Why the stainless fittings?

Discussion in 'Multihulls' started by catsketcher, Aug 21, 2012.

  1. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    Gday all

    I am in the throes of trying to get a good mast for my 7 metre folder. I have pretty strong views on being able to lift the thing. Some of you may remember my ideas on a sliding gunter but I am shying away from that now. I like the idea a lot but swaying up a 3 metre long gunter in a bit of wind could be a problem.

    So I have cut the mast down as much as I dare and got some quotes. I can get a good alloy kit for about $4000. The section is about $1000 - the rest is the kit. I can get a much lighter carbon tube for about $2500.

    So the carbon mast will be more because I will have to buy all the fittings but here is the rub. Why do people put T ball fittings on carbon masts? Surely I can make some nice unidirectional mast tangs, spreader fittings, sheave boxes, mast foot, tabernacle and gooseneck. Why would anyone ever want to bolt anything on a carbon tube? My folding mechanism uses unis to hold the hinges on and its great.

    I saw an idea where the Dux stay is wrapped around the mast under the attached sail track and held up by a protrusion on the other side. If I get a tube and do all the work before I glass the luff tube on then I can wrap unis around the tube to my hearts content. I have already used glass sheaves to handle my 38 footers jib sheets and glassed on shackles to handle the jib block too. I love it. Stainless and alloy are hard to work, cause stress concentrations, can corrode or leak and are heaps of money.

    So am I missing something cause it looks as though I could buy some uni and make my carbon rig for a fair bit cheaper than a kit alloy mast.

    Feedback please

    Phil
     
  2. redreuben
    Joined: Jan 2009
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    redreuben redreuben

    Phil I was curious about this too so emailed AES http://www.aes.net.nz/Rig Design Commentary.html
    and asked them.
    Here is the email and reply.

    Hi guys,

    Just a note to thank you for your webpages of very useful information, particularly the guidelines you offer for the homemade carbon masts.

    I have a question you may wish to add to your FAQs.

    If a builder wishes to build carbon parts to replace stainless steel fittings like tangs for shrouds etc would you use a similar strategy in that you stick with the original dimensions of the stainless piece ?
    I understand you may wish to vary the laminate to accommodate load paths etc but would the original dimensions be a good place to start ?

    Although I guess in a new build you feather the lay up into the surrounding structure could the above be used to replace existing stainless ?

    Cheers and Thanks,

    Hi,
    Thanks for email.
    Tricky one, I guess if each fitting were fully engineered then the final outcome would probably be much the same size and dimension as the stainless ones; so it looks like your suggestion would be close enough. But on any given fitting if you just ‘had a go’ without full engineering then some wrong fibre orientations could easily come back to bite you. Most times the fittings are such a small part of the total and can require so many hours of work, I would stay with s/s fittings and focus on making the biggest savings in the carbon of the mast tube.
    Chris

    Chris Mitchell
    APPLIED ENGINEERING

    M +34 666 255333
    P +64 9 889 3961
    S Chris_AES
    E chris.mitchell@aes.net.nz
    W www.aes.net.nz
    From: Reuben Filsell [mailto:filsell@myplace.net.au]
    Sent: Friday, 24 February 2012 3:31 a.m.
    To: "mailto:info"@aes.net.nz
    Subject: Carbon Masts et al
     
  3. Eric Sponberg
    Joined: Dec 2001
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    Eric Sponberg Senior Member

    Catsketcher,
    On the other hand, you can give it a go, but I would advocate for using carbon cloth layers, a mix of +/-45 and 0/90 layers rather than unidirectional only. Depending on the layup, you could put some UDR in there, but don't use it by itself--it could split later on. I attach an excerpt of a drawing that I did for a wingmast recently which shows and outside lug sitting atop a sheave box, and these are bonded into/onto the leading edge of the wingmast. The sheave box and lug are laminated with alternating layers of carbon fiber DB (+/-45) and Biax (0/90) fabrics to 16 mm thick. They are installed into the mast with epoxy glue, and then laminated over with more DB and Biax. Where the headstay attaches on the lug, there is a stainless steel bushing to take the bearing load of the headstay pin, which is nice and hard and will keep the lug from wearing out.

    I hope this gives you some encouragement.

    Eric
     

    Attached Files:

  4. cavalier mk2
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    cavalier mk2 Senior Member

    I noticed the sliding gunter showed up in Sail magazine on a "innovative" beach cruiser using much the same approach as I described. Done right the yard ascends veritically and doesn't flail about making reefing fast with a corresponding lower mast. While the yard can be lowered, for a beachcruiser I found it more convenient to brail the boom and sail vertically to get it out of the way.
     
  5. Red Dwarf
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    Red Dwarf Senior Member


    No way will original dimensions work as a starting point for carbon fittings. Carbon does not lend itself to small highly concentrated loads. It will take considerable expertise, engineering and testing to make fittings that can replace SS fittings.

    For example a balanced carbon laminate has around the same stiffness as aluminum. That is one third the stiffness of SS. In order to recover the stiffness you will have a very complex layup utilizing significant amounts of uni and intermediate modulus carbon fibers. Those fittings will cost a fortune.

    In auto racing with cost no object we wouldn't even consider replacing small highly/complex loaded parts with carbon. These small parts usually have very complex loading and the engineering of the laminate would be a nightmare and not save enough weight to be worthwhile.

    On the other hand carbon is perfect for large structures such as bulkheads and hulls and significant benefits will be found when switching to carbon.
     
  6. redreuben
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    redreuben redreuben

    Red Dwarf;
    I would have thought masthead fittings may be worth it due to the multiplication factor of being aloft ?
     
  7. Red Dwarf
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    Red Dwarf Senior Member

    That may work. Masthead fittings are fairly large and simply loaded. Are they usually aluminum?

    Do you have a picture of the part you wish to replace?
     
  8. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    I didn't explain myself very well

    On my boats I use unis wrapped around a composite tube to handle lots of tension loads - chainplates are an obvious example. You just lie the unis along the load path that the load would take.

    For mast tangs I would prefer not to have any tangs at all but to wrap the mast with Dux - much like the race boats do with their vangs.

    [​IMG]

    This would be done for the stays.

    I am not sure why a fractional trailer sailer with no backstay needs a masthead fitting so would go one sheave box up top. I have made sheave boxes by routing a corner on a piece of 19mm thick wood and taping over it. Then I put four layers of 440 db over the lot. I got a nice thin U shape section that holds Kankama's jib sheaves fine. They handle a 90 degree angle and I pull the sheet on pretty tight in a big breeze.

    For the gooseneck and mast pivot I would get some tube and glue to tube onto the section. Then I would get some carbon or glass tow and just tie the tube on with wet out tow. About 10 passes of heavy tow holds Kankama's jib leads on. This stuff is strong.

    So I can make my own sheave boxes that glue on, gooseneck and tabernacle that tie on with tow, spreaders would be cedar with glass on top that are glassed on, diamond attachments could be like the stays - wrapped around and then held in position with protrusions on other side. I could also tie on shackles with tow - that is what holds up Cats-paw's mast (chainplates) and Kankama's jib sheet return block. Really easy to make - get a handfull of tow, drape it over a large shackle, feed it through a hole and spread it out on the other side, cover with DB.

    I think to emulate stainless may be a heavier method than thinking like string. With such nice string - tow and Dux - we may be able to redo our masts - our decks are very different now - no stainless chainplates, stanshion bases etc.

    I will give it a go and see how it goes.

    Phil
     
  9. gypsy28
    Joined: Mar 2010
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    gypsy28 Senior Member

    Hi Phil, it sounds like an interesting modern way to fit out a rig, is it possible to see some photos of some parts you've already made?

    cheers DAVE
     
  10. catsketcher
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    catsketcher Senior Member

    I just got a new quote on the carbon section which was much more than I thought it would be - may be holding out and go with an alloy section then.

    As for tying stuff on with unis

    The first pic is my tied on motor pod hinge. All that keeps the thing onto the bridgedeck bottom is about 6mm of uni tow wound through and through the bridgedeck. Works well, no cracking and stands up to the force from a 25hp four stroke no worries.

    http://s1220.photobucket.com/albums/dd450/catsketcher/?action=view&current=DSCF1015.jpg

    The second pic is of my genoa sheet over sheave. The sheet leads over the cabin and down to the winch. I made this by rounding off the corners on some timber, taping over it with packing tape and glassing it over with about 4 layers of glass. Works well.

    http://s1220.photobucket.com/albums/dd450/catsketcher/?action=view&current=DSCF1017.jpg

    The genoa sheet then leads down to another pulley. Rather than go to the hassle of a proper chainplate I just put uni over the shackle and fed it into the hole. I then splayed the ends out about 300mm inside.

    http://s1220.photobucket.com/albums/dd450/catsketcher/?action=view&current=DSCF1018.jpg

    http://s1220.photobucket.com/albums/dd450/catsketcher/?action=view&current=DSCF1019.jpg

    My jib tracks are held on by tow too. I don't use tracks as they are pricey, heavy and leak and you don't move them once you get the lead in a good spot (I do move the lead outboard on reaches)

    http://s1220.photobucket.com/albums/dd450/catsketcher/?action=view&current=DSCF1020.jpg

    You can barely see the lump in the floor for the motor nacelle hinge

    http://s1220.photobucket.com/albums/dd450/catsketcher/?action=view&current=DSCF1023.jpg

    So you can see why I would like to do the same on a carbon mast. Shame the new quote is about a grand more than first talks described.

    cheers

    Phil
     

  11. gypsy28
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    gypsy28 Senior Member

    Thanks for the pics Phil, there are some pretty cool solutions you have come up with there, very custom and unique, and no leaks (gotta love that)

    The built in shackle is a pretty nifty idea, how do you engineer the laminates? or is it just a matter of make it over strong?

    Its got me thinking that in this day of composites you can just about get rid of all bolted on hardware !

    Bummer about the Carbon tube price, exxey stuff

    cheers DAVE
     
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