Lowerable Mast on 40-45 foot yacht

Discussion in 'Sailboats' started by colinb, May 2, 2009.

  1. colinb
    Joined: May 2009
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    colinb Junior Member

    Hi all, I have a rather large problem, that will be a challenge to all!! I wish to buy a yacht 40-45 foot and moor it in our local waterway 200m from home. The problem is someone built a bridge with only 5 m clearance between the passage and the open ocean. Avoiding blowing up the bridge, does anyone have a concept for a lowerable mast (hydraulic), Telescopic mast and rigging etc, to solve this problem? Any help or tips would be appreciated. Of course I could always move to the other side of the bridge, but that would be to easy!!!!!!
     
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  2. Stutts
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    Stutts Junior Member

    A block and tackle system would probably not hack it. I think you would need a crane for sure!
     
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  3. colinb
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    colinb Junior Member

    block and tackle

    Thanks for your reply Stutts, I was thinking along the line a engineered pivot point just below the boom, with two large hydraulic rams, raising and lowering a free standing mast. The yacht engine could be fitted with a belt driven hydraulic pump, and the oil resevoir could be used to offset the balance caused by the hydraulic rams.

    I have spent my life working around large machinery, and believe the set up on large rotary blast hole drill rigs would be under more strain than the wind pressure on a large yacht sail. I need to start looking at wind pressures ratings on sails, masts, etc to get some idea of what I am dealing with.

    Any ideas or information would be appreciated. Would a free standing Aluminium mast be strong enough?

    Col
     
  4. MikeJohns
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    MikeJohns Senior Member

    You need a tabernacle arrangement and a sheerleg for lowering the masts. Often the anchor winch is used sometimes a dedicated cable winch just aft of the main mast or even attached to the tabernacle base itself.

    A robust tabernacle provides a moment connection and the hinge is usually level with the gallows that the mast will rest on aft.

    Alloy masts require some local reinforcement and a receiver for the pivot pin and for the lower locking pin but nothing particularly hard. The tabernacle and the support post need some thought but you don't usually need to modify the boat much at all.

    Heres a picture of a ketch lowering both masts in one operation, note the sheerleg.

    Cheers
     

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  5. Ramona
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    Ramona Senior Member

  6. colinb
    Joined: May 2009
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    colinb Junior Member

    Thankyou to Mike Johns, and Ramona for your feed back and photograph. It is wonderful to have so many helpful people around with great experience, and knowledge in the marine industry.

    I am over the moon that this idea is possible, and feasible, it brings yacht ownership (life long dream) a lot closer, as bearthing fees would make it very hard for us with a young family, mortgage etc.

    If anyone knows the contact details of someone who has done these alterations, or owned a yacht with these alterations that I may be able to speak to, I would really appreciate their contact details, or mine being forwarded to them.

    Col
     
  7. peter radclyffe
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    peter radclyffe Senior Member

    if your near melbourne contact richard blake, blakes boats
     
  8. capt vimes
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    capt vimes Senior Member

    there is a different and cheap option...

    A-frame rig.
    http://www.sail-the-difference.com/
    this is the link to a quite newly build cat with one of those masts.

    easily to bring the mast down without any additional winches/appendenges. easy to sail since you have no particular 'main'sail - no boom just 2 furlex 'fore'sails.
    very strong and stiff.
    will have some disadvantages as well.... but i don't know which those might be.
     
  9. colinb
    Joined: May 2009
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    colinb Junior Member

    Lowerable mast

    Thankyou Peter Radclyffe, and Capt Vimes. Thanks for all the information that has been posted to me to help. I feel I am now going in the right direction, however I believe a freestanding mast is the future in this situation to prevent damage and faliure to rigging. Unfortunately freestanding masts seem to have a stigma that no one wants to adopt at this stage. Can someone tell me why? There may be some really good reasons. I would be very interested in communuicating with anyone who has been directly involved in freestanding masts, particualarly if they believe this idea is possible. I really appreciate all feed back I get.

    Regards

    Col
     
  10. Steve W
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    Steve W Senior Member

    It seems that while maybe not impossible,it would be a lot more difficult to engineer a freestanding mast to raise and lower unassisted than a stayed rig.I have seen it done on some Bolger sharpies but the entire boat/rig package is designed one rather than as a retrofit.The Bolger advanced sharpie 39 is one example.
    Steve.
     
  11. peter radclyffe
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    peter radclyffe Senior Member

    the term freestanding is as you know different to stayed tabernacle mast, its usual in england to have big tabernacle masts on 80 ft thames barges, spritsail rigged, & 50 ft counter balanced wherry masts, similar to cat rig, mast in bow usually no jib, one halyard to mast , & one halyard for peak & throat, possibly unique, theres no problem with lowering masts but your gear needs to be well thought out & purchases set up for when your tired , on your own, not a gung ho bunch of monkey grinders who may not always be around, you can mock this all up on shore till its right, the sprit rig probably wont suit your boat, but the physics might, cutter, ketch or schooner, whatever, look at Gaff Rig by john leather , & norfolk wherry , & thames barge books, it is important that your mast is metal, or if timber has metal side plates fastened to the wood to provide a strong housing for the pivot pin, & preferablycomes up vertically against the fwd solid plate of the aft opening tabernacle, the stays & forestays, can have quick release, & handy billys, or come alongs, like backstay runners or boarding gates, but preferably you need a tapered fid steel to steel, at the back of the mast to lock the mast home, like a topmast fid, etc, like i say, for piece of mind, mock it all up on shore, you can fit a slave winch drum & snatch blocks where you like, back this all up with a manual winch , or tirfor cable winch,
     
  12. peter radclyffe
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    peter radclyffe Senior Member

    its usual to have 7/8th inch diameter of mast per ft of beam, colin archer has more lik 1 inch per ft of beam, you choose, the lower your rig ,the safer getting it up in a chop bear the sideways strains in mind so a taller tabernacle is better, & build it of 3/8 or 1/2 inch welded plate, something solid , its as important as your keel, & reinfoce solid to the keel with pillars, bulkheads, ringframes, whatever, it must not move, it must be as solid as a mast step, good luck
     
  13. Eric Sponberg
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    Eric Sponberg Senior Member

    Sponberg Yacht Design website


    Colin,

    Go to my website on the Free-standing mast page and you can read my article on the State of the Art of Free-standing Rigs. It will tell you most everything that you want to know about them, for example, why they are not as fully accepted as one might think:

    http://www.sponbergyachtdesign.com/StateoftheArt.htm

    A telescoping mast is practically impossible to make because in a stayed rig, the mast is in compression, and a telescoping structure cannot support compression easily. Note the operative word "practical" here. Yes, it might be possible to build, but not worth it because it just would not work well.

    In a free-standing rig, which is loaded sideways and behaves in bending, suffers different but just as complicated problems. The telescoping members have to be built such that in the raised position each one does not overload the rim of the member below. Close tolerances of fit are necessary, and that is always difficult to achieve AND carry load at the same time.

    In both situations, lots of parts are necessary to hold the mast parts together, and that is the practical problem to solve. Lots of parts means lots of cost and maintenance and also lots of sites for failures.

    The first solutions described above, tabernacled masts, are probably the most practical solutions.

    I hope that helps.

    Eric
     
  14. Timothy
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    Timothy Senior Member

    I am sorry to hear that a free standing telescoping mast is out of the question. I had thought that as two part windsurfing masts never fail at the sleeved joint that the mast section containing the buried portion of the mast section above it could be engineered to take the load, and that like free standing rotating masts only the the portions of the mast sections that are bearing on each other (in the case of the telescoping mast those portions of the mast sections in contact with each other when fully extended) need to be made with in close tolerances. I have been playing with a idea for a rig that reefing to a degree depends on the telescoping concept and am frankly disillusioned. Oh well back to the drawing board.
     

  15. peter radclyffe
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    peter radclyffe Senior Member

    in theory, it may be that we dont need standing rigging for any boat, but how big do the masts need to be, & is the windage the same as traditional rigging
     
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