Main-less rig

Discussion in 'Multihulls' started by Spiv, Feb 10, 2008.

  1. Spiv
    Joined: Jun 2007
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    Spiv Ancient Mariner

    Hi everyone,
    I mentioned a few times that I was working on a new(ish) design for a cruising rig, a rig that I though off since I built a 12.5m cat in 2002.
    Basically my cat cannot be sailed with the main only; now, I know that others can, however this is not the only point, what got me thinking is:
    1.Mains can only be reefed upwind (where there is more wind), this can also be dangerous if you were running and left too much canvas up too late and, is never a one man job.
    2.The boom is a real nonsense, jibing more complicated than headsails.
    3.Even with lazyjacks, it is not that easy to get rid of the main.
    4.But the most significant thing is that the mast turbulence affects the first part of the sail: the most important part as far as efficiency is concerned (see C. A. Marchaj).

    Another thing I want to do with my next boat is go up rivers and visit cities, this is when you need to go under bridges, powerlines and other obstructions. A properly engineered tabernacle a winch and a couple of poles will let you lower the mast, but it is a precarious situation, power boats going by can cause havoc, even injuries or damage.

    So, my first thought lead me towards an “A” frame mast with a furler in the middle for the main and one or two up front for the jib and the screecher. That way I can reduce sail downwind and the mast is not in the way.
    The two masts only work in compression, so do not need to be so strong as the normal mast that is not only compressed, but also wildly twisted by the main.
    No need for shrouds, chainplates etc.

    The hull needs to be engineered differently as now there is tension in the middle rather than compression, the rest is as any other cat.

    This was my line of thought until I bumped on Brian Eiland “Mast-Aft” rig: a mizzen sail on a wishbone boom! What a great idea!
    For all the many benefits of such a rig, please read Brian’s article on his design here.

    Some points to consider:
    5.If the mast is stepped aft and inclined forward, it will protrude less from the bow when lowered.
    6.Also the main (jibsail) can be self tacking.
    7.Not too far back as the backstays need some angle, perhaps they could be on a targa bar.
    8.The boat is a 13m cruising cat on 15~16m long hulls. Composite vac-bagged sandwich, 7~8 ton + 3ton gear.
    9.The sails could be 70, 50 and 50sqm or thereabout, that will give a lot of canvas for light winds.

    Forgive the crude drawing, I draw it in MS Word.... I downloaded Freeship and was going to design this rig myself with the final touch by the Naval Architect whom will also design the hull, but it will take time to learn Freeship, so since I discovered this forum and realized the talent that is behind all you guys, maybe we can design this all together and if it performs well we might make a change in the way the world goes sailing…. Or at least the cruising world.
     

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  2. brian eiland
    Joined: Jun 2002
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    brian eiland Senior Member

    Thanks for the 'heads up' Stefano. At the moment I'm over in Thailand looking at a couple of projects. The internet connections here are really slow, so I may have to delay some of my participation on this subject thread until I return to USA, but I hope others join in.
     
  3. TeddyDiver
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    TeddyDiver Gollywobbler

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  4. yipster
    Joined: Oct 2002
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    yipster designer

    hi guy's, maybe its me but i cant read the drawing well, A frame and than a wingmast with wingsails like i envision? no thats not what you write but i see 2 foils straight down no? i'm sure you enlighten me further in some more detail, let me just mention here a wingmast can be lightweight, has a big area and dont buckle or bend easy when loaded undiamonted. i like the striking mast idea, see my gallery for a full transition to motorcat, but not only for going inland, a downed mast doesnt rattle and howl at night witch is nice. inertia, like in a mast, may be good giving a slow dynamic movement but is an absolete burdon when not in use, in a cat beeing out in rougher weather with the sails reefed i'm sure your rather have your (wing) mast down too when easely done. somehow i imagine a well designed A frame with striking possibility on open water, i think the stay's seems to allow for that in an A triangle or am i thinking way too lightly on that? anyway, more thoughts to follow and planty to figger out and discus :D
     
  5. Nordic Cat
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    Nordic Cat Senior Member


    Hi Stefano,

    I guess this all brings us back to the "design triangle" with comfort, speed and price..

    For your requirements of being able to efficiently lower the masts, i think the "A-frame" mast offers a great solution.

    I well proven fact is that the high Apspect Ratio rigs are more efficient.
    Foresails when used with a main interfere and therefore bring down total rig efficiency. The upside is that they can easily be furled.
    So based on these facts, if you will accept a lower rig efficiency, that means less performance, then a mast aft rig could be a solution. I think an A-mast rig is a better solution than a mast aft rig but maybe because I'm just an engineer....

    Have you considered using two narrower A-masts? One on each hull, with an horisontal "strut" to attach a traditional boom to. The "strut" could also be the hinge for the whole mast, and also be the attachment point for the stay.
    These masts could be quite far forward, and swing down to the stern, rest them on a wide targa. The forestays can have a Code 0 that furls without a foil,or a jib.

    I know its 2 masts, but they can be made very light by having horisontal struts to stiffen them. Easily a one man job to raise and drop via an electric winch. If you have the "hinge" 2 meters over the side deck, a mast height of say 16 meters, then maybe only a couple of meters will be behind the boat when laying them down.

    Regards

    Alan
     
  6. yipster
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    yipster designer

    hi Alan, forgive for speaking out of turn. iff i understand Stefano's concept now that are triple furling jibs between a bare A frame? offcourse your right above with comfort, speed and price yet i wonder how much. as i see it the two masts may be wingmasts taking the drag and vortexes away. have a high aspect, speed served against not to much cost. there is however something to say for low aspect as well but that i have to study closer. always liked a cool drink under a tent over a striken masts and why not on a targa, has to be strong tho. a step further flush down in gangboard masts give more lenght, lower cg and look good too, a bimini for the cool drink than. i looked at horizontal struts but belive they take the strenght out of the triange concept and need lots of draggy wiring. only whish i was a engineer so please correct me if i'm wrong. yes, belowdeck electric winching the say 2/300? kilo matsts but miss how a strut can be the hinging point.
     
  7. brian eiland
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    brian eiland Senior Member

    Wishbone Shaped, Bi-Pod Mast

    I might make the suggestion that everyone interested in this subject should review this subject thread:
    WishBone Sailing Rig

    ...and consider this variation:
    http://www.boatdesign.net/forums/showpost.php?p=109336&postcount=34

    I would also encourage review of "Procyon..a bold experiment"

    ...and pay attention to what Olaf Harken has to say about the 'connection' of the bi-pod mast at the masthead;
    http://www.boatdesign.net/forums/showpost.php?p=112067&postcount=33

    That factor was to influence my thoughts to make the bi-pod mast a single tube above the aft jumper, as well as the extra difficulties associated with controlling the twisting forces that would result from a divided aft jumper and the inner staysail attachment point.
     
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  8. masalai
    Joined: Oct 2007
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    Location: cruising, Australia

    masalai masalai

    Aaaay Spiv,
    I have promoted him in absentia & will do it again (#3) John Hitch recently of Queensland, has built himself another boat and is back cruising somewhere?

    His concept is a single mast with a genoa on roller-reefing to each bow of his cat and I think a "blade" of storm tri-sail midships. Most cruising is downwind or thereabouts so pointing ability is not critical. (Motors, or an anchor, are the appropriate remedies for upwind times.) Too Fishing easy...

    I would suggest, you only need a single sheet for each sail. If you need to tack to the other board then roll up one and let the leeward sail out. It also gives lift to the leeward hull (not driving it down into the water?). Downwind wing and wing both (using spinnaker poles) and a small flat cut spinnaker between the two forestays/genoa...
     
  9. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    Bi-pole rig not that light

    Hello Spiv

    One of the reasons the bi-pole rig is not well patronised is that to carry compression loads with two columns will always be heavier than using one column. This is because the compression carrying capability is is dependent (among other factors) on the second moment of area of the column. This goes up by the power of four as you increase dimensions. This means that you will need not just two masts of half the weight but probably two masts of about 70% the weight each.

    Reefing downwind can be done on a pretty normal rig. I can reef my 38ft cats main reasonably easily but it does take about 5 minutes to take in a reef. My rig has a wishbone and does not use diamonds - it has three stays per side and an inner forestay. This means the main doesn't catch on the spreaders or diamonds downwind. To reef ease a metre of halyard and winch the luff and the reefing pendant down alternately. Then repeat until the reef is taken in. It works fine.

    I love my rig and feel that it is important to have a simple easy to use rig that is also pretty efficient. The inner forestay carries a storm jib when going to windward over 20 knots when cruising offshore, the wishbone takes all the leech loads - very low sheet loadings and a tame rig to use.

    Remember that you may want to go to windward pretty well. ON the East coast of Oz you often have to bash your way south from Lizard Island until you get to where the northerlies are - often you chase them along way south hard on the wind. Mainsails with small blade jibs go to windward beautifully in tradewind conditions. Unless you have oodles of time to wait (maybe months) then you will often need to go to windward really well. A normal modern sloop rig really does well here.

    cheers

    Phil Thompson
     
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  10. DanishBagger
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    DanishBagger Never Again

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  11. Spiv
    Joined: Jun 2007
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    Spiv Ancient Mariner

    I sailed alongside this 50'(ish) cat on my way down the Wast Coast in 2005. A bit spartan accomodation, but she was sailing well.
     

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  12. Spiv
    Joined: Jun 2007
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    Spiv Ancient Mariner

    Interesting design, however I need to be able to easily lower the mast.
     
  13. Spiv
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    Spiv Ancient Mariner

    Problem with that is that unless they are rotating, they will present the wide side to the wind most of the time.

    isn't that what cruising is all about....
     
  14. DanishBagger
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    DanishBagger Never Again

    I'm thinking you could stay it (there are many stayed lugsails out there), and have it deckstepped with a (the world escapes me right now) "huge hinge" to let it go down easily. And if combined with hardware* from precourt.ca, it would be easy and quick to do so.

    *I guess one could call it "software" instead, haha:

    From www.precourt.ca
     

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  15. masalai
    Joined: Oct 2007
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    masalai masalai

    Spiv, Go to RPYC (sort of next door to PFS - where I used to sail out of) and yachts such as "Siska" and other biggies used to drop the mast quite often for a weekend over "Rotto". . Having two roller furling (don't need reefing)genoas would not make much hassle in regular stick dropping with a solid is it "Tabernacle"? like Danish - forget - I am getting old... and a couple of spinnaker poles....

    The other way is to carry a couple of beach-cats (14 ft) for stable tenders, put the stick up once up the Swan for the fun of it - and to pick up some nice Swan valley plonk...:D

    That 50 ft could have been John - He does not believe in clutter or any form of un-necessary stuff on a cat.
     
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