Carbon beam

Discussion in 'Fiberglass and Composite Boat Building' started by fallguy, Sep 30, 2022.

  1. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I want to change the netting beam on my boat from aluminum to carbon. I want to modify the supports to carbon as well. I'd like to engineer a bridle attachment point to the supports as well and engineer a carbon backer. Boat is foam sandwich. M200 Gurit is the foam at the support.

    The existing tube is about 142" long, so the length of the raw tube needs to be 144".

    The existing tube is 44 pounds and I want to lose as much of that beast as I can. The netting beam supports a trampoline and should be rated for say 6 people or maybe 8 people plus safety factor. If we can shed 30 pounds up there; that is big. The trampoline is about 37" for an aft only and about 11" wide and is just an expedition webbed trampoline..

    In addition to a spec, I need some idea how to build the tube. I have vacuum.

    The tube does not have to be round, but would be nice if people can dangle their legs over it.

    Glad to pay for design and build instructions.

    I did call a carbon tube builder, so if I can find off the shelf; that'd be great. This tube is 4.5" od and the wall is about 1/4", so 3.7#/ft. It was anodized..

    399F5141-B638-4A79-8D00-4ED8160C56A0.jpeg
     
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    When are you planning on launching your lovely cat Dan?
    I am thinking it could be worthwhile just waiting until you have launched and carried out some trials before removing this beam and it's end supports.
    You might well find that you are happy with how it is? It seems like a lot of work in order to save about 30 lbs.

    What did you decide on for your anchoring arrangement - does the anchor live in the anchor locker on the bridgedeck and you lift it out each time you want to use it, or is it permanently mounted on a roller on the cross beam (or on the bridgedeck)?

    Re attachment points for the bridle for the anchor cable, are the S/S eye bolts in the stem (as shown in the photo) not strong enough for this purpose?
    If not, what is their function?
     
    Last edited: Sep 30, 2022
  3. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    Am I reading this right?You are trying to save a few pounds so that the weight of several people can be applied there?In percentage terms,the weight of the beam will become quite insignificant with people in place.The cost and the challenge of moulding a carbon beam are a real factor and I'd be curious to know what the metal socket is made from and how much electrical potential it has relative to carbon.There is also the factor that for best use of the properties of carbon you will need to be aware of fibre orientation or accept carrying a bit of extra weight if a less optimised layup is chosen.For surface finish and fewer severed or abraded fibres you would be looking at female moulding but for ease of construction,a male former is easier but has to be removed-leading to considerations of draft and then the subsequent finishing work.Is the gain really worth that amount of work?

    Many of the commercially available tubes are pre-preg and created on a CNC filament winding machine and then ground to a finished size before receiving a coat of lacquer to make them pretty.They won't have identical properties to a beam designed for your specific application.Without testing to determine their suitability for long term use in an exposed location it may well be possible that they will absorb moisture and wipe out some of the theoretical weight loss.I have no idea where you might get accurate information on this aspect.There are numerous youtube videos showing the process of making them.
     
  4. fallguy
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    fallguy Senior Member

    My boat has been launched and is 5" below her designed waterline at the bow.

    Please do not make inferences about things. I need to get COM further back. This is one piece of the puzzle. My cabin was a bit overbuilt. I am trying to shed all excess weight on the front and shift engines back 4". Please, if you cannot spec or answer how to build the tube....do not..
     
  5. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Dan, if we look at it another way, I think that even if you remove the whole beam entirely, it is not going to make much difference to the vessel's trim.
    And certainly a weight saving of 30 lbs will make even less difference.
    If it did, then your weight on the bow when anchoring would create a lot of bow down trim.
    I did not cotton on that she is now afloat - have you measured the bow down trim when you are standing up at the forward end (or maybe sitting on the cross beam, on the centreline)?
     
  6. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    Hallo Dan,
    a couple in Germany is building a 40' tri and made carbon tubes (for masts etc.). Sandwich structure with hard foam elements. Trials were made with glass. Aluminum core to give shape, stripped out after tempering.
    boote-forum.de - Das Forum rund um Boote https://www.boote-forum.de/showthread.php?p=4749574&#post4749574
    boote-forum.de - Das Forum rund um Boote https://www.boote-forum.de/showthread.php?p=4752117&#post4752117
    boote-forum.de - Das Forum rund um Boote https://www.boote-forum.de/showthread.php?p=5270377&#post5270377
    I don't know if it helps, but may be you will find some hints.
     
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  7. fallguy
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    fallguy Senior Member

    Not an issue underway. The boat is bow down at static rest. The cockpit and cabin are not level. The bows are axe bows and so the boat is very weight sensitive forward, and I need to make all possible modifications to move the com back.

    Modifying a 50-55 pound weight (beam) that is 1' from the end of the bow will probably allow me to keep an anchor on the pulpit. My anchor is aluminum and currently in the back of the boat.

    Otherwise, I'll need to modify the hulls. Underway, the boat is behaving pretty decent, made 20 kts today. Need to determine some excess splash issues. D3579021-826C-4536-A3C1-CB317D540B4C.jpeg
     
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  8. fallguy
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    fallguy Senior Member

    Sorry @wet feet .

    I want to make everything light as can be forward and move center of mass further aft.

    This is not to shave 40 pounds for nothing. This is a 50-55 pound (with fixtures that are stainless) moment I want to eliminate. The boat is a cat and weight sensitive forward,

    Solar panels were removed today. I may add one back in a further aft location.
     
  9. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    I would suggest adding a bow extension - a bulbous bow effectively.
    That's what I recommended HERE...and shown here in all its glory too.

    Solves 2 problems at once.
     
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  10. fallguy
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    fallguy Senior Member

    Gonna need to find someone to help me do that. Boat is coming out October 24.

    It runs great. Anyone know what causes the shower? Is that the jackplate or trim? I built the transom at 14 degrees, not 12. I did NOT try to trim up, but will next outing.

    https://youtube.com/shorts/udvt35fGLyg?feature=share
     
  11. redreuben
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    redreuben redreuben

  12. wet feet
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    wet feet Senior Member

    Ad Hoc makes a very good suggestion,by adding bulbs you will be compensating for the excess weight with additional carrying capacity.It is far from unknown for catamaran hulls to have them. Did the design include a note on any drawings giving the MCT? That would be useful information.

    Any beam you substitute could feature a dolphin striker if it shows too much flexibility.
     
  13. fallguy
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    fallguy Senior Member

    sorry, dolphin striker?
     
  14. fallguy
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    fallguy Senior Member

    This tensioner...how is it connected to said beam? 461196FD-EF09-4383-B829-A77762D02532.jpeg
     

  15. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    You could add a metal socket or mould a carbon version, its similar to a spreader but rotated vertical so something that works like a spreader bracket is the aim.
     
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