Tabernacle feasibility 65ft carbon mast

Discussion in 'Boat Design' started by ryanonthebeach, Sep 17, 2020.

  1. ryanonthebeach
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    ryanonthebeach Junior Member

    Hey all, would appreciate your opinions/experiences on this

    Since it's likely cheaper than replacing a bridge, I'm wondering what the feasibility of using a tabernacle to partially lower a 65 ft deck-stepped carbon mast (non-rotating) on a trimaran. Only stay forward is a single headstay.
    I've seen this used on smaller masts in Europe and assume the idea would scale up fine, but wondering if I'm missing something?
     
  2. bajansailor
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    bajansailor Marine Surveyor

    Is this a retro-fit on an existing boat, or a new construction?
    Re how the only stay forward is a single headstay, does she have a conventional arrangement with side stays and a back stay as well?

    It should be possible to build a tabernacle for lowering the mast - however I am thinking that for a 65' mast you would probably need a crane to lower it safely.
    I have sailed on a small yacht (24') which had a tabernacle stepped mast - she also had a pair of ally poles that were used as an 'A' Frame to lower the mast with - however her mast was considerably smaller!
     
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  3. gonzo
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    gonzo Senior Member

    You will need a jib-boom on the line you are using to control the mast with. Do you have a windlass or a reasonable size winch on the boat?
     
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  4. ryanonthebeach
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    ryanonthebeach Junior Member

    This would be retrofit on a 50- foot trimaran

    Gonzo, Yes a 1.5kw quick windlass and a pair of electric winches.
    figured I'd need a leaver arm out the front...
    I've seen some with a folding arm, that folds flat against the mast. It's attached with a hinge at the base of the mast, with the upper end, that would have a line to the windlass and to a tang attached somewhere further up the mast. So that it forms a triangle lever arm. They also used some system to that boom that allowed for attaching the roller furling over the line to slide it along with the mast so it doesn't unravel.
     
  5. gonzo
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    gonzo Senior Member

    If you have a spinnaker pole, it can work. It will need to have two lines going to the sides to keep it from twisting.
     
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  6. ryanonthebeach
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    ryanonthebeach Junior Member

    Thanks for the replies as always Gonzo, appreciate it. Stay safe
     
  7. Rumars
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    Rumars Senior Member

    As already said, it can be done but we need more details. Do you plan for this to be a regular occurrence or something you do once a season? Do you want to "shoot the bridge" or can you prepare the lowering beforehand? Roller furler on the jib?

    The basic system consists of a gin pole forward and a pair of shrouds in the same plane as the pivot point (they need to stay tight). From here on it depends on what you want and the existing setup.
    A real tabernacle is not required (and not indicated on an existing carbon mast) the maststep itself can be made to pivot.
     
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  8. peter radclyffe
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    peter radclyffe Senior Member

     
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  9. ryanonthebeach
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    ryanonthebeach Junior Member

    Now that's a fun bit of engineering! Thanks for posting
     
  10. bajansailor
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    bajansailor Marine Surveyor

    What a lovely film Peter, thanks for posting it.
    The Norfolk Wherry Albion does not appear to have an engine (?) - we see her tender helping to manoeuvre her, and a brief clip showing a crew member with I think a quant pole, but not using it.
    Quant pole - Wikipedia https://en.wikipedia.org/wiki/Quant_pole
    Later on there is a lad on a little yacht quanting her, and working up quite a sweat!

    These wherries used to carry cargo under sail, and they would literally 'shoot the bridges' - aim for the bridge, drop the sail, use the vessel's momentum to keep going, quickly drop the mast, and then hoist it immediately again on the other side.

    Here is another nice film showing a wherry under sail.



    I first came across Wherries and quant poles in the two books by Arthur Ransome about sailing on the Norfolk Broads about 100 years ago.
    These are Coot Club
    https://www.amazon.com/Coot-Swallows-Amazons-Arthur-Ransome/dp/1567925014/ref=sr_1_5
    and 'The Big Six'
    https://www.amazon.com/Coot-Swallows-Amazons-Arthur-Ransome/dp/1567925014/ref=sr_1_5
     
  11. ryanonthebeach
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    ryanonthebeach Junior Member

    Rumars
    You have a point, a hinge on the mast base seems far simpler as there are no major mods to the mast. Wont be able to lower it all the way with the bimini frame in the way but far enough for most bridges.

     

  12. Rumars
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    Rumars Senior Member

    Carbon masts are not usually engineered to be able to drive a big bolt trough them. If you want trunions it's best to glue them on and reinforce the area with additional laminate. The maststep is usually metal and you can weld on a hinge. If you want to use the spi pole as a gin pole please consult your mast manufacturer first about it to see if your carbon mast can take the resulting compression.
    As said one problem is the roller furler foil. You either have crew available to handle it while lowering or you leave it tensioned. To do that you permanently mount the furler on the gin pole.
     
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