Single offcenter rudder for a cruising cat?

Discussion in 'Multihulls' started by rayaldridge, Jul 29, 2010.

  1. rayaldridge
    Joined: Jun 2006
    Posts: 581
    Likes: 26, Points: 0, Legacy Rep: 322
    Location: USA

    rayaldridge Senior Member

    Thom, on Slider, the daggerboard goes down the side of the hull, so only takes up about 4 inches of space on that side. This is not enough to interfere with the seating-- the seats rest on rails that run the length of the cockpits so that the seats can be quickly moved to any part of the cockpit, turned front to back, or two seats can be placed in the same cockpit.

    [​IMG]

    In the new boat, so far I've placed the board in the hull with the two bunks, and it doesn't take up enough room to interfere much with the aft bunk. The bunk flats are about 26 inches wide at the head-- the case narrows the head of that bunk a little. The board will emerge from the side of the cabin just above deck level, so it's well-supported, and can be shorter than a board that extends up through the cabin roof.
     
  2. dstgean
    Joined: Aug 2006
    Posts: 142
    Likes: 5, Points: 0, Legacy Rep: 68
    Location: Chicago Area

    dstgean Senior Member

    Ray,

    How fast do you imagine it will be? 10 knots? 15? On the one hand you mention cruiser with the intent to never fly a hull, and the other you mention Stiletto's and "it's intended to be a much faster boat". Which side of the spectrum do you think it will fall on? Like the idea of the boat though regardless of the answer to that one though, as I think trailerable multis are ideal for lots of cruising folks like myself who prefer to to go fast, stay reasonably level, and have a huge party platform at the anchorage for the size of the boat.

    I've been taken recently by the Dachew's later cats also maned Beowolf that were literally ply boxes with shaped foam (by Micky Munoz) bottoms. Kinda low tech for a really fast boat. Fixed beam and not too trailerable though.

    As for the single rudder issue--there is a loss of redundancy. Most mono's deal with that my making it REALLY bomber. Balance the boat up and you should be able to steer with the sails in the event of rudder loss. Having a rudder on one hull and the outboard on the other makes some pragmatic sense for setup time.

    Me? I'd say anything you can do to get the boat set up quicker is a good thing. Trailering with everything attached is one way to get this thing together quicker too. If the rudder is powerful enough, you won't notice the effect of the altering of the CE/CLR. Like Phill, I do like to have a pair of rudders surfing downwind though.

    How big do you imagine the cabins will be? Larger than the Jones boats? How about compared to the the K650?

    Dan
     
  3. garydierking
    Joined: Sep 2004
    Posts: 191
    Likes: 72, Points: 28, Legacy Rep: 174
    Location: New Zealand

    garydierking Senior Member

    Either move the leeboard aft or move the mast forward, whichever is easiest.
     
  4. rayaldridge
    Joined: Jun 2006
    Posts: 581
    Likes: 26, Points: 0, Legacy Rep: 322
    Location: USA

    rayaldridge Senior Member

    Hey, Dan. I don't know how much faster the new boat will be. I thought Slider was going to be only a little faster than a monohull open cruiser and was pleasantly surprised. But, I figure maybe a lightship weight of 800 pounds, and max displacement of 1800, with about 235 sq. ft. of sail. It's LOA is 19' 8". It won't be as fast as a beach cat, except maybe in heavy air (I'm aiming for a beam of 13 feet.) But it should be able to hit the mid teens in the right conditions.

    The cabins are smallish. But there are two good bunks in one hull, each 26" wide at the shoulder end and 6.5 feet long. The ends of the bunks form seats, with 40 inches of sitting headroom over the flats. The other hull contains the galley, with an 18" deep counter and storage, a two or three person settee with fold-down table, and space for a porta-potti. The galley hull also contains most of the storage, in compartments fore and aft.

    The houses are quite low, if you look at the drawing I posted upthread. They don't need to be very high to give sitting headroom, because the hulls have a lot of freeboard-- the strakes yield the most freeboard you can get out of a 4 foot wide piece of ply. But somehow the narrowness of the hulls seems to take a little of the curse off the high freeboard, visually.

    To sort of give some context, the boat is meant to be about the smallest trailerable cat that could take two people to the Caribbean via the Thorny Path. Not an ocean crosser-- just a Gulf Stream in really settled weather crosser.

    The original concept was for a boat that could be built with a donor rig from a beach cat, and that would still work fine, because. the folding mechanism uses a central spine, so moving the mast would be no problem. But I've had such good luck with Slider's sprit/sloop rig that I'm tempted to do it again. The mast would be cheap to build, and easier to get up and down, and would function well in a tabernacle. (I'm thinking about the EC here.)

    Well, soon the weather will start to cool down, and if a hurricane doesn't blow us away, I'll get started.
     
  5. aussiebushman
    Joined: Oct 2009
    Posts: 283
    Likes: 33, Points: 28, Legacy Rep: 132
    Location: Taralga NSW

    aussiebushman Innovator

    I may be getting senile, but I recall Roger Simpson specifically advising against single rudders, The 9.1 metre Signwave that I built to his plans had twin rudders connected by a simple alloy cross beam. Sure, it is more work to build two and there is a bit more weight but the major benefits seem to be safety in the event of one being damaged also much cleaner and more even flow over the surfaces.
    Alan
     
  6. rayaldridge
    Joined: Jun 2006
    Posts: 581
    Likes: 26, Points: 0, Legacy Rep: 322
    Location: USA

    rayaldridge Senior Member

    Alan, I don't understand why the flow would be cleaner over two rudders compared to one. Could you explain?
     
  7. Alex.A
    Joined: Feb 2010
    Posts: 348
    Likes: 9, Points: 0, Legacy Rep: 108
    Location: South Africa

    Alex.A Senior Member

    You are straying into proa teritory? - Gary Dierking knows this area - good advice?
     
  8. rayaldridge
    Joined: Jun 2006
    Posts: 581
    Likes: 26, Points: 0, Legacy Rep: 322
    Location: USA

    rayaldridge Senior Member

    No, definitely not proa territory. The only difference between this and a conventional cat like Slider would be one less rudder.
     
  9. Richard Woods
    Joined: Jun 2006
    Posts: 2,209
    Likes: 175, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

    How do you plan to steer the boat? Always sitting on one side?? Personally I hate steering from the lee side, especially when its windy or I am sailing fast. And I always sail slower when I cannot see the wind and waves properly.

    But if you aren't going to be on one side all the time how have you designed the tiller?? Just curious

    As far as which is better, one rudder or two, I agree with Catsketcher, as always.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  10. aussiebushman
    Joined: Oct 2009
    Posts: 283
    Likes: 33, Points: 28, Legacy Rep: 132
    Location: Taralga NSW

    aussiebushman Innovator

    Ray - in answer to your question, I probably expressed it badly, but Phil already provided the answer, namely:

     
  11. rayaldridge
    Joined: Jun 2006
    Posts: 581
    Likes: 26, Points: 0, Legacy Rep: 322
    Location: USA

    rayaldridge Senior Member

    I'm thinking about a push-pull tiller. The perpendicular arm could extend to the centerline of the boat, and the tiller itself could swing to either side. Big leverage, at least.

    The problem with a rudder lifting downwind seems like a pretty plausible objection to the idea. How do tacking outriggers handle this problem? Are they more prone to broaching than cats?
     
  12. BriggsMonteith
    Joined: May 2010
    Posts: 58
    Likes: 5, Points: 0, Legacy Rep: 88
    Location: Choctaw Beach, Florida

    BriggsMonteith Junior Member

    What is your objection to a large centerline rudder again? I would think you'd rather have your motor offcenter.
    -Briggs
     

  13. rayaldridge
    Joined: Jun 2006
    Posts: 581
    Likes: 26, Points: 0, Legacy Rep: 322
    Location: USA

    rayaldridge Senior Member

    The idea was to put the single rudder on one hull, and the outboard on the other. One of the problems with outboards and small cats is that usually you have to hang it on a beam, where it's exposed to spray and waves break over it, etc.

    I don't think there's anything wrong with a centerline rudder-- it and a centerline board might be slightly less efficient than a board end-stopped by the hull and a rudder in the entrained water aft of the transom, in my opinion.

    However, this is meant to be a folding cat, and it already has a narrow central spine. You could add a rudder and a case to that spine, but the wider the spine, the narrower the cabins must be. It would also, I think,add weight and complication. The offcenter case I used for Slider (see pic upthread) is simple, strong, and takes up little room. A transom makes a strong mounting point for a rudder.
     
Loading...
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.