Daggerboards or bilge keels on cat.

Discussion in 'Boat Design' started by Landlubber, Apr 21, 2010.

  1. Landlubber
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    Landlubber Senior Member

    I have just visited a friends boat he is finishing building, a Schionning 14 M.

    We were discussing the daggerboards, and the need for them.

    Is there any reason that we could not use mini bilge keels instead of the design daggerboards. There is much complication in raising and lowering them and the possibility of jamming that could be averted by simply making some long bilge keels of larger than the dagger board areas.

    Comments please for or against and why.

    Ta, John
     
  2. fng
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    fng Junior Member

    very interesting and debatable question.
    So here's my 2 cents worth. Prior the resession we were about to imbark on at 14.5mtr cruising cat build. Which envolve a lengthy tour of Queensland and NSW in Aussie. The designer of our choice ended up Grainger, with his Catmando design ticking all the boxes. We spent some time with the owners Mark and Rem. There coments and observations were if you had a racing background and were mostly conserned about point A to B sailing then go for dagger boards. If you were fast cruising orientated then mini keels were the go hands down.
    They gave an example of a friend with a shoinning 14 flash sails minimal interior and dagerboards leaving a bay at the same time they did, they watched them hoist then tack and tack to get around the headland, while Catmando motor sailed with a headsail unfurled. They reached the headland just before the S14, hoisted there main and beat them to the next anchorage.
    Other points are you can still beach with mini keels, and the cat is at a much better altitude for mantinace and antifouling, than sitting on its bum. No centre cases, no lifting cages and gear.....
     
  3. Fanie
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    Fanie Fanie

    Dear John :D,

    I like daggerboards as they should be the pivot point for when you tack.
    I also suspect you can sail better to wind with them.
    Your draft is shallower with the boards raised, a big advantage in many places.

    If your handling them seems complicated I'm almost sure there is an oversight. They should be simple and easy to operate. Two lines, one pulls down, the other one raises it. If a line is in a pipe it cannot jam.
     
  4. Landlubber
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    Landlubber Senior Member

    "Your draft is shallower with the boards raised, a big advantage in many places."...wrong, the rudders are the lowest part of this design...mini keels would protect the rudders and allow the vessel to sit on the hard...

    Yes I reaslise that the dagger boards would be the fastest version, but in reality what is lost with bilge keels, another friend has done the concersion on a cruising cat and it sails exceptionally well.

    What I am looking for please is a technical answer if there is a designer out there that can say why we should not do the mini keel version, it has a lot going for it so it seems.
     
  5. Landlubber
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    Landlubber Senior Member

    Fanie,

    These dagger boards are seriously large, not hand held funny things that can be pulled up and down, they are over 12 feet high and need to be winched anyhow.
     
  6. Fanie
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    Fanie Fanie

    If you beach on a rocky shore you will damage your boat in any case. I prefer the dagger boards to mini keels. I also like the choice to have them lowered or up, depending what you do. Your rudders should be made to lift imo. If you want to beach you lift the daggerboards and the rudders. My rudders will be abe to flip up if they hit something underwater. Best to beach would be to lift the daggerboards and rudders and use the outboard to get you where you want to be. Remember the tide or you may get stuck :D

    In rough weather you can use the windward dagger board down to keep the boat from capsizing or sliding. Hopefully something one never have to use. The leeward mini keel may see you trip over it.

    If you run you lift both daggerboards and you gain a bit of speed.

    If your boards are too heavy then yes, you have to use a winch for them, or have the wife lift them so you won't hurt the back ;).

    If they are that heavy, at least letting them down is going to be slightly easier.

    Mini keels are long things, the will probably affect the ease with which the boat tacks. The daggerboard makes it more like a pivot around which it will turn, or try to.

    You asked, I give you my opinion. Any one else can give their opinions.
     
  7. fng
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    fng Junior Member

    I recall a while back see a french artical on them ( eric louroge, I hope thats how you spell it ) Basically the higher aspect daggerboard is better but the jist of the artical was not that much better for a crusing cat. If you look at Grainger designs you will find most of his crusing cats have mini keels, yet he still designs race winning cats with dagger boards. In our aussie travels we met a couple building a oram design with 1 daggerboard in 1 hull. It really depends weather or not you want to be able to beach the cat on its hull bottom or not for cruising. Have a look at http://catmando.co.au/default.htm
     
  8. fng
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    fng Junior Member

    pics I hope
     

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  9. Landlubber
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    Landlubber Senior Member

    yeah, thanks fellas, many designers will show outer than dagger boards, Schionning doesn't...I guess we will just have to design our own and go for it, similar to the Grainger shapes. I guess the centre of resistance for the mini keels is still mid point as per the dagger board mid point.
     
  10. messabout
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    messabout Senior Member

    Decision between the two methods should be considered in light of where and when you sail. If you are to sail considerable distances to windward then the boards are superior. 200Km of windward work will make you wish the boat would hold on better. If it is only 2Km then there is no bother. If most of your work is from close reach to full run then the bilge keels will be adequate.

    The term daggerboard has been used. It is 12 feet long? The Yank term for daggers is that it is a board that is inserted in a hull through a slot. It is not a pivoting board. That kind of board is indeed a dagger like thing. The pivoting variety is a centerboard even though it may or may not be located at the centerof the hull. One of the serious downsides of a centerboard is that the housing intrudes into the interior of the boat. Also there is a long slot in the boat bottom that causes drag, accumulates all sorts of trash, sand, pebbles, and such. The pivot pin outlet, on the sides of the housing, is a famous place to develope leaks. The housing, (we call it the case), is problematic in the structural sense. Say that the board is 12 feet in length and has a 2 foot chord. When lowered there is a 5 to one lever doing its' best to twist the case. One must address all that stuff during the decision making process. Performance gain versus a cleaner, less involved, set of bilge keels.
     
  11. tunnels

    tunnels Previous Member

    If you are building a cat that has the potentual to sail quickly and get you from point A to point B with out to much fuss and bother why the hell strap in a few hundred kilos of lead on the bottom to slow it down .
    You spend all that money on big sails and tall masts to make it go and then run round everywhere with the hand brake on , sound like a dimb idea to me. If you hole the boat do you want the boat to sink quickly so now one will see what youve done ??
    Do you believe in out of sight out of mind !!:p
     
  12. Landlubber
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    Landlubber Senior Member

    tunnels...where has anyone mentioned lead, cats generally are not weight ballasted....

    messabout, yes they are dagger boards currently and already built, I became involved and simply asked why not go for mini bilge keels as the boat is going to be a cruising boat, even though it is reasonably light (6500kgs) for the size it is still a cruiser, liveaboard.
     
  13. waikikin
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    waikikin Senior Member

    I've had mini keels on a cat & they were a pretty valid option especially as they incorperated fresh water tankage & protruded about 4-5" lower than the fixed spade rudders & also offered some protection to these. My next cat is to have daggerboards, at some extra complication but hopefully higher performance. The minikeels on some cats like seawind 850 & 1000 & maybe others are glued into molded sockets in the canoe body of the hulls, the vessel I had the keels were glassed on, the Hitchhiker cats had alu minikeels also as tankage & in this case bolted on.
    Have whatever suits You. All the best from Jeff.
     
  14. Typhoon
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    Typhoon Senior Member

    Skegs/keelsons merely long and deep enough to allow stable beaching of the boat combined with centreboards.
    Friends had a Eureka 32, the centreboards had enough buoyancy they could be raised by merely letting a rope jammer go. Also, design teh cases so you can lift teh boards out the top with the boom and a rope for maintenence.
    Keep it simple, work out what you NEED from the keels and design the bare minimum for your requirements.
    Anything more is just excess weight and drag. Centreboards make cats much more manouvreable, something they need badly.

    Regards, Andrew.
     

  15. Landlubber
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    Landlubber Senior Member

    ....Ok thanks fellas, I will report back to my mate and he can make the decision...thanks again for all the comments.
     
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