Rotating Free Standing Mast Design

Discussion in 'Sailboats' started by Chuck Losness, Nov 14, 2010.

  1. Eunice Montjoy
    Joined: Nov 2010
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: australia

    Eunice Montjoy New Member

    Hello,
    Wooden Boathouse in Florida was building their 12', 14', and 16' wood-epoxy Prema dinghies, and they wanted to add rigs to each one. They all had to be of similar design style, and they also needed rudders and daggerboards. All they had to do was come up the road, and SYDI designed everything they needed--free-standing of course--in Cypress and Mahogany.

    Thanks
     
  2. Chuck Losness
    Joined: Apr 2008
    Posts: 350
    Likes: 48, Points: 28, Legacy Rep: 135
    Location: Central CA

    Chuck Losness Senior Member

    Eric,
    Thanks for your input. It is much appreciated. I just wish that Cat Ketches were more readily available on the used market with more to chose from then the older Freedom's. My opinions on why they didn't catch on are radically different from yours. I will share them with you in a private message if you'd like me to but don't want to do an open thread. Again thanks for all your input on cat ketches and free standing masts.
    Chuck
     
  3. Eric Sponberg
    Joined: Dec 2001
    Posts: 2,021
    Likes: 248, Points: 73, Legacy Rep: 2917
    Location: On board Corroboree

    Eric Sponberg Senior Member

    Chuck,

    I've heard all sorts of reasons for the lack of cat ketches and free-standing rigs, and in fact, since I have been posting on this forum, cat ketches are much more readily accepted than before. And this is not due to me, really, but to the fact that readers have indeed studied them objectively, I think, sailed them, and have discovered that they have a lot to offer in the way of sailing ability and cruising performance. Most other people not in the know still feel they "look funny".

    There are a number of other designs available on the used market, and the most common ones are the Herreshoff, Sparhawk, and Offshore cat ketches. Various sharpie designs also qualify.

    Eric
     
  4. JimConlin
    Joined: Sep 2004
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Wellesley, MA USA

    JimConlin New Member

    supplier of bearings

    Who might supply the bearings for one of the stub masts?
    I think Harken quit the rudder bearing business.
     
  5. RHough
    Joined: Nov 2005
    Posts: 1,792
    Likes: 61, Points: 0, Legacy Rep: 793
    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    We saw this one whilst sailing the Whitsundays

    [​IMG]

    Wylie 66
     
  6. troy2000
    Joined: Nov 2009
    Posts: 1,738
    Likes: 170, Points: 63, Legacy Rep: 2078
    Location: California

    troy2000 Senior Member

    Eric and Chuck, thanks for the answers on why one might prefer a stub mast -- even though it took me a few days to check back with this thread.
     
  7. Eric Sponberg
    Joined: Dec 2001
    Posts: 2,021
    Likes: 248, Points: 73, Legacy Rep: 2917
    Location: On board Corroboree

    Eric Sponberg Senior Member

    Hi Jim,

    In a very few words, not too many people. For one of my current projects, the GT80 sloop, we approached two well-known bearing manufacturers in Europe, and one declined, the other never answered emails promptly or with any helpful information. We decided to design and build our own--"our" meaning I will design, and the builder will sub out to a mast builder/machine shop to build the bearings. The bodies will be machined out of 6082 aluminum ingots because the mast builder does that all the time--they are very good at it. We will have to hard-anodize the aluminum and over-wrap the carbon fiber in fiberglass to isolate the bearings from the carbon. The rollers will be stainless steel.

    In researching that project, I came to the conclusion that cast silicon bronze bodies make a lot of sense--for strength and stiffness, for hardness, for corrosion resistance, and for galvanic resistance in relation to carbon. So I am advocating custom bronze bearings, again with stainless steel rolling elements (either balls or rollers) as the ideal way to make mast bearings. A good casting shop and machine shop could do a great job if they follow the plans properly. We are going to try to do this for the new Globetrotter 66.

    Eric
     
  8. idkfa
    Joined: Sep 2005
    Posts: 329
    Likes: 6, Points: 18, Legacy Rep: 79
    Location: Windward islands, Caribbean

    idkfa Senior Member

    standing a mast over a stub, even on a small boat, requires a crane?

    thks
     
  9. Eric Sponberg
    Joined: Dec 2001
    Posts: 2,021
    Likes: 248, Points: 73, Legacy Rep: 2917
    Location: On board Corroboree

    Eric Sponberg Senior Member

    Any kind of a boat over 28-30' is going to require a crane anyway to get a mast installed safely. On boats smaller than this, a stub mast may not make sense, and it just may be easier to make a one-piece mast with deck and heel bearings which one might be able to install with the equipment and people on board. You will likely not be going out in green water weather, or if you do, the amount of water that gets past the deck bearing my be easy enough to handle.

    The first time I used the stub mast concept was on Wobegone Daze, a Freedom 38, and I have not designed any masts since smaller than this. And not for lack of inquiries, but most people who ask for a wingmast on a small boat come to realize that the design fee is more than they want to spend on the whole mast, and most don't have the skills, equipment, or budget to build the mast in carbon fiber on their own. Getting into the smaller sizes, it usually becomes apparent that aluminum sections or a wood-epoxy mast will work pretty well, they are relatively inexpensive, and could be built by experienced do-it-yourselfers.

    Eric
     
    1 person likes this.
  10. petereng
    Joined: Jan 2008
    Posts: 581
    Likes: 22, Points: 28, Legacy Rep: 252
    Location: Gold Coast Australia

    petereng Senior Member

    Hi Eric,
    Have you considered Orkot type materials? They have similiar properties to bronze (their claim) They are usually cloth reinforced phenolic resin bearings. I have also infused PET cloth with epoxy to make custom bearings and they have worked quite well. As masts are slow moving roller type bearings are not required? I usually design spherical bearings for free standing masts to accommodate the mast bending. P{lain bearings can jam up under load? Cheers Peter s
     
  11. Eric Sponberg
    Joined: Dec 2001
    Posts: 2,021
    Likes: 248, Points: 73, Legacy Rep: 2917
    Location: On board Corroboree

    Eric Sponberg Senior Member

    Yes, I have used Orkot type materials for mast bearings, but usually in special situations where I know the turning power is pretty large--think balestron mast and boom. Generally, I prefer rolling elements and bodies all in hard metal so that friction is reduced to the minimum and so that there is no distortion of the rollers or balls. Masts really load up highly very quickly, and even when there is finger-touch smooth turning unloaded. When the load is on, it takes two really strong arms, or more, to turn the mast.

    Eric
     
  12. Eunice Montjoy
    Joined: Nov 2010
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: australia

    Eunice Montjoy New Member

    Hello,
    Wooden Boathouse in Florida was building their 12', 14', and 16' wood-epoxy Prema dinghies, and they wanted to add rigs to each one. They all had to be of similar design style, and they also needed rudders and daggerboards. All they had to do was come up the road, and SYDI designed everything they needed--free-standing of course--in Cypress and Mahogany.

    Thanks!
    ________________
    steel replacement windows
     
  13. brian eiland
    Joined: Jun 2002
    Posts: 5,067
    Likes: 216, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    How about a large diameter spherical bearing made of glass reinforced nylon?
     
  14. petereng
    Joined: Jan 2008
    Posts: 581
    Likes: 22, Points: 28, Legacy Rep: 252
    Location: Gold Coast Australia

    petereng Senior Member

    Hi Brian,
    Nylon is unsuitable for marine work due to its change in volume when it absorbs water (and dries out, gets wet etc). It can't be machined to the tolerance required for a bearing and then be expected to stay there. If it is machined dry then it will jam when it gets wet. The fibre reinforcing dosn't help either. Orcot is very good but pricy down here in Oz. Cheers Peter S
     

  15. cadmus
    Joined: Mar 2009
    Posts: 72
    Likes: 1, Points: 8, Legacy Rep: 10
    Location: USA

    cadmus da boom hit'um 1ce 2often

    the Righting Moment on Roll or Pitch Axis?

    Hate to bump a 2 year old thread, sorry. I read it ~2 years ago. I was going back to get the equation in this thread so I could play with some numbers and I noticed something.

    First of all I am a big proponent of stayless rotating masts and I love Eric’s stuff and his education efforts on many topics. I am not dissing the rig with these questions.

    When you say “righting moment” are you talking about axis along the length of the boat (roll)? These are less than righting motion of pitch. I doubt you were talking about pitch because that is huge but if predicting the max forces on a sail/mast that would be the axis to consider, not roll. So maybe you are talking about pitch righting moment (in which case i am very impressed but those spars).

    I find (qualitatively & anecdotaly) the largest forces on the mast when sailing to weather in large waves and swells. The boats seesaws and sometimes the bow repeatedly crashes and buries in. Obviously this is bad and uncomfortable but sometimes unavoidable, and sometimes unavoidable for long time frames. This is what i worry about in conventional and stayless masts. Not roll. Pitch is the axis that produces the strongest and most abrupt righting moment forces, right?

    I am trying to ensure that that the righting moment you use. OR that I am wrong and somehow roll causes more extreme and more fatiguing forces than pitch.

    For illustration of what I am trying to say, on a traditional rig if we put all rigging the same distance from the mast (same base of the triangles) the forestay and backstay would be seeing larger loads than the shrouds, right? Especially when we include the rapid changes in motion as we poound the bow down, seesaw or pitchpole. Not in smooth water conditions but in rough seas beating into wind.

    What is the righting moment of which you speak? The pitch axis: around the axis running from port to starboard. Or roll axis: the axis from bow to stern like we see denoted in hydrostatic stability curves.

    thanks,
    Pete
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.