also think I know how I'd modify a Harry, if I got one tomorrow. They would be extensive mods and it would definitely be slower.

    So, the picture I have in my mind's eye is a shunting cat, with rockerless hulls, a stayless biplane rig with balanced lugs. I'm also envisioning the biplane rig as a double-schooner, which may be complete fantasy; but, again, I like it for now.

    This is strictly whiteboard stuff. I'm just throwing it out there, hoping not to get pooped too badly.
  2. lucdekeyser
    Joined: Aug 2004
    Posts: 157
    Likes: 13, Points: 18, Legacy Rep: 51
    Location: Belgium

    lucdekeyser Senior Member

    Why call it a cat? Call it a proa with two identical hulls and rigs.
  3. member 76956

    member 76956 Previous Member

    Makes sense to me.

    How about "symmetrical" proa?

    Thanks for the reply.

    I know you guys are serious yachtsmen and I'm taking my chances with this one. I do think there's going to be something useful here eventually.

    BTW, I actually did think about using two lee hulls. At the plan level I'd probably widen them, just slightly, at the the above the waterline portion at least. I also think I'd significantly increase the freeboard, to increase the internal volume. The ancient ships of the line, had tons of it; and they had tons of internal volume. Of course, I just increased the cost of the build and either raised the height of the masts and the CE, changed the sail geometry and distance between masts, or all of the foregoing. Perhaps, just changing the sail geometry "slightly" and the distance between the masts can mitigate this, without significantly raising the CE?

    I think I should probably have more distance between the hulls now too, to maintain the righting moment. For now, I think the target should be to get the theoreticals moving back towards that of the Harrys, as a baseline, after the mods have been figured in.
    Last edited: May 15, 2022
  4. rob denney
    Joined: Feb 2005
    Posts: 871
    Likes: 258, Points: 63, Legacy Rep: 436
    Location: Australia

    rob denney Senior Member

    We have done a number of design studies for "Harrycats". The extra space is not easily usable, and if it was, it is weight in the wrong place (more pitching). It would also add drag to the windward hull, making steering harder (but not impossible) to balance and increase the load, and weight of the beams and rigs. The design spiral starts going the wrong way for no obvious gains.

    If you did proceed down this path, I would make the beam narrower, not wider. This pretty much replaces usable space (on the deck) for unsuable space in the ends of the ww hull.

    It would make tacking in some breeze a viable option, but no one who has shunted on a well set up proa thinks this is a benefit.

  5. member 76956

    member 76956 Previous Member

    Thanks again for the reply

    Are these studies you're referring to public or is this your proprietary work? In either case, I appreciate the input. I just want to get a better idea for where the obstacles are. This is both a learning exercise for me and a creative outlet. My first boat, ~ 12 months away, will likely be an off-the-rack, second-hand market sloop, just to get on the water.

    I'm not intending to canibalize an existing Harry for this, rather use one for inspiration, maybe.

    I also think I may not be describing this well. I'll eventually get better at it I think. I also don't think I'm understanding all of your comments, since I'm envisioning this as a biplane-rig, with identical hulls, which should be steering neutral. I'm mostly referring to the Opus here. In the OP, I "also" mentioned modding a Harry, if I were to obtain one. I probably shouldn't discuss both of these things in the same thread. I'm probably not making that clear. Writer's teething pains. I'll try to do better.

    With regards to modding a Harry, I'd approach modding an existing vessel differently than modding a set of plans. I really wasn't ready to talk about this yet; but, my gut reaction to the Harrys is mixed. It's a combination of "cool idea," with "I'd arrange the living space differently," maybe add more. I could change my mind after I see one up-close, which I hope I get to do.

    What I keep "wanting" to do with the C50s & C60s is add more enclosed living space. I like the galley, "up" where it is; but, I feel like there "could" be a combined "owners" stateroom-mini galley above it, directly under the stars. For the below deck cabins, I want to open those areas up to more & better views and more sunlight with large picture-frame windows. If this is a structural issue, there's a very strong transparent material called ALON (aluminum oxinitride), that I think would be suitable. This stuff is "da-bom," as they say on the US west-coast. You could make hulls from it, it's that strong. It's also probably very expensive. It's my understanding that there's transparent carbon-fibre too.

    Adding an extra level to the ww hull, may occult the lower portion of the sails, which may require altering the rig, by raising it and possibly the upper extreme of the lee hull and requiring taller masts, which could be mitigated by placing the masts farther apart and making the sails wider. This may now require climbing to physically handle the sails (my first yuk). I haven't thought of a way to mitigate that yet. Also, while at it, I would widen the "above-deck" portion of the lee hull, definitely making available more living, workshop, storage space, etc; but, necessitating lengthening the beams to maintain or increase usable deck space. It wouldn't be as aerodynamically clean; but, the hydrodynamics shouldn't be affected. This is plan level stuff only.

    For an existing vessel, the only apparent way, I can think of, to add more living or workshop space, etc; would be to add some kind of light-weight temporary container to the deck, with extra beds, second galley, wet-bar, machine tools, diving compressors, or whatever additional equipment is needed or wanted. This could be a very satisfactory solution. I just don't want to encroach on the tender's space. Otherwise, I will have to find some place to hang it. I'd add one or two small deck cranes too. On a personal level, I spent a few years working in a machine-shop and want a space for miniature machine-shop and electronics hobby tools. These can come very small, they just have to go "somewhere," definitely not the galley.
    Last edited: May 16, 2022
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.