Strange double finn

Discussion in 'Sailboats' started by Euler, Jun 18, 2008.

  1. Euler
    Joined: Jun 2008
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    Euler New Member

    Hi everybody!

    Last summer I've see this strang aluminium boat.

    Do you know who is the architect?

    What do you think about those keels?

    What do you think about the curved mast?

    Thank you all

    PS
    the pictures are a little deformed... the boat in REALITY looks less "heavy" and more "sporty"
     

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  2. messabout
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    messabout Senior Member

    It is a strange looking boat. It appears to have three rudders with the center one attached to ??? Maybe some sort of self steering device. The rudder shapes are way too simple to be attached to a boat that shows some other signs of avante garde thinking.

    The bilge keels suggest that it is to be sailed in a heeled mode. But the hard chines combined with vee bottom may not be at their best when heeled.
     
  3. Omeron
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    Omeron Senior Member

    To my eye, she has a purposeful, and industrial look about her. Not too bad if vieved from that angle. Probably intended for extended offshore work, where she is expected to sail on her ear for long periods, steered by a massive windvane. I wouldnt be surprised if designed by a French guy.
    I wonder how those keels extend into the interior of the boat, and how they are structurally secured. When the boat heels, probably the windward side gets out of the water completely, as the leeward side becomes almost vertical.
    Running DDW might be a slow nightmare, with all the cumulative drag of five foils.
    Any engine??
     
  4. Crag Cay
    Joined: May 2006
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    Crag Cay Senior Member

    Marc Lombard has designed a range of multi chine boats for RM Yachts that offered twin keels a bit like those in your picture. (although not as far 'outboard').

    If you look amongst the pictures on this site you will find some pictures.
    http://www.rm-yachts.com/contenu/,rm_1050,42

    I think originally they were offered as the only option, but I think there is now a conventional keel model and less prominence given to the twin keels version on their website.
     
  5. rwatson
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    rwatson Senior Member

    Thanks for that posting. It paralells a trailer sailer design I am having developed, and the twin rudder/fin concept is part of the design.

    It makes me feel a bit less 'out there' with the concept.
     

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  6. RonR
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    RonR Junior Member

    rwatson,
    I like your concept drawing. Some similarities with my Mac 26X.

    Here is more food for thought: At present Iam 'mentally' woking out how move my 20hp ob. rearwards about 10-12". This to allow both rudders to be brought close together (maybe 12" spacing). Benefits could be keeping both rudders engaged in the water, within certain limits. Secondly would enable to unclutter rear deck from steering and power hardware.......Any thoughts ?
     
  7. rwatson
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    rwatson Senior Member

    Hi Ron - its no con-incidence it reminds you of a Mac, it is a direct derivative down to length, water ballast etc with a few other special options.

    full details at
    http://www.boatdesign.net/forums/showthread.php?t=21999
    (I still cant get over the way adobe acrobat can rotate the design through 3d)

    But back to your idea, I dont really see any advantage to bringing the rudders together. At a 12" gap, why even bother with two rudders? You could have just one bigger one. Anyway, you would cut off the already really tight access throught the stern.

    You could mount the outboard on a stainless steel space frame like some dinghies do with their rudders, but that brings in a whole new set of problems with wash, balance etc.

    The whole idea of two rudders is to 1) smaller draft, 2) Room in the middle of the stern. If you 'pop' a rudder on a mac, you are leaning too far anyway. They are supposed to sail flat like a laser.

    If your controls clutter the back of the deck, redesign the controls ( I like the way this other boat has used a 'thru hull' pintle idea.)

    I think the Mac's layout are 'perfect' for their 'class', ( except for the innovations I have specified for my custom version, of course :) )

    I think you should concentrate on less severe innovations of an already well developed design, myself. Like - redesign the whole *&^&&&*^% boat like I am :)
     
  8. Aethelwulffe
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    Aethelwulffe Junior Member

    Geez...

    Uh Guys, you are looking at a setup called a "bilge keel". They are very common in the UK (around the Isle of Wight), Bay of Fundy, and other areas where there is an extreme tidal range. The idea is that when the water goes bye-bye, the boat sits upright instead of falling over. That is the limit of the design. It is not really for heeled performance or any other magical reason. In fact, bilge keels adn twin rudders create quite a bit of extra drag.

    Art
     
  9. rwatson
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    rwatson Senior Member

    "Quite a lot" of extra drag is a bit of a vague measurement. I suppose it could be along the lines of 40% of mono keel/rudder drag, but as far as it relates to 'knots over ground' it isnt a big factor, as hull drag etc is a lot more of a concern
    If it equated to half a knot average, that would be a surprise.
    In areas where the water is 'skinny', that is a small price to pay for not going aground and the accompanying damage. It also means one can take a shorter route around shallow coasts with half a metre less of draft.
    On boats like the MacGregor, dual rudders means you can mount a dirty big outboard, and that means another 10 knots over the fastest sailing speed.
    All in all , a good tradeoff for the majority of boats.
     
  10. lazeyjack

    lazeyjack Guest

    Dunno, But I can tell you that is one very fair boat, some nice work there too, it was not built by any amateur for sure, probably made in Germany, or Holland
    very interesting thanks Be interesting to see how some of our expert people think about the keels Curved mast, you mean plenty of bend, very normal and common, I like that boat, a mans boat and I,ll bet the guy(or woman) is one good sailor, where is she?
     
  11. Aethelwulffe
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    Aethelwulffe Junior Member

    Sure is raining....

    Rained out here. I'm gonna flex my fingers for a while....

    My opinions:
    How is an outboard *ever* a good tradeoff for anything ?:rolleyes: :p

    This boat does not have three rudders. It has one rudder, two keels, and two other foils to keep it upright when the water goes out with the tide and leaves it high and dry i.e. typical bilge keel boat.

    I also feel there is no advantage in skinny water to having a fin keel or any sort of rigid protuberance such as this boat has. It is not a particularly shallow water boat. Stick it somewhere and you are toast....especially if you are in a P.O.S. Macgregor built thing.
    As far as a water-ballast trailer boat, I cannot see why anyone would want to ever go sailing in something that has a ballast density of 1:1, a box-like superstructure that is incredibly unsafe to go forward on top of. Not to mention the utterly hideous appearance, anything with a planing bottom tends to pound in the bay waters that are the only ...I don't say safe, more like "rescuable" waters that such a boat can be on. If you want to run around in a skiff, do so, in a much better manner than you can with a Macgregor. That speed does you absolutely no good when it gets too rough to use it. Then you need a real boat.
    There was a turtled Macgregor 26' WB at Egmont key this spring (Tampa Bay). Coast Guard never got to them, as there were lots of other boats there when the squall came in. Bay News 9 only picked up on the story when the salvage operation started, and only then because they were covering an Formula1 race downtown in St. Pete and happend to notice the fuel slick and the odd boat on it's side. My only other direct experience was one purchased in 1997 by Jack Marcham, an owner (trustee) of the Blue Bell ice-cream company. He wanted to get into sailing (he has a 96' Nordic MV) and he bought the Macgregor when he was at the Houston Boat Show. He hired Don Glandt from the sailing school in the Corpus Christi city marina where we were at to go out with him, and he had me do the commissioning check-over. There were some issues with the brand new engine. Now I had stopped calling myself an outboard mechanic in 1993, and had stopped working on gasoline engines of all kinds by '96, but it is amazing what people will do in the prescense of a Billionare. Corpus Christi has an average daily wind speed somewhere near 20 knots. The outing was a disaster. We could not keep the outboard in the water, we could not keep our feet under us, and we literally could not make it out of the marina quaywall. I am no wilting flower. The chop was just too much. That 40hp yamaha was of no use at all.
    We gave up, put the boat a way, and took Jack out on one of the boats I owned, a very early 70's (read superior construction and better lines/performance) 25' Hunter. It had no engine, as many small MORPH boats there do not. We took it all the way to Port Aransas that day in those very same conditions....In his drunkest moment (what else do you do in Port A but get drunk) he admitted falling in love with the hideous thing (the MacGregor) because it had a windshield like his old chop-top Ford roadster..... He bought it on the basis of asthetics. Some folks should not be left to their own devices.
     
  12. RonR
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    RonR Junior Member

    RWatson,
    appreciate your comments. Very valid. But now I am looking at transferring the rudders also rearwords, and having motor, both rudders(at a 15" pitch) in line and employ a hydraulic cylinder to control all three. I am presently trying to build a case(in my own mind) whereby with the rudders jambed up pretty close to the square transom that the turbulent water coming from below the hull will reduce the effectiveness of about the top 25% of the rudders.
    Don't you think if the rudders are further back in 'clean' water, they might perform more efficiently?
     
  13. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    Are you planning to offset the tillers like they do in multis? The Ackerman angle I believe its called.

    Cheers
    Mbz
     
  14. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    Yes but you must admit its at the limit, the designer could have placed them much further inboard if that was all they wanted to achieve.
     

  15. Aethelwulffe
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    Aethelwulffe Junior Member

    Why place them further inboard? As leeboarders show, the position of the keel relative to the centerline does not affect the performance of the lift much either way. Why then pray tell would you place them far outboard then? Simple: you can support them far better outboard near the chine. Remember that this is an aluminum boat, and this would be a very valid structural issue. You can't just stick a keel in the middle of an unsupported panel. Next, why place them further inboard at all, when you get much better support this way? Why then have them inboard of the chine slightly as they are? Simple, asthetics and the fact that the upper chine panel is not parallel to the keel anyway. The same can be said for the rakish angle they are at. In someone elses words, "sporty" looking, as well as the fact that it is a better angle to support the whole mess on the hard. What is more, though it is pure poo, you can sell folks on the idea that they are magical hydrofoils that actually provide lift. In reality, the hull provides all the lift it can practically use, and any lift those keels provide are just as likely to cause more heeling. An asymetrical or symetrical foil more parallel and close to the surface will generate some upwards lift, while the leeward keel is more vertical in the water and provides the balanced lift of a NACA 00x0 foil profile. Voila, more heel and less righting moment. You will notice that by putting the keels at the upper chine, you have a narrow gap between the hull and the upper portion of the blade. That will tend to make it act as an asymetrical foil.
    All this said, all the choices made in this design seem to be practical for one goal, modified for asthetics, and supportive of any BS a broker/salesman may want to dream up about it. The drawbacks are that it would be a horrible boat to RUN aground with...aluminum and rocks and high speed and all that...
    I do have a retraction to print there though...those are certainly three rudders. The outboard rudders seem to be supported in a manner that would allow them to support the boat should the boat be over an uneven bottom when the tide is out. The center rudder that looks like it was stolen off of a dinghy is directly attached to a steering gear. It is strange to me that they did not use the position to mount a servo pendulum style gear to control the main rudders. I think this boat will need a LOT of steering. An SP gear gives the most power, blah,blah,blah.

    As far as rudders that are very far aft, they can give you lots of power, but they don't give you good response. You also can't use them well under power with no way on. At very low speeds, you get more effect from a low aspect ratio rudder at a high attack than you do from a nice high-lift foil that otherwise rules the roost. Another problem with rudders in "clean water" is that you create more tip vorticies, i.e. drag in an asymetrical fashion, which leads to weatherhelm, which leads to more drag, which...does add up to something significant, speed, yes, but other factors like course stability as well.
     
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