trimaran removing centerboard

Discussion in 'Multihulls' started by ar99kid, Mar 12, 2013.

  1. ar99kid
    Joined: Nov 2012
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    ar99kid Junior Member

    hello
    i am a new owner of a telstar 26' trimaran that i bought as a project . now i am completely remake it and redesign all the interior space . this is intend to be a sail cruiser between adriatic , mediterranean and aegean sea islands , spending 10-15 days abroad for 4 people. the trimaran is 26 feet long and very narrow main hull with retractable centerboard in the pocket... from this point of view there i a lot of interior space sacrificed by the center board ! i am thinking allot to remove completely the centerboard its trunk ! because i am a new sailor i need as much advices as possible on this problem . how bad it is for my needs to sail without centerboard ? how bad is affected considering the there are 3 slim hulls in the water so i am thinking there shouldn't be much more leeway ... am i right ? am i wrong ?
    thanks for looking any help is much appreciated and please excuse my english i am located in romania...
     
  2. Corley
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    Corley epoxy coated

    I'd not remove the centreboard or centreboard case. I'm not familiar with how the telstar trimaran is constructed but normally the centreboard case is a structural element that also helps with mast compression loads.

    Assuming you could remove the centreboard case you would need to replace the centreboard with some other form of leeway resistance possibly daggerboards mounted in the floats. Some cruising trimarans have used LARS (low aspect Ratio keels) for leeway resistance with reasonable success.
     
  3. Gary Baigent
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    Gary Baigent Senior Member

    If you remove the centreboard and case, you'll have to fit (probably, don't know Telestar) a longer mast support from base to the keelson.
    But you MUST still have a board of some sort to compensate for the CB removal; otherwise you'll be going sideways when beating to windward - which will drive you insane with frustration. Since you're concerned about main hull interior space, the obvious place is in the floats. And doing this, you can make the float dagger boards asymmetric and gain even better performance than original; that is if the Telestar doesn't sail with all three hulls in water (which will probably be the case with your full crew, food and gear). If the latter is true, the daggers will have to be normal symmetric design.
    Here is an altered B24 with dagger foils in the floats, just behind the main beam connection. Yours could be straight or angled.
     

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  4. ar99kid
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    ar99kid Junior Member

    thanks corley !

    yes , indeed the mast support goes into the case , but i want to remake it also from a stainless steel polished pipe which will be much stronger than the original one . also will be some other mods in the plan for raising the strenght on the mast supporting parts.
    so your opinion is that i can get away with some "fins" on the amas ? i was also thinking about that ... removable ones for transport
     
  5. keysdisease
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    keysdisease Senior Member

    Norm Cross designed keels for Piver Trimarans, the one he designed for a Nimble would probably be about right for a 26 Telstar. I owned a Nimble in the olden days that had fins on the ama's. They didn't do squat for leeway prevention and when you would fly a hull the fin would break water and make you steer a zig zag course, not good at all.

    Steve
     
  6. ar99kid
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    ar99kid Junior Member

    thanks Gary and Steve

    i am not an expert in boats shape in the water ... so i ask which dagger boat design is better : a long one along the hull or a short one but deep in the water ? because i am also considering in making a fixed one , outer on the hull , let's say 3-5 feet long , but only 1/2-1 feet deep so i can still work my way out on trailering the boat ...

    this boat is pretty heavy like 1.6-1.8 tons ( weighted when i bought it ) and i didn't sail it but from my research it doesn't fly the side hulls ... so all the time in normal condition you have all 3 hulls in the water .
     
  7. Gary Baigent
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    Gary Baigent Senior Member

    aa99, There are no rules ... but here is an exception - you MUST get weight out of the boat, that is if you don't want to wallow along like a fat hog.
    Also the heavier a 26 foot boat is, the more dangerous it becomes.
    So do not overload, nor place lengths of polished pipe inside. A light wooden strut will do the job and even better is to make a box beam strut for mast compression.
    Just build your daggers so they slide up and down in a case - then you'll sail well and still be able to remove them for trailering the boat.
     
  8. ar99kid
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    ar99kid Junior Member

    yes Gary , that i was thinking of also ! the actual center board piece of wood is like 30kg , the case seems also like 20-30kg . my mast support is like 5 kg ... i am very experienced in fiber glass , carbon fiber , TIG welding aluminum and stainless steel so i am not afraid of any modification . i have a tuning performance workshop here , but NO boat experience :( so it doesn't mater how hard it is , how complicated it is , i can do it but i need to learn what design , shape etc is better :)
    i was even thinking doing the amas dagger boards in carbon fiber and leave them on all the time . i can laminate and cook carbon so they can get hard as steel , be light and also able to support the distributed weight of the boat if sitting on a beach on all 3 hulls...
    thank you very much for all the help ! i need to study more , but seems that there are some posibilities to take it off and have another solution. this is something good for me and my interior .
     
  9. teamvmg
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    teamvmg Senior Member

    the Telstar has an arched beam across the coachroof with and off-centre post to handle the compression of the mast. So, in this sense, the centerboard could be removeable.

    Trust me, you won't even be able to motor the thing in a straight line without the centerboard down - let alone sail it! some sort of board is needed, maybe in the floats.

    Which Telstar have you got? I had #22
     
  10. gonzo
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    gonzo Senior Member

    Centerboard trunks are often a structural member. Adding fins or boards to the amas will increase the bending force at the beams with a probable structural collapse.
     
  11. Richard Woods
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    Richard Woods Woods Designs

    There were three (at least) Telstar variants, the original, very small interior, a mark2 and the mark3 which had more room and an interior tray moulding. The last were built in 1980. Tony Smith of Gemini fame built them in a yard next to Derek Kelsalls. Paul Gelder, ex Yachting Monthly editor had one

    I suggest you check out forums in the UK and contact Mocra to find more owners apart from teamvmg

    If you do take the case out you will need to reinforce the hull bottom as I imagine the case added a lot of stiffness, essential when you beach the boat

    I would be wary of adding boards in the outriggers, there will be high side loads on the skin and you'll need extra bulkheads and local reinforcing. Probably you'll need to take the decks off for access

    Why not put a LAR keel on the main hull. Maybe 400mm deep, 2000 long

    It will add buoyancy and be lighter than the case/board. Ideally you want a high aspect ratio, ie deep and narrow. But ideally you also want shallow draft (not so important in the Med) so a long and shallow keel is better. Its also better when you dry out and walk to the front of the boat. You don't want it tipping onto the stem

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  12. Gary Baigent
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    Gary Baigent Senior Member

    I would be wary of long keels and the variations on the main hull because they are urine poor compromises, poor lift to drag because of their low aspect ratio which results in poor windward performance - and still a fixed keel to flop the tri over on its ear when drying out. Sort of like a motor sailer compared to a yacht; pathetic as a motorboat, near useless as a yacht.
    Since you are a skilled bloke, the area below the old CB case requires reinforcing; a stringer of high density foam or wood with glass/carbon box weave laminated over the filled in slot, will do the job. It is basic, straight forward and simple.
    And since you're going to be putting in some hours doing modifications and getting rid of the draggy slotted CB, might as well do a proper job: daggers and cases in floats. You won't regret it.
     
  13. ar99kid
    Joined: Nov 2012
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    ar99kid Junior Member

    after last night and all the info i have read and all the support here ( thank everyone for helping me !!!) and the fact i have cut away half of the inner deck and seems that with a few minor mods i can bare with the CB case after all , i am facing two options :
    1. leave the case in place , but cut away all that is in surplus and try to make wider the walk space and also deeper in the hull so i can stand across all the lenght of the boat. this will be on the right side... on the left side i also thiking to cut the molded floor and make some reinforcement from the CB case to the hull . another thing is ti cut it lower to the min possible level and make a sealed top with only one small hole or something like this for the rope to pull the board in or out ... this will also need to cut the board on the top but this won't sacriffice any of the water area when down ! please see the pic

    2 the second option is to cut away completely the CB case and remove it , glass the bottom , reinforce it where it is needed and have a simple , wider walk space . this one leads to other two options from the responds i get from you :
    a. one long LAR keel at the main hull bottom or two on the amas ! in this case where is the best position looking form the side of the boat ? close to the center or can i move them a bit to the stern , to the end of the hulls ?
    b. make two dagger boards in the amas with retracting mechanism ... reinforcing the amas hulls to accept this king of load .

    for better understanding i have put some pics also with the connection of the amas to the main hull so everybody can see how strong/weak they are ...

    thank you for looking !
     

    Attached Files:

  14. Gary Baigent
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    Gary Baigent Senior Member

    Lock Crowther's (marvelous) Buccaneer 24 had a dagger sort of like a cross with a centreboard, meaning it was set in the case, raked aft, and loaded from the interior (maybe there was a cover in cabin top for entry, have forgotten how it was done) a dagger but you closed the top of the case, halfway up the cabin height interior, with a canvas top, like closing a duffel bag; you tied strings and this kept the water (mostly) out of the cabin (although at high speed water thrashed around under the canvas).
    So what I'm suggesting is cut away near all your centreboard case, leaving enough slot for a dagger, toss your CB and build a simple dagger a la Crowther. That way you will really increase your interior space.
    Better still, build your case right through the cabin top and build a high aspect ratio daggerboard, which you load from cabin top. Your water leakage problems are now gone, cabin area larger (except for the tall, narrow case going to roof) - did I mention, much better windward performance?
     

  15. gonzo
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    gonzo Senior Member

    The problem is that the reinforcement or modification has to be done in the whole structure if you shift the boards from the center hull to the amas. It is not just a local reinforcement at the amas. Also, the behavior of the boat will change drastically. The board is the main pivot point when you are tacking, that will change outboard.
     
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