Unstayed carbon fiber mast on cruising catamaran?

Discussion in 'Multihulls' started by Nico Crispi, Jul 15, 2017.

  1. catsketcher
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    catsketcher Senior Member

    Groper, I haven't sailed one of these rigs but the magic 90 degrees is the apparent wind angle not the true angle. If I get the reacher up on Kankama in 7 knots breeze and get the boat wound up I can bear off as the apparent comes forward. In the end I can be doing about 130-140 true (broad reach) with about 10 knots apparent coming over the side at exactly 90 degrees. The boat then does windspeed - it is a really lovely way to sail - we can slip along when there is no chop and go faster than the others who motor. If the apparent goes too far back the boat can slow to 3-4 knots. It is that much of a difference. I love apparent wind sailing in light air and still going deep angles.

    With the apparent coming across the boat at 90 degrees the leeward sail would be completely blanketed by the windward one on a twin rig. Like two boats sailing close side by side, the leeward sail would not have any wind to speak of requiring heading up or down, not just extra sheeting. In dinghy racing you can be beside a boat to windward and fanging along and then when they get to a certain angle, apparent 90 is abeam and you are close - WHAM - you just fall in to windward.

    In one of his books that I don't have any more, Thomas Firth Jones speaks of this problem with his twin rigged cat - Dandy - IIRC he even said that the leeward sail would wobble around in the partial vacuum created by the windward rig and move to windward and touch the eased out leech of the windward rig.

    We need someone who has sailed a Radical Bay to chime in.
     
  2. jorgepease
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    jorgepease Senior Member

    Blanket effect hilighted in red
    Nginrng! http://nginrng.blogspot.com/

    While sloops are fast, their disadvantages make them an onerous choice engineering wise. As I will show in more detail later on, the rolling forces created by the tall sail can be tremendous, and are perhaps the leading culprit for capsize in high-performance sailboats. However, for multihulls there is a more recent and lesser known sailplan which is equally fast (perhaps even faster) and which negates the disadvantages. This rig places two equal-sized sails lined up side-by-side rather than front-to-back, and is called a biplane rig.

    For a given sail area, a biplane rig uses shorter masts and sails than a sloop or ketch, which leads to less extreme pitching and rolling forces overall. At the same time, the side-by-side alignment of the sails further reduces rolling forces by converting them into a sideways drift. Drifting itself is an issue since it shifts the boat off course, but it is still infinitely preferable to capsize, which rolling forces can cause.

    Biplane rigs also share many similarities with ketches. A biplane rig can sail directly upwind like a ketch can, and has similar but superior performance when sailing downwind. The only weakness of biplane rigs is that on a beam reach the lee sail falls into the wind shadow of the windward sail, however this only occurs over a narrow range of angles and has little consequence in practice. Otherwise they dominate virtually every other rig upwind, and downwind their performance is high enough that specialized sails are more of a hassle and a hazard than they are worth. For this reason biplane rigs only rarely ever use jibs or other headsails.

    Owing to their overall high performance, suitability for multihulls, and general ease of management, the biplane rig is my sailplan of choice for the concept designs that I will introduce later.
     
  3. cavalier mk2
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    cavalier mk2 Senior Member

    I don't have time to read this whole thread but what about staggered masts, one more forward one more aft like a schooner or ketch overall but each in its own hull for the biplane rig? It sounds wacky but should work. I'm reminded that a easy way on a cat to adjust the CLR is to stagger the daggers in the hulls, one fore, one aft and play with the adjustments. It must have been a random association.
     
  4. cavalier mk2
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    cavalier mk2 Senior Member

    As Phil points out the range of blanketing occurs over a much wider angles due to the apparent wind shift.
     
  5. jorgepease
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    jorgepease Senior Member

    Here is a good thread on it, sounds to me like the pros outweigh the cons biplane cats http://forums.sailinganarchy.com/index.php?/topic/81486-biplane-cats/

    This from Jeff Schionning on the Radical Bay including an interesting comment on the blanketing issue

    Hi,

    I was sent the comments expressed on this forum by an interested person regarding our Radical bay design. While we do not have all the answers it seems from constructive comments we did not have any of those issues on our cat. Fairly we did not have her for long enough to run into every condition either, but we did deliver her up the East Coast in very rough conditions.

    This was not a windward run but we ran reached and close reached from light to heavy conditions with a well developed sea. We had full sail right down to the second reef which means one sail dropped and the other reefed. Top speed was about 22 knots, air-bourne a few times but an amazing safe feel because of the low center of effort.



    We also raced her quite a lot locally and in the trailerable regatta on Lake Maquarie. Here we had some pretty fast competition with plenty of the Farrier F28R's pushing hard. The RB8 was as quick or quicker to windward but lacked the big kites downwind but still kept up well. We always intended adding screechers but sold her before we had the chance, I feel with these she would be right up there speed wise.



    As mentioned our masts were different to the Thailand RB's so not sure how they balanced. Our RB was easy to tack using the mains as suggested here on the forum, we found her easier in stronger winds 25 - 30 knots but did not have stronger winds to comment above that. The rudders on our RB were in kick-up boxes under the hull, not trasom hung as said. They have a break away release in case of hitting anything.



    She does sail well with the wind forward of the beam as do all multi's but when the wind comes aft and the apparent is 90 degrees on the beam one sail will blanket the other, we found simply dropping the upwind sail right down allowed the windward sail to scoop the wind into the lower sail and getting back to same speed. This is a real safety valve, we found by simply steering to make this shadow happen depowered the boat by half, instant reef.



    This concept like most new ideas will have a heap of knockers trying to derail it but once you sail her the advantages are obvious, of our new Wilderness 1230 design more than half the builders saw this advantage and are going this way. I am also completing drawings for a fast 18.5m charter cat using these rigs. Unstayed rigs are easier to engineer than the stayed rig as there are no hard spots and so safer. We have developed a new fore and aft sheeting system which makes these rigs very easy to control.



    We have the facility to add a storm jib on the cruising cats needed for safe passage making and I feel this will let her tack easily in heavier conditions, if that proves to be needed. Screechers will be normal on these designs and boost power enormously.



    I hope this clears a few issues and with regard to the team Phillips cat, I agree what a shame she died so soon - had good potential for sure. The failure as I followed it was the uni straps running forward on each hull surface to control the side loads of the bow sections were glued onto the surface but the core being honeycomb had insufficient surface area to carry the high load on the compression side, once the strap went out of column well it was all over. The repair solid-filled this area plus added additional ring frames.



    You may have noticed a new RB1060 design out now and a few being built, she can demount to fit into containers and has the option of either rig configeration.



    Regards,





    Jeff Schionning.
     
  6. UpOnStands
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    UpOnStands Senior Member

    "much wider angles" is a bit misleading. If my understanding is correct then for any particular combination of wind speed, boat speed and heading there is just one true wind angle that will trigger blanking. If all variables remain constant then some adjustment might be needed.
     
  7. groper
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    groper Senior Member

    Jeff eludes to the notion its not such a big issue.

    Personally i cant see how 'blanketing' will occur provided the windward sail is not over sheeted and close to stall.

    Consider the high lift devices on passenger jets- leading edge slats and trailing edge flaps. Do the leading edge slats blanket the wing behind it? What about the main wing blanketing the trailing edge flaps?

    What about the 2 element wing masts on the americas cup- does the forward element blanket the aft element?

    So why does a biplane rig windward sail have to blanket the lee sail @ 90deg apparent?

    Why cant the windward sail be trimmed with modest angle of attack and the lee sail sheeted in further to act like a 2 element wing? If the booms are sized so they just clear the other mast- the clearance between them should be very tight and i would be surprised if the system was not extremely powerful in those apparent wind angles close to the beam provided the sailor understood how to trim both sails in those conditions... it would likely appear that the windward sail should be sheeted in more and result in ruining the flow to the lee sail. Minimising sail twist is probably another requirement to this aswell and probably requires the unstayed masts to be extremely stiff in comparison to bendy unstayed versions...
     
  8. redreuben
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    redreuben redreuben

  9. UpOnStands
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    UpOnStands Senior Member

    written by Brian Eiland racing against a Radical Bay in Thailand
    "The twin rigs worked quite well in breeze above 15 knots and they were hard to beat on handicap on those days but they suffered badly in light airs. We observed that the leeward rig gets blanketed a bit on a beam reach but not as much as you would think. This would be worse on a heavier displacement cruising boat, (that particular Radical Bay weighed 1100kg). I was fairly impressed with its tacking ability. It tacked fairly quickly although on the few occasions we cover tacked we noticed the Firefly was faster through and out of the tack. Mind you there are few cats that could tack as well as us.
    The other observation was that it [RB] was a very boring boat to sail, as there wasn't a hell of a lot to do around the bouys. We had kites to launch and jibs to drop at the marks and all they did was ease or trim the mainsheets. Not what you would call an adrenalin rush. I guess my point is, that it certainly would have it's advantages on a cruising boat (ease of handling, etc) but it is not the ideal all round rig, especially for those of us that want to cruise in comfortable conditions ie; under 15knots of breeze, unless you have light, easily driven hulls. One might find the auxiliary gets used a bit more."
     
  10. pogo
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    pogo ingenious dilletante

    Nearly 30 years ago Heinz-Jürgen Sass wrote about his experiences with his biplane-rigg with unstayed rotating masts ( for furling):
    Katamaran - Trimaran - Proa und ihre Technik http://www.multihull.de/technik/t-Sass.htm
    Heinz-Jürgen Sass is a member of this forum , his nick is "HJS"

    But why a biplane ?
    On (larger) cats an unstayed schooner rigg should be possible, see White's mastfoil.
    On trimarans unstayed ketch-, yawl- and schoonerriggs habe been tried - with success.
    See Newick's " White Wings" and " Spark":
    Trimaran Projects and Multihull News: Dick Newick "Spark" trimaran design http://trimaranproject.blogspot.de/2012/10/dick-newick-spark-trimaran-design.html

    French designer Gilles Montaubin has a lot of experience with unstayed carbonmasts, not only on monos !
    One of his trimarans , a schooner, nearly circumnavigated , a Kendrick design has been successfully modified with his unstayed carbonmasts.
    Have a look at Montaubin's boats
     
  11. pogo
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    pogo ingenious dilletante

    Book https://chantiermer.wordpress.com/book/

    Trimar 9 https://chantiermer.wordpress.com/projets/trimar/
     
    Last edited: Jul 27, 2017
  12. Barra
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    Barra Junior Member

    Biplane rigs are SLOW.

    There is now enough data out there for those willing to pull there heads out of the sand.

    Much testing was done using the Stilleto 23 as a test bed, as pointed out by Steve Clarke over on Sailing Anarchy.

    Quote: "Local guy did an extensive two year test of freestanding biplane and ketch rigs compared to a standard sloop rig.

    Hours of two boat testing, systematic data collection and analysis. Lots of attention to detail assuring that weight and trim were standardized across the two boats. In this case Stiletto 23s. Sloop won by a lot on almost all fronts. Not the result he was looking for." Unquote.

    Some here could really benefit from a little class racing , to equip them for understanding what downwind apparent wind sailing and sail trim is all about.
     
  13. pogo
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    pogo ingenious dilletante

    Mmh, enough data ?
    For a few months "Hydraplaneur" was the benchmark , " being slow" she held transat records.
     
  14. jorgepease
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    jorgepease Senior Member

    Yeah that boat is slow!! Too bad they didn't read the SLOW test results before building it and wasting all that money just to break some speed records.
     

  15. jorgepease
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    jorgepease Senior Member

    POGO ... maybe a single unstayed mast in one hull as RD states, a single unstayed mast on the BD needs quite a bit of bury, that means utilizing the salon roof for the top bearing and either a nacelle or higher heavier roof. Putting the mast in the hull keeps it as light as possible.
     
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