Lowerable Mast on 40-45 foot yacht

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

  1. rob denney
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    rob denney Senior Member

    G'day,

    Unstayed and telescoping is by no means out of the question. I have the engineering and plans for an 18m/60' telescoping mast for my 15m/50' harryproa, which I will be building in July. The purpose of this is to allow more sail to be carried in light air, not to get the mast low enough to go under bridges, but the principal is the same.

    I should have it working by the end of the year, happy to tell you all about it then.

    Info on my boat at http://www.harryproa.com/SoloTranspac/Solitarry1.htm Pictures of the rig on a proposed 12m/40' version at the bottom of http://www.harryproa.com/newsletter0608.htm

    Peter,

    Not just in theory, but in practice, we don't need rigging on masts. How big do they need to be? The mast on the boat in the video at http://www.youtube.com/watch?v=8chR6DAFjGA is 300mm/12" dia at the deck and tapers to 100mm/4" at the tip. It has far less windage than an equivalent stayed mast with all the wire and rigging. The mast weighs 120 kgs/260 pounds (about the same as an equivalent alloy mast with ss rigging), with a much lower centre of gravity.

    The boat has righting moment of 18 tonne metres/ 12,000 ft pounds, which is way higher than most monos of equivalent size.

    This mast is keel stepped, but we have built unstayed masts for Norwalk Island Sharpies that were tabernacle stepped and they worked well.

    regards,

    Rob
     
  2. Eric Sponberg
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    Eric Sponberg Senior Member

    Timothy,

    Telescoping masts and jointed two-part masts are different animals. Windsurfer masts, in comparison to larger sailboat masts, are pretty lightly loaded, and the joint survives OK. They also have wrap-around sails that you don't reef, so you don't have that problem on windsurfers.

    I don't specify wrap-around sails in my free-standing mast designs. They are difficult to cut, more expensive than single-ply sails, they are difficult to raise and lower because of the friction of the sail on the mast, and they are very difficult to reef well and hold their shape. In short, they are a lot of trouble. Freedom Yachts gave up on them over 25 years ago.

    Also, a wrap-around sail necessarily implies a round section mast, and a large-radius round leading edge on an mast is just not friendly to the air flow--the boundary layer separates earlier than it does otherwise on an elliptical leading edge. Windsurfer masts are round because they are easy and cheap to make. If they had elliptical masts, they would be better, but more expensive.

    So for a much larger sailboat, that leaves me with a mast and sail track on a tapered elliptical mast section for the best aerodynamics and ease of handling. So if I telescope the mast, how do I accommodate the sail track and line it up properly from section to section? Difficult to do, to say the least. The point here is that I can't do both at the same time. I would have to give up my aerodynamics and ease of handling for the telescoping feature.

    Rob, it will be interesting to see your results on your new telescoping mast, and I look forward to your reports.

    Eric
     
  3. rob denney
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    rob denney Senior Member

    I agree about wrap around sails, not sure I agree about the need for elliptical masts on windsurfers (and moths), both of which do pretty well with round masts, and have plenty of money, time and incentive for trying different ideas. Definitely agree on bigger masts though, which is part of the reason for a wing section on my boat. The other parts are there is less carbon in an unstayed wing than in a tube, the torque and alignment issues are easier to resolve and the wing can (theoretically, this is something else to test) double as a storm sail. There are also more options for sail shape with a rotating mast with more stiffness in one axis than the other.

    It is easy to get the aerodynamics and the track lined up if the top part of the mast is the outside of the telescope and you use slugs in a track rather than a bolt rope. Looks strange, but as a proa designer, I am used to this. ;-) There are a few other problems, but these won't be resolved until we have a full size rig to test.

    rob
     
  4. peter radclyffe
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    peter radclyffe Senior Member

    thanks
     
  5. colinb
    Joined: May 2009
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    colinb Junior Member

    Lowerable mast

    Hi to all, and once again a huge thanks for your wonderful replys. I see there are differing views on free standing masts, rigging, telescoping, etc. I guess we all tend towards what we know best. I'm luckier than all of you, I have no knowledge of any of them, so perhaps have a clearer view!!!!!!!!!! I feel visual effect has a part to play in this, so may have come up with a solution all round!!!

    Looking at all of the information that has come in, and visiting the local Marina last week looking at mast designs, I have come up with these questions for all to ponder.

    Would a free standing mast with forward and aft rigging added work? (forward allowing a head sail and aft for winching up, lowering down)

    Could it be lowered forward instead of backward like a tabernacle, using the boom as a sheer leg for a leverage point? (this allowing a furling head sail still)

    What would a free standing mast suitable to a 40-45 foot yacht weigh?

    Remember, this is to get under a bridge. If we can come up with a solution to this problem that is simple, reliable and not exceedingly expensive, we will make the world of yachting more affordable for a lot more people, in turn helping the industry as a whole.
     
  6. Eric Sponberg
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    Eric Sponberg Senior Member

    You can make the mast free-standing and add stays, that's not a problem. Using the stays changes the loading in the mast somewhat, so you just have to take that into account in the engineering of the mast section and wall thickness.

    There is no reason why you cannot lower the mast forward. You have to consider the mounting arrangement, however. With a single-piece mast (goes through the deck), if you are going to pivot it near the deck or gooseneck, you have to allow for movement of the lower end of the mast (under the deck) to pivot upward and through the deck as the mast tilts down. This necessarily demands dedicated space in the boat's interior and the deck design/structure for the lower end of the mast to pivot through. Most people will find this objectionable to their already limited interior space. Also, the trough collects water (rain, spray, waves, etc.) which has to be readily drained away. In all, it is an extra special feature that has to be dealt with.

    Conceivably, one could use one of my two-part mast designs, with a stub mast that goes through the deck and is fixed, and a wingmast that mounts onto that, and pivot only the wing part at the bearing at the top of the stub mast. I have never done this before, but it could probably be figured out. The wingmast actually rides on two bearings on the stub mast, one at deck level, the other at the top of the stub mast maybe 6-8' up. The upper bearing is made to allow the wingmast to pivot downward. So the lower end of the wingmast around the bottom bearing would have to be made to be disassembled, allowing it to disengage from the lower bearing. When back upright, the mast is reassembled and locked around the lower bearing so that it can handle the normal sailing loads.

    The two wingmasts that I designed for Wobegone Daze, a Freedom 38 cat ketch, each weighed about 260-280 lbs. The fixed free-standing mast that I designed for Copernicus, a Spencer 42 sloop, weighed about 595 lbs., and that was heavier than it should have been. Could have been maybe 100-150 lbs lighter. So for a 40-45' boat with one mast, I would expect something in the 400-500 lbs range for mast weight. More accurate weights can be figured with more detailed engineering, and that all depends on the righting moment of the boat and the height of the rig.

    I hope that helps.

    Eric
     
  7. brian eiland
    Joined: Jun 2002
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    brian eiland Senior Member

    Mast Lowering

    I might suggest you look thru these forums for all the postings by this fellow Stefano (Spiv). Here is his latest solution to the very same problem with a bridge. And this is not his first big vessel with a lowering mast.
    http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-8.html#post273502...posting #114

    Photo of his older vessel
    http://www.boatdesign.net/forums/multihulls/main-less-rig-21274-8.html#post252900

    To find his other postings, click on his name and visit 'all of his postings'.
    You might also visit his gallery of photos
    http://www.boatdesign.net/forums/profile/spiv.html
     
  8. brian eiland
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    brian eiland Senior Member

    This looks great in pictures, but notice the water is PERFECTLY calm. Even with calm water, a persons weight on the side deck would be enough to heel the monohull vessel over just enough to cause big problems with that tall mast(s) and the leverage they would impart to the pivoting mechanisum at the base of the mast.

    Then your thinking the side shroud would restrain this sideways tilt. Well remember this shroud would have to be under constant tension during the entire lowering procedure. This means it needs to have the same radius of movement of that of the mast (point of attachment same as center of rotation center of mast, etc, etc, etc. And things get even more 'strained as you reach the bottom of the lowering process.

    I've been thru this exercise when I was developing the system for our 26' tall mast on the Firefly trimaran. Not as easy as it looks
     
  9. brian eiland
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    brian eiland Senior Member

    I think you should have a talk with Stefano. He's looking at a very similiar size vessel, and he's 'downunder' as well
     
  10. ancient kayaker
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    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    What about the design of a camera tripod leg? Can it be adapted to a large telescopic mast? I'm thinking that the sections can be raised one at a time, the inner/upper sections before the lower ones, with a latch inside each section to lock it to the next lower section, the latches would disengage automatically as the section is lowered, and the raising mechanism, whatever it might be, would be at deck level.

    Another alternative might be a Gunter rig in a tabernacle, which would reduce the moment to be supported.

    I assume the bridge is somewhat inland where there is substantially flat water which eases the engineering a bit, but with open ocean on the other side of the bridge; that might complicate the engineering. I assume that most lowering masts are for inland waters only.
     
  11. yipster
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    yipster designer

  12. colinb
    Joined: May 2009
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    colinb Junior Member

    Hi all, I'm back.

    After more looking and less talking, I have met a few people who are very interested in this idea. I believe my next step is to start work on some practical trials in the backyard. I plan to pour some concrete with mounting lugs in my backyard, and attach a mast to it via a pivot point to run trials. Is there any commercial sponsors out there who are interested in supporting me on this endeavor, and making some money if it all pays off. Mr Sponberg, Rob Denney, this may not be your ideal, but may encourage people over time to your advanced thinking. I am genuine, and will be honest that this may take some time, and definetily some help. Does anyone have a tired mast suitable to a 45 foot yacht to donate? I am willing to share the spoils with those who help, and from my research, there is definetly a market. Yachties are prepared to pay extra for a mast and mooring, rather than $100,000 for a berth with ongoing fees.
     
  13. FAST FRED
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    FAST FRED Senior Member

    A working system is quite simple and 150+ years old. .

    A tabernakle steps on deck , and to control the rig while being lowered requires a sheer leg and loads of work.

    The Britt river system of a Lutchett is similar but far easier to use.

    The side legs of a tabernakle are carrier down to the KEEL.

    The deck in front of the mast is modified to have a hatch the width and length of the mast from the pivot pin to the keel.

    With a suitable amount of ballast in the mast , raising and lowering is almost effortless.

    If you wish a 5 year old to operate it simply install a geared flagpole raiser at the pivot.

    This is a large (2 or 3 ft ) diameter rack gear with a geared pinion and crank to take ant effort out of the drill.

    The Thames barges just had the lutchet and could lower the rig WHILE SAILING , to get under bridges, owner and kid as only crew.

    FF
     
  14. ancient kayaker
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    ancient kayaker aka Terry Haines

    Used to be able to rent sailing barges on the Norfolk Broads in UK, same orpblem, and the mast came down just before the bridge and went back up again in a trice, hardly slowed the boat at all. Can't remember the details but sounded similar.
     

  15. Pacey16
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    Pacey16 New Member

    Yes nothing new here, come to Perth you'll see plenty of big yachts with tabernacles. I have a 52ft Ben Lexcen with a big mast that can go under bridges, I have only done it once (in 35kts wind, not fun) but the previous crew did it regularly on the run.
    Use 2 spinnaker poles as leverage supported by U bolts in the deck either side of the mast, disconnect the forestay and attach halyard to ends of poles, jack the mast down a bit to slack off the cap shrouds, run a line from end of spinnaker poles through block fwd to a suitable winch (preferably electric),
    swing the boom to one side and lower.
    One problem if you have swept back spreaders is the caps go loose as you lower the mast, no problem if your tabernacle is strong and the water is flat.
    My previous yacht had a fairly flimsy aluminium tabernacle and that broke eventually.
    If you want photos of a strong tabernacle let me know.
     
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