retrofitting boards to an old cat

Discussion in 'Multihulls' started by DirkP, Feb 18, 2010.

  1. DirkP
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    DirkP Junior Member

    Hi all,

    I was inquiring about the possibility and the advantages of upgrading/modifying the rig on an older cat in another topic http://www.boatdesign.net/forums/multihulls/new-rig-old-cruising-cat-31520.html

    I immediately got a response saying one could retrofit daggerboards which would make a very big improvement in the windward abilities.

    Apart from the technical implications to perform such a modification, daggerboards or centerboards mostly have their boxes housed inside the hulls, would you think such an upgrade would be worthwhile ? Any idea what improvement we could get from this ?

    Remember I am talking about the older first British designs, Oceanic, Catalac, Ocean Winds etc... (by now most designs have boards or keels to help prevent leeway)
     
  2. DirkP
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    DirkP Junior Member

    To complete the things said in the other topic, another option was pointed out, no clue if this has ever been done but it does make some sense to me...

    I stand corrected, the Ocean Winds 33 has keels (but still windward could be improved)
     
  3. sandy daugherty
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    sandy daugherty Senior Member

    David Gerr says that leeboards have some significant advantages. They have more foil in the water for a given draft, and don't eat up interior space. They kick up when needed, and (my thought) can be assymetrical for greater lift to weather. If you have a conveniently located bulkhead, the engineering should be simple.
     
  4. DirkP
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    DirkP Junior Member

    Thank you for your view Sandy !

    You got me thinking now, I'm sorry, trying to visualise what you're writing...

    Do you mean leeboards carried next to the hulls ? (that's what I understand under 'leeboard' as I know from the Dutch Barges)
    [​IMG]
    Indeed these kick up when grounding...

    Where would you install these ? Convenient bulkhead ? Can you elaborate just a bit please ?

    Thank you !
     
  5. sandy daugherty
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    sandy daugherty Senior Member

    I think the additional structure to carry the loads a leeboard would generate would be excessive unless there is already a transverse bulkhead that could support the axle the boards rotate on. I assume that there would be a strake on the hull that the board would ride against, but there would still be a lot of forces (moments) to contend with. I suggest that any of the Prouts would be ideal candidates for such a mod, but the performance increase would be modest because of their weight and low bridgedeck clearance. Catalacs would not be candidates because they have no shoal keels to lose!
     
  6. djeeke
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    djeeke Junior Member

    What about the keel system already installed on the Oceanic ?

    Just a sketch as I don't have any good picture at hand :
    [​IMG]

    Does anybody know if this worked ? Anybody has any information on these ?
    I guess they were not as effective as the designer hoped for as I have been told they stopped installing them on later builds (can anybody confirm?) ...

    If this is effective it could be copied over to other boats...

    To me however, this means that even if they have no keels to lose, windward sailing of Catalacs and Oceanics and other keel-less designs could be improved with additional boards.. (so this topic would count for boats with and without keels)

    Sandy, performance increase modest due to weight and bridgedeck clearance ?
    - I suspect you mean a board will be less effective in reducing leeway of a heavier displacement boat.
    Or in other words, if the boat is heavier, the surface of the leeboard will need to increase to stay effective.
    - How is bridgedeck clearance related to leeway ?
     
  7. sandy daugherty
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    sandy daugherty Senior Member

    I don't really have a dog in this fight, but by performance I meant all-around performance up and down wind, winter and summer, etc. If a boat loses headway in a series of slaps, it won't matter what kind of a keel it has. If a boat has much more wetted surface area than another, VMG(w) won't cause heart palpitations either.

    I once laced a short paddle to the side rail on my Hobie 14, and thought it made a difference, but I still couldn't keep up with the flat-bellied kids who could hike out for an hour at a time!

    I don't have a clue how big or deep a leeboard would have to be; its just an idea!
     
  8. djeeke
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    djeeke Junior Member

    Thank you Sandy, I got your point on this one :)
    One can lose heading in many ways... A series of slaps, even just one it it's enough to stall the boat (I experienced this myself on an Oceans Winds 33, change of heading cured the slaps and the stalling...)

    I have no dog on this fight either, let alone a cat ;-)))

    I wonder indeed how dimensions for boards are defined, somebody on this site might have an idea though...
    Or are people just playing trial and error starting from what seems to work on other boats ???

    There seem to be many theories on boards, some even advocate just one single board in or on one single hull will do just fine, others prefer dual boards, even asymmetrical ones as suggested earlier here.

    Here is a boat of that era that does not need this addition, it was designed with centerboards... The Iroquois... Which even today seems to do well sailing windward... [​IMG]
    From the others, I understand the Aristocat was built with centerboards or with keels... (on customer's request?)
     
  9. RHP
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    RHP Senior Member

    When I read the title I thought you´d bought Alinghi......
     
  10. sandy daugherty
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    sandy daugherty Senior Member

    Board dimensions and keel area are largely in the realm of a Naval Architect. Somebody somewhere will have a formula and will be glad to help anyone with the courage to cut the keels off a shoal-keeled cat, I'm sure. But a word on centerboards, a term properly limited to a keel that hinges up into a slot in the center of a hull.

    Four boats ago I had a Stiletto 30 with centerboards. They worked well at resisting leeway, but have fallen into disfavor for these reasons:
    They are difficult to build: the trunks must be very strong to carry the loads, and the boards must fit snugly to keep from pumping lots of water up in the trunk. The hinge mechanism is an additional complication requiring frequent maintenance, and sensitive to garbage (sand, pebbles, barnacles, seagrass) that invariably sneeks in. The open slot is a source of drag and turbulence, and efforts to seal the slot with covers are usually unsatisfactory or even disastrous. Retraction cables, hold downs, pull-downs and more add to the mechanical complexity and potential failure points. And finally, running into some obstruction backwards, as you might in irons, is a catrastrophe.

    But the real reason we don't see many centerboards any more is that they are just too expensive to build. Dagger boards are, relatively speaking, a piece of cake.
     
  11. sandy daugherty
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    sandy daugherty Senior Member

    No, RHP, that was Dirk. I'm negotiating with Oracle. I want them to ship it by air.
     
  12. djeeke
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    djeeke Junior Member

    Hi Sandy,

    I agree that dimensions are within the playground of the architects, but it seems we are the only two people talking here (apart from the thread starter) and I hope to get some more reaction...

    I was hoping someone else would join the discussion, as I think this is an interesting one and to some point I can even understand what I'm talking about :cool:

    Yes, I know the centerboard is a concealed leeboard, that's why I posted the Iroquois drawing with it, it is clear the board hinges back inside the hull.
    As you stated they require more attention than daggerboards and the concept has its major drawbacks. (more complex mechanics and requiring more maintenance)
    As much as I believe they are a good solution, this is clearly a no-go for retrofitting to a boat. They must be designed with the boat...
    I did mention the Aristocat, I believe this is the ancestor of the Gemini who still produce centerboard cats...

    But let's get back on topic and to the (drawing) (lee) (dagger) board... (pick one :D )

    I'm also curious to see if anyone cares to comment on the keels of the Oceanic ...
     
  13. Richard Woods
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    Richard Woods Woods Designs

    I wouldn't do it

    If you buy an old Oceanic and then spend a lot of time and money on adding keels you still have an old Oceanic that no one will want to buy because it has been modified.

    Obviously adding a keel is a lot easier than adding daggerboards, which go through the accommodation (galley, chart table?) which would need refitting as well.

    Also remember that the rig was designed for poor pointing ability so sheet leads will be wide compared to a daggerboarded boat, so you'd have to change that. Which probably means moving the chainplates inboard, which means new bulkheads and new interior, never mind reinforcing the deck.

    I don't think the Oceanic angled keels worked. The Oceanic sails a lot worse than a Catalac.

    A friend delivered one once. I met him half way through the delivery. He said "hey, it sails well"

    Then he had to go to windward instead of sailing downwind. After the trip was over he said "Never again"

    Hope this helps

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  14. djeeke
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    djeeke Junior Member

    Did some looking...

    What exactly are you looking at improving Dirk ?
    Any specific boat in mind ?

    The Catalac won't be the boat asking for this kind of improvement, I ran into an old article stating it happily tacks through 90°, even a bit better if required... I can't see a Catalac owner going through all these efforts of building ans installing boards to gain a few degrees (if any)

    So yes, maybe the Oceanic as Richard mentions, from the little feedback I have on this boat it seems to tack through 120° at best... (if anybody has more info and this is not correct, please let me know, this is just what I've been told!)

    What Richard mentions is important, one would look at more changes than you initially think of...
    Install boards and reduce leeway.
    Then find out you can't trim your sails and need to rethink the whole rig configuration...

    I guess Richard is right, it's not worth the effort... So I would say the Oceanic is a motorsailboat especially to windward...
     
    Last edited: Feb 20, 2010

  15. sandy daugherty
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    sandy daugherty Senior Member

    Someone once put a cabin and codpieces on a MacGregor 36, so common sense isn't universally common. Let's just say for the sake of discussion that there is an older design with shoal keels that someone already owns who just has to point better. This idea (which I'm not about to defend) only occurred to me because I'm reading Dave Gerr's "The Nature of Boats; Insights and Esoterica for the Nautically Obsessed" We have similar writing styles so I'm finding it very readable, if just a little hard on multihull stability. I think he did design one, though.

    Richard; you are as you should be, imminently practical! Spoilsport.
     
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