Multihull manuverability

Discussion in 'Multihulls' started by rapscallion, Dec 28, 2011.

  1. rapscallion
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    rapscallion Senior Member

    I have a question:

    How does one design a multihull to be maneuverable? Specifically, how do you get a multi to tack quickly? Is it simply adding rocker? Pulling up the daggerboard(s) during a tack?
     
  2. CatBuilder

    CatBuilder Previous Member

    The best way to get a multihull to tack properly is to make it faster.

    What happens in practice is that a multihull quickly loses forward momentum once you enter irons. I suppose it has less momentum because it weighs less.

    Anyway, it can't continue the tack on its own like a keel boat can.

    Once you take the power (sail power) off, it quickly drops in speed, so through the tack, it slows down very quickly. It also presents a lot of surface area to the wind, which slows it down as well. Fat hulled multi hulls present a lot of hull area to oncoming water too, so they slow down even worse.

    If you are having trouble tacking one, try your technique first...

    If close hauled, fall off just a little bit and get some speed up, then initiate a fast, smooth tack.

    If on a reach, do one sweeping, bold, hard tack from beam reach to other beam reach. There is no time to do a tack slowly on a catamaran. Forward momentum is lost if you do.

    Hope that helps.
     
  3. gonzo
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    gonzo Senior Member

    Any lightweight boat with a lot of windage has a hard time tacking. Speed is a solution. Another centuries old technique that works well is backing the jib when you are in irons.
     
  4. Doug Lord
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    Doug Lord Flight Ready

    ===========
    Speed and a long daggerboard. Why? Made dozens of RC model cats as a kid and since-also designed and built a couple full size small cats and tri's-the number 1 thing that improved tacking was a high aspect, deep dagger board.
     
  5. gonzo
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    gonzo Senior Member

    The daggerboards help tacking, if you pull them up the boat will drift sideways.
     
  6. Richard Woods
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    Richard Woods Woods Designs

    What kind of multihull are you talking about??

    An A class cat? An AC45?

    A Catalac?

    I've seen lots of multihulls tack faster than monohulls. Watch how fast a AC45 helm has to move across the boat to get to the other side in time.

    Or look here, taken from the FAQs page of my website which goes into windward performance and tacking in more detail

    http://www.youtube.com/watch?v=EZ99i9ebzh8

    Fast enough I think, even with one crew doing nothing.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  7. CatBuilder

    CatBuilder Previous Member

    That's a good video, Richard. You have to admit cats are a little more squirrely when tacking though, right?

    Even in that video, that's not as "sure footed" of a tack as you get on a heavy monohull. There is more drifting, more of a loss of forward momentum.

    PS: I had a good laugh at your example of the opposite of an AC45! ha ha ha :) I sure know what you mean there, from experience.
     
  8. rayaldridge
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    rayaldridge Senior Member

    I don't really know why, but my little cat Slider tacks very reliably if a bit more slowly than a heavy mono. She will tack in any conditions and with any sail combo, daggerboard up or down, and without any special technique. I somewhat tentatively consider that she does so well due to a little extra rocker, and big rudders.

    Here's video that shows her tacking under main alone and with the board up:


    http://www.youtube.com/watch?v=_OCnSN-6kcY&feature=mfu_in_order&list=UL
     
  9. Richard Woods
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    Richard Woods Woods Designs

    My brother has a 24ft fast monohull. It does tack a bit quicker than my 25ft catamaran (which tacks faster than the 25year old 35ft Banshee seen in the previous post). The first time I sailed his boat I was steering and let go the helm for a second to pick up a coffee cup. The boat immediately tacked

    So no way that it can do this

    http://www.youtube.com/watch?v=pfd5YTUEDMM&list=UUhKTQtbKN5BaXFTg2BjcbqA

    It's a compromise. However most will agree that it is better to have more directional stability than high manouverability

    Watch some multihull race starts and you'll see they are just as manouverable as the monohulls. Only they take up much more space. Having a big crew on a monohull obviously speeds their tacking. I would say that a 35ft monohull will be no faster to tack with only three crew than the Banshee

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  10. Boston

    Boston Previous Member

  11. CatBuilder

    CatBuilder Previous Member

    He took a big loan out to fill that win column. Ol' Poseidon will surely want that back, plus a usury interest rate.
     
  12. rapscallion
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    rapscallion Senior Member


    Is that true for any given sea state? The reason I'm asking all of these questions is there is currently a debate at our local yacht club about Monos and Multis racing together... Obviously, i want to race. I also don't think monos and multis shouldn't race against each other per say, monos and multis should have their own fleet.

    But one of the concerns brought up was safety.. specifically that multis are less maneuverable than monos, and so a mixed start is a bad idea.. so the 2 multis will most likely get their own start... which is fine... but I personally don't necessarily believe a well sailed multi is less maneuverable
    than a monohull... but I'm told by a couple of local multisailors that in chop, larger multis tack painfully slow... even with the tricks like boxing the jib and falling off first to gain speed... It's good to hear richard say some good things about maneuverability though... I guess it's something I will have to learn with experience.
    I'm just trying to gather some info on the topic that may help me in some of those discussions.
     
  13. rayaldridge
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    rayaldridge Senior Member

    That depends on what multihull we're talking about. Most tris are almost as easy to tack as a mono, but some cats are less handy.
     
  14. Richard Woods
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    Richard Woods Woods Designs

    Multihulls are always welcome in the PNW. Check out, for example, the Cowichan Bay (Cow bay) regatta in BC, Canada. Typically 100 boats racing from ULDBs (SC52 etc) to Flying Tigers etc. 20 will be multihulls, all very competitive. But we start first because, as I said in the last post, it's a short, crowded start line especially with boats 20ft wide instead of 8ft.

    The fastest monohulls start 10 mins later and if it is over 15 knots wind they don't catch up on the first beat. If it is under that they do.

    Also check out the Round the Island Race in the UK. Typically 1700 boats in several starts, and 50+ multihulls

    Having said that I would recommend that the multihulls start first (you get clear air that way!). That's the norm.

    If the multihulls start last it can be quite dangerous. Primarily because most monohull sailors don't appreciate how fast multihulls sail, nothing to do with maneuverability

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     

  15. keysdisease
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    keysdisease Senior Member

    Far freakin out!! Those Aussie's have it going on with Cats, and sometimes its better to be lucky than good

    Steve



     
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