Proa design

Discussion in 'Multihulls' started by Tcubed, Sep 13, 2008.

  1. RHough
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    RHough Retro Dude

    How would this rig allow a proa to sail in both directions?
     
  2. rwatson
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    rwatson Senior Member

    Yes, especially with the hull not being symetric fore and aft in the XLS diagram - are you sure you are "up to speed" with the Proa concept Mainstay?

    You gotta be able to sail backwards and forwards.

    Rob has a couple of shunting videos on his site for clarification if you want to check it out ( links just a few Posts ago)

    re the balestrom,unstayed mast option - I guess a comparison of costs would be in order here. It might be worth a less handy rig if there were substantial cost saving to be made. I know the average carbon fibre mast isnt cheap.

    Any sample costs available Rob?
     
  3. rob denney
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    rob denney Senior Member

    G'day,

    Tcubed
    Immerse the flare, the boat slows down. Immerse the long skinny tube, nothing noticable happens. Hence my comment that flare is drag.

    You are quite correct, it is neither appropriate nor fair to contemplate extending the length of a lee hull which is "high enough to keep the ends out of the water, no matter what", strong enough to take the forestay loads and wide enough to stand on. If, on the other (harry) hand, a 10% length increase adds less than 5% to the cost and weight of the hull it makes perfect sense to make it as long as possible.

    Extending the shed, or building the small lee hull in pieces is no big deal (my 50 footer has 5' removable at each end for easy containerisation), nor is maneuvering with two harry size rudders. Extra sail is not a requirement, just be content with the higher speed, nicer motion and increased safety.

    It seems you are justifying your design based on what it is rather than what it could be. The same could be said about the location of your accommodation and rig type.

    There is no evidence or reason that I know of that a hogged sheer causes nosediving or broaching. Harry's track as if they are on rails, and need to be driven very hard to immerse the bows, and even then, they are in no danger of pitchpoling until the bows are very immersed.

    The slight variations in immersion and wetted surface caused by U, semi circular or parabolic hull sectional shape are secondary concerns if your hull is twice as heavy as it could be.

    "Quite difficult to trip" is nowhere near safe enough, at least for me. If you can avoid beam seas under bare poles for a couple of days in a storm, you are doing well. And the max righting moment is still less than having the accommodation in the ww hull, so it is a pretty nebulous safety feature. Add in the drag from waves hitting it and it is slow as well.

    The relevant windage is at 30 degrees off the windward bow, which is where the wind blows from while sailing to windward. The harry with a similar comfort level as your boat has 18.5 sq m of area including rigging, beam mounted rudders and both beams. All are aerodynamic shapes.

    If we include your "lee bows high enough not to submerge", standing rigging (over 1 sq m of very unaerodynamic shape) and full length windward hull with enough freeboard for it to support the entire boat when caught aback then my bet is the harry will have less.

    Happy to compete in a race, yunder whatever terms you want. The harry with the same fit out level and payload as your boat will have a comfortable covered cockpit, easy access to the rig and deck, and be dry to sail. Based on Russ' boats and the harrys sailing, it will be about 50% lighter and cheaper in sailing configuration. These attributes are directly attributable to it being a harry configuration and not a Russ one. Look forward to seeing detailed plans and weight analysis of your boat.

    Mainstay,
    I cannot open your rig drawing, but any design with as many parts to fail as a stayed mast has, has no place on a sensible cruising boat.

    Rwatson,
    The mast on the boat in the video (http://www.youtube.com/watch?v=8chR6DAFjGA) was the first one we built and there was a fair bit of stuffing around involved. It cost $12,000 and is for a righting moment of 18 tonne/metres. Painting and the lightweight carbon track added another couple of grand. The boom is an open topped design which was more complex than it needed to be, a box boom would cost about $8,000. Fittings for the jib and the bearings for the mast maybe another $2,000, depending on what was required. Say $Aus25,000 all up, to build it in Australia where the charge out rate was $65/hour. 75% of the cost is labour. In Panama, where we might be building masts next year, it is about $20/hour and in China, where we might be building masts later this year, it is about $5 per hour. If I was to do it again, I would make it a wing mast, with in boom roller reefing. Cost would be a little more, efficiency a lot more.

    This is not a "less handy rig". This is a very simple rig with almost nothing to go wrong, replace or maintain. It can be easily handled by one person with very little effort. It is also highly efficient, about the same as a conventional rig upwind and superior reaching and running according to tests done by the Woolfson unit.

    regards,

    Rob
     
  4. Tcubed
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    Tcubed Boat Designer

    Although i'm always interested in new rig ideas, attaching sails to stays instead of spars makes for poor engineering, because of the colossal tension required to keep the stay straight(ish), which implies more compression stress, meaning a more robust and heavier mast. This is the downside of any jib and why i favor small jibs/large mains-and this is a more aerodynamically efficient solution as well. Unfortunately, single masted proas must have the mast in the middle of the boat (unless movable mast step, which i don't think anyone will say is practical for this size!) so the jib ends up somewhat larger than what i would consider ideal.

    The compression force on the mast of a sloop rigged proa as drawn above is

    C = Wa + 2(T*I)/(sqrt(I^2+J^2))

    where C is the compression on the mast, Wa is the weight of the windward hull, T is the tension in the forestay, I is the height of the foretriangle, and J is the base of the foretriangle. I made a couple of simplifications for this formula but that's the bulk of it.

    I tried to figure forestay tension based on aerodynamic force of jib and % sag in the stay but did not get very far.
    Q*If someone has the formula for this i would very much appreciate it.

    In the balestrone rig there is compression too but only due to jib, which is also quite small, and this compression is not transmitted to the mast step, but rather to the gooseneck.

    As for roller reefing, i wouldn't consider it. Period.
    These are the reasons:
    1*They are complex pieces of equipment that i have personally seen break, jam or otherwwise malfunction too many times to count. (I do rigging work)
    2*They create a ton of windage when fully furled-comparable to having another mast.
    3*They don't actually save much effort. To reduce sail you have to WINCH in the drum rope..On a normal jib you just let the halyard go, and if the wind is blowing it partly back up the stay, you can yank on a downhaul (if you've decided to have one). It's true to raise a jib is more work than letting out a roller furler, but what's important is how quickly can you dump sail, not how quickly can you set it. Seaworthiness is important.
    4*I have yet to see a roller furling sail that has a nice shape when reefed.
    5*There always exists a wind strength which will break open the wraps-just look at what happens to people's roller furling jibs after a hurricane, if they neglect to remove the sail completely beforehand.
    6*To remove the sail completely, it must first be completely unfurled. By the time it's blowing so hard you decide it might have been better to bring it in completely, you cannot unfurl it anymore!
    7*They are expensive.

    To give one juicy example of point #1 i'll relate how a modern french schooner with all roller furling sails got caught in ever increasing winds. They got a jam in the foresail and tried everything they could to free it, but couldn't, leaving that sail permanently one third reefed. Meanwhile, they reduced the other sails appropriately. Eventually it was blowing so hard the foresail burst into horizontal banners, which after a while of thunderous shaking, brought down the foremast. To make things worse yet, the foremast wildly swinging around on the end of the triatic eventually brought down the mainmast too...From one little glitch to complete de-rigging.
    Sails must come down with 100% reliability-not 99.999%

    I have the mast deck stepped as it's a fully rotating wing mast. It is stepped on the windward side of the leeward hull with some clever WEST system laminates underneath to spread out the load using a minimum of material and taking up little space inside. The mast is strip planked spruce built up on 6 mM plywood forms every meter or so all epoxied together. No glass anywhere, i feel it adds more weight than strength. A glass sheath also has different modulus of elasticity to wood and can, through stress, develop invisible cracks which let water in and rots the mast. Water does not rot wood, trapped water rots it. Chord is about 65 cM , thickness about 20 cM. One set of very light diamonds keep it rigid across the thin axis. An extremely rigid setup- so wall thickness can be quite small. Just how small i don't know yet.
    Q*Maybe someone can relate some examples of wall thicknesses in comparable wooden masts.?

    BTW adaptation is quite possible as so far it is only on paper. I hope to be able to start building within a couple of years.
     
  5. Tcubed
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    Tcubed Boat Designer

    <<<<<It seems you are justifying your design based on what it is rather than what it could be. The same could be said about the location of your accommodation and rig type.>>>>>

    Good point.
     
  6. Tcubed
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    Tcubed Boat Designer

    <<<You are quite correct, it is neither appropriate nor fair to contemplate extending the length of a lee hull which is "high enough to keep the ends out of the water, no matter what", strong enough to take the forestay loads and wide enough to stand on. If, on the other (harry) hand, a 10% length increase adds less than 5% to the cost and weight of the hull it makes perfect sense to make it as long as possible.>>>>

    Ok, but suppose you ARE length constrained.
     
  7. RHough
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    RHough Retro Dude

    Don't worry too much. The last we heard, a Hobie was being coverted to the "Mainstay (tm)" rig as a proof of concept. That was in March of this year. No word since. As you point out, the idea of setting sails on stays is not ideal, this rig uses a shroud rather than a fore and aft stay. What tension there is in the "main luff" wire will be different on each tack on a conventional boat. On a pacific proa, the "main luff" wire will always be the leeward shroud and have the least tension of any wire in the rig. If the rig was put on an atlantic proa, at least the "main luff" wire would be the higher tensioned shroud. ;)
     
  8. rob denney
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    rob denney Senior Member

    Ok, but suppose you ARE length constrained.[/QUOTE]

    Story of my life! ;-)

    My design spiral starts with the expected payload of the boat, including accommodation. I then design a windward hull around this. Next is the Bruce number and /or the required wind to lift a hull. This then goes on the longest, lowest, narrowest lee hull possible, within engineering restrictions. For cruisers I work on the lee bow being 50% immersed with the ww hull flying, so I guess the answer to your question is I would make the bows higher, although not wider. However, I would keep the same section shape.

    The boat in the video was much heavier than the original design as the owner decided he wanted a bunch of add ons after the lee hull was built. This has lead to it being, effectively, length limited. It still performs well, and if you can get your boat down to this weight, then I see no reason for high flared bows, except to give you somewhere to change the jib, if you choose this rig option. As I said, mixing Russ and harry is fraught, so changing the bow leads to changing the rig, which leads to eliminating the pod (big hole in highly stressed area, plus internal space limits), which leads to moving everything to the windward hull and allows you to build a much smaller lee hull. But not doing all of these will lead to problems.

    I should also admit that to make them easier to build from flat panels, I am now putting flat decks on my boats. However, the decks at the bows are very narrow, so I do not expect there to be any nose diving ramifications.

    All going well, there will be a stripped out 15m/50' harry in Panama early next year. I would be happy to take you for a sail if you can get there.

    I completely agree with you about roller reefing headsails. A heavy waste of money. However, I would not be that happy about a lowered jib sitting on the aft deck, and even less happy about having to unhank it and rehank it on the other end every shunt.

    I completely disagree with you about no glass on strip planked wooden masts. It may not rot but there are twisting loads, Euler buckling and "bursting" of lengthwise fibres under compression to consider. You must restrain the fibres with some off axis material and glass is good for this. The different moduli are not a problem as the wood is lengthwise and the glass is at +/-45. A wing mast with a gunter will be an interesting beast, particularly when reefed.

    Wood is a great building material, but is heavy compared to carbon, and for a wing mast, foam. An 18m/60' length of your mast will weigh about 90 kgs/200 lbs, without any off axis material (minimum 25 kgs if you use 6 ounce/200 gsm inside and out), fittings (track, hounds, head, ball joint, gooseneck, wires and spreaders) or local beefing up at the hounds, diamonds, top and bottom (probably near enough solid at each of these). I would be surprised if it ended up any lighter than 150 kgs, compared to 120 kgs for the unstayed carbon/glass mast in the video. I would be further surprised if 6mm spruce is sufficient to take the loads from the tight staying angle if the rig is caught aback.

    With the price of mast quality spruce in most of the world, it will also be more expensive than a carbon mast.

    regards,

    Rob
     
  9. boat fan
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    boat fan Senior Member

    Hello Rob ,

    Question : Is it at all possible to build a Harryproa (for example a Visionarry Sport) out of plywood, maybe Hoop Pine /stringers on frame , or would it just be too heavy ?
     
  10. rob denney
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    rob denney Senior Member

    G'day,

    Certainly could, although it would take longer and may not be much cheaper. The added weight would need to be trimmed from the payload, or you accept a heavier/slower boat. Maybe make it a little longer to compensate. The Vis is 12mm kiri with 600 gsm glass each side. Similar stiffness and puncture resistance (strength is not an issue) would use 12mm ply with 200 glass on the outside, 3 coats of epoxy on the inside. The kiri weighs 5.9 kgs, the hoop about 8.5 kgs. Surface area is 200 sq m, so you are adding half a ton. I am not sure of the price difference. You could use thinner hoop and put in more frames and stringers, but I doubt the savings would be huge.

    You are also shape constrained, but not enough to worry about.

    The quickest build is undoubtedly to use partially glassed flat panels for everything. Depending on resin and core selection, this is also the cheapest, I think.

    Any questions, let me know.

    regards,

    Rob
     
  11. boat fan
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    boat fan Senior Member

    Thank you Rob , great reply.

    I like plywood I`m afraid.I know how to use it and therefore I am confident to build that way.

    As to weight , I do believe it could be done in 9 mm ply .I looked at the Peter Snell Easy 37.Similar accommodations to a Harryproa. Those boats are light .

    I enquired about the Easy payloads and Anne Snell was kind enough to reply with the following :


    http://easycatamarans.com.au/

    It made me think that the Harryproa could be built to similar specs (scantlings ) .

    I think a very attractive boat could be built in multi chine.
     
  12. rob denney
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    rob denney Senior Member

    G'day,

    A nice reply from Anne. They are more in tune with low cost building than most of the other main stream aussie designers. 2,500 kgs/2.5 tons is pretty good for a 10.5m/35' cat shell, but it compares with 2,000/2 tons for a 15m/50' Visionarry or under 1,000 kgs/1 ton for a 12m/40' harry, both ready to sail.

    Still, no reason why you couldn't build in ply if that is what you are comfortable with. 9mm would probably need a bit more framework on the lee hull of the visionarry, but harry is 8mm kiri so 9mm would be ample. It would be easy enough to build a rockerless hull from ply and compared to strip planking, panel boats or foam one offs, it would be pretty quick. Could also build it from tortured ply, or as I did with the first harry, bending ply. Been a while since I have drawn anything in ply, but it would be fun seeing what can be done.

    regards,

    Rob
     
  13. Tcubed
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    Tcubed Boat Designer

    masts and general construction

    Interesting to see your design process and approach, Rob. I think we're pretty much agreed on most points, and on the points that we're not, we're pretty much agreed that we are disagreed. Thank Jah it is like this, otherwise there would only be one designer in the world and all boats would look identical!!

    Re the mast. I'm getting basic figures for the 14.3 M mast of 45 kg for all the wood + ~25 kg for all the hardware (track, three blocks, the little diamond spreaders and some straps) + ~1 kg = 75 kg , say. All the standing rigging comes out at ~30.5 kg. And let's not leave out the sprit at around 18 kg for a grand total of 123.5 kg approx...

    Now that is with no glass, and yes you're right about the glass not cracking if it's not in line. However, I still prefer all wood. I can substitute the glass fibers for lightweight woodfibers at +/- 30 degrees in a layer of veneer cold molded over the strip planks to achieve the same thing and spare myself the hassle of making the mast in two halves to subsequently join. But each to his favorite method i guess.
    However your cost comment on carbon fiber is really surprising. I don't know about Aus. prices, but here wood is still cheaper than carbon fiber, even sitka spruce.

    I, like you B. fan, am very enthusiastic about plywood construction, and in fact, had originally designed this boat to be made out of 6 mM marine ply with a fairly extensive array of edge set stringers and frames skeleton, with a five panel shape. One day, i met a fellow called John Patterson on a very professionally self built trimaran. He had used strip planking, with a unidirectional glass layer oriented athwartships inside and out. The result was strong, light, no shape limitations, completely frameless interior, but what really impressed me was how fast it was to build. The more i thought about it the more convinced i became, so i will basically use his method to create the hulls. Scroll near the bottom of:
    http://www.nemasail.org/pdf/Spring2005.pdf
    to read more about this great home made tri.

    But, don't think i'm saying don't build it in ply, quite the contrary. I would say, however that with 12 mM ply and at least five panels to make up a hull (so the flats are not too wide) you would barely need any frames if the shape is nice to cut, and not slam and for these kinds of ultra low displacements. 9 mM is better, but with more skeleton (more work but better strength/materials ratio). Scantlings are decided by boat weight more than anything else. I was designing for 6 mM ply but then the skeleton becomes quite complex. I sailed on a 42 foot newick style tri and it was 6 mM ply and i could not detect any flexing. The skeleton wasn't even all that elaborate either. He did have a layer of glass on the outside.

    Q*Another topic for discussion is pros and cons of rocker. Rocker allows to design for emmersed length in light conditions and full length in heavier winds, allows for improved maneuverability, but it is difficult to get high prismatic into it and some opine that it leads to strange or excessive pitching . I wonder though whether prismatic doesn't sometimes get confused with longitudinal distribution of reserve buoyancy...and why would a blunter curve of areas be less drag at higher froude numbers anyways? If i remember right, Uffa Fox had this full prismatic coefficient analysis in one of his famous books. Anyone care to give us a refresher?
     
  14. boat fan
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    boat fan Senior Member

    Thank you once again Rob , another great reply.

    Anne was nice , and helpful.

    I don`t know much about bending ply . I always have this fear of tortured plywood not turning out the same as the planned sectional shape.I did build a mosquito cat many years ago , which turned out pretty ok , so I`m probably just paranoid :D I have " Gougeon Brothers On Boat Construction and their experiments and results freaked me a little - seems a little " hit and miss" - :D

    I`m more concerned about the mast step / bearing / bulkhead structure.
    I have tried to find some photos of your boats showing what is involved with all that , but could not find much.Are we talking something like two strong bulheads at the mast step / bearings , or is there more structure ?I suppose it would end up the same as the stripped Kiri boats.Just worried about the weights of all that....Given that you don`t need the big truss type cross beam needed to carry the rig on a cat , you may well come out even there....Just pondering...I think I will will build a model in flat panel , make it look " pretty " as I can ;)

    http://lh5.ggpht.com/terhohalme/SMLo5OgCbYI/AAAAAAAAANc/jH2osSyhcU4/catharsis 27 persp5.jpg

    A double ended version of Terhalme`s Catharsis 27 or similar ?

    As for the full size boat , I think it could be a quick build.
     

  15. boat fan
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    boat fan Senior Member

    http://lh5.ggpht.com/terhohalme/SMLo5OgCbYI/AAAAAAAAANc/jH2osSyhcU4/s640/catharsis 27 persp5.jpg
    http://lh5.ggpht.com/terhohalme/SMQHBSzXWpI/AAAAAAAAAPg/shzs18EZ1_Q/s512/IMG_1070.JPG
    http://lh3.ggpht.com/terhohalme/SMQGi63L70I/AAAAAAAAAPU/dMjL-a57HKs/s512/IMG_1072.JPG


    I think 12 mm is too heavy.If I were to do this in ply , I think 9 mm is the way forward. I dont think the lw hull on Rob`s boat would take long to build that way.I would run a couple of 19 x 42 mm stringers along the side ( widest ) panels to stiffen them up a little.I think the mast bulkheads / bearing framing would have the most structure in the long hull.Given that the interior of that hull would not require much more than 2 or 3 coats of epoxy , there is fairing on the external chines then glass then paint .

    The windward hull would require little in the way of framing on Rob`s boat I think.Rob`s galley stretches the best part of the outer windward hull face. Lots of additional stiffness there ! So...I would attempt mainly stitch and glue with filleted bulkheads I think.Those pics above are by terhohalme and his Catharsis 27.He used nidaplast , but also designed for 9 mm ply.Build would be very near the same he says.I see Rob`s windward hull looking similar to this boat , double ended of course.
     
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