Carbon Fiber Chainplates

Discussion in 'Fiberglass and Composite Boat Building' started by david@boatsmith, Feb 24, 2014.

  1. david@boatsmith
    Joined: Aug 2008
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    Location: Jupiter Fl USA

    david@boatsmith Senior Member

    We built some chainplates of carbon fiber for our new Ariki catamaran. We had some spools turned of 316 SS. These provided a nice saddle for the carbon to wrap around as well as a surface for the deadeye lanyards. This boat will have standing rigging of Dynex Dux from Colligo Marine. The bottom deadeye lanyards reeve right to the chainplate. We used 12" wide unidirectional tows. We wet them out folded them over and then passed them through holes in the deck. After splaying the tows out we vacuum bagged them to the inboard face of the daggerboard trunk. Then we capped the tows with a layer of 0-90 carbon fabric and a flange at the top. Nice!
    [​IMG]
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  2. david@boatsmith
    Joined: Aug 2008
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    Location: Jupiter Fl USA

    david@boatsmith Senior Member

    done
    [​IMG]
     
  3. michael pierzga
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    michael pierzga Senior Member

    I worry about the stainless thimble
     
  4. Eric Sponberg
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    Eric Sponberg Senior Member

    What's to worry about? David Halladay hired me to design these chainplates for Boatsmith, and I deliberately specified that the upper loops be lined with stainless steel liners. The stainless steel is for chafe because the rigging ends are lashed through these chainplates. Without the stainless steel liners, the rigging lashings would saw through the chainplates fairly quickly.

    Eric
     
  5. michael pierzga
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    michael pierzga Senior Member


    SS is needed for chafe. When ss is burried into the substrate it may create a moisture path. Id prefer to have the liner not burried into the deck
     
  6. Eric Sponberg
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    Eric Sponberg Senior Member

    The stainless steel is above deck only; it does not penetrate the deck laminate.

    Eric
     
  7. Steve W
    Joined: Jul 2004
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    Location: Duluth, Minnesota

    Steve W Senior Member

    Nice job David, that boat is looking great, a bit fancy for a Wharram though.This is a timely topic for me as im thinking about installing composite chainplates as a retrofit on a Gemini 3000 catamaran. I am installing the rig from a Gemini 3200 which is the next model of the same boat except the mast is located 27" further forward on a bulkhead and is 3ft taller and double in line spreaders so it has cap shrouds, intermediates and fwd and aft lowers. The caps, intermediates and fwd lowers go to 3 small ss chainplates grouped together on the bulkhead. the 3200 chainplates are off the shelf shaeffer straps 1 1/4" x 5/32" with a 3/8" pin hole with a 10" bury and bolted with 5 x 3/8" bolts. By my calculations the 3 chainplates together have a tensile strength of about 31000 psi. My plan is to use either e glass or s glass uni 4" wide wrapped through a slot in the deck and bulkhead 24" down and over a piece of ss tube above deck. For my application I don't see any reason to use carbon or even s glass really as by the time I duplicate the tensile strength it will still be fairly thin and as I will be using a hinged mast base and lowering the mast forward there will be loading in that direction as well as sailing loads so extra thickness of a lower strength fiber could be an advantage. Anyway, what im wondering is what safety factor should I use when calculating how many wraps of uni of whatever fiber I choose? I havnt figured out what they used when they designed the boat yet because im not sure of the shroud diameters, I need to measure them and compare to the chainplates, my gut feeling is that the chainplates are undersized as a few of these boats have broken them and even 3 x 1/4" shrouds would be 21000 lbs. I may or may not be able to vacuum bag these, well see.

    Steve.
     
  8. michael pierzga
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    michael pierzga Senior Member

    I see...no bury. i thought it was thimble shaped.

    For the scrapbook....An elegant chainplate for modern boats who use no turnbuckles and rig tension by mast jack.

    The oval shape allows shims to be fitted to correct any inaccuracy between port and stb standing rigging

    [​IMG]
     
  9. Eric Sponberg
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    Eric Sponberg Senior Member

    On David's Ariki catamaran I used a factor of safety of 5.0 over the strength of the shroud. You have to look at the geometry of the chainplate and decide what are the critical load paths, and determine if tensile strength or shear strength are the critical loads to follow.

    Generally, I am of the belief that if you think you need more than a factor of safety of 5.0 in anything, you probably don't have much confidence about the engineering problem and have to re-work your thinking so that you feel more confident in your work. This applies to any engineer.

    In this case, I knew I was not going to be in the plant to look over the work, and I did not have all of the details as to what care they were going to take, although I have a lot of confidence in David Halladay's work. I also knew this was going to be a wet lay-up of carbon fiber in a awkward, on-board situation, and so I adjusted my available laminate strengths accordingly, and used the FoS of 5.0 on top of that.

    I hope that helps.

    Eric
     
  10. Steve W
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    Steve W Senior Member

    Thanks Eric, that's what I was after. The load is mostly tensile, ie, it is a masthead, double spreader rig with in line spreaders so the caps and intermediates are pulling straight up although the fwd lower shroud will be pulling sideways some. Due to the location alongside a doorway I can not splay out the tows at all so they need to be just a 4" wide band but can extend a long way down the bulkhead. I just measured the shrouds this morning and the caps are 9/32" with the intermediate and lowers being 1/4" so it looks like the breaking strength combined is about 27000psi. Im not sure the best way to look at the existing chainplates, if i just consider the cross sectional area above the clevis pin hole which is 13/32" x 3/16" thick x 3 chainplates i get a number less than the shrouds, im not sure if this is the best way to evaluate them. Each chainplate is fastened to the bulkhead with 4 x 3/8 bolts with the cap and intermediates sharing the same bolts being one on each side of the bulkhead. The chainplates are 1 1/4" x 3/16". I think to achieve a fos of 5 i will need to use either s glass or carbon, i initially thought i could get away with e glass uni but i think it would get too bulky. What are your thoughts on making the parts off the job and inserting them through a slot in the deck and epoxying them to the bulkhead vs wrapping the uni through a slot in the bulkhead, the advantage is i would have better control over the quality of the part, i could infuse it which would be difficult in situ but wrapping it in situ means you are not just relying on surface bonding area.

    Steve.
     
  11. Eric Sponberg
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    Eric Sponberg Senior Member

    Steve, you can check an article on my website called "Engineering the Sailboat--Safety in Numbers" which was originally published in SAIL magazine in June 1985. Here is a link:

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

    Scroll about 3/4s the way down to the brief section on chainplates and the areas you should check, both in the chainplate itself, in the fastening bolts, and on the bulkhead to which it is attached.

    You used "psi" for units on your shroud strengths, which by my reconning should be "pounds". Be careful you are using the correct terminology. Also, by cutting slots in the bulkhead and wrapping glass through them, you are destroying the strength of the bulkhead. It would be better to use bolts again through the laminate, not a slotted wrap through slots.

    Is there some reason you don't want to use stainless steel again for the chainplates, although maybe thicker with a differently designed head for more strength? Why reinvent the wheel, so to speak?

    Eric
     
  12. Steve W
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    Steve W Senior Member

    Thanks Eric, im not commited to going the composite route yet, just exploring the option. What I had not mentioned is that along with installing the taller rig further forwards I plan on making it so it can be raised and lowered by hinging it forward, as you know, if you can get the pivot of the mast and the chainplates in line the mast remains well supported athwartships and on the Gemini this is a lot easier to achieve than on most monohulls, anyway I have to completely redesign the chainplate setup so i have the opportunity to make it stronger and build in some safety margin which does not exist with the original. I was going to fabricate everything in aluminum, i know,not a popular choice but it works fine and for this application better than stainless. I usually do all the fabrication myself but hire out the welding, then do the fettling and send out for anodizing, but it occurred to me that I could do the whole job in composites myself. I would have to disagree on the slotted bulkhead detail, it is a common way of doing this type of chainplate and as long as the slot is well down the b/head, in this case 24" i see no strength issue, no worse than a row of bolt holes further towards the top, the original chainplates had 5 x 3/8" bolts in the top 8" in line with one another. I cant splay out the uni on the b/head as there is no room and wouldn't want to rely on bonding alone on a plywood bulkhead anyway as all the bonding strength of epoxy is only as good as the first veneer, fine if it were going on a composite bulkhead. By doing the slot the entire thing is done in a continuous wrap to the required thickness and really does not depend on the bond at all although 192 in2 of epoxy faying surface is nothing to sneeze at. Everything is a compromise and I would be comfortable with this one. You can see an example of this method on an Orams cat on The Coastal Passage online magazine website. I looked at the link to your Pro Boat article, am I correct in thinking that the combined cross sectional area of the chainplate at each side of the clevis pin hole is the dimension I would use x the 3 straps, to calculate the strength required? if so it adds up to just marginally more than the breaking strength of the 3 stays so I would then multiply by 5 for the safety factor. This will determine what the choice of material. Your are right on the terminology, it should have been pounds.

    Steve.
     
  13. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    As a "general" rule this is ok.

    But it does depend upon the application,the client and of course the "assumed" quality of the finished item being made. The UK MoD for example require a FoS of 9 on all lifting devices.
     
  14. Steve W
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    Steve W Senior Member

    Is that for lifting devices in general or when lifting humans, that sounds rather excessive to me, where do you stop. My Gemini cat chainplates essentially have no safety factor and while some certainly have broken them I don't know of any that have lost a rig because of it, im not trying to justify this, it is clearly under designed but I would think that 3-5 should be adequate. When I was a boatbuilding apprentice 40 years ago we had a saying that went something like, an elephant is a mouse built to marine department specifications.

    Steve.
     

  15. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Can't quite recall now, it was a few years ago i did one. But, I think it was for all devices.

    Me too..but that's what their requirement was...they are the customer!
     
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