Composite Rudder Part Design

Discussion in 'Boat Design' started by ryanonthebeach, May 20, 2015.

  1. ryanonthebeach
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    ryanonthebeach Junior Member

    Guys... some composite advice or pointers to good sources of info would be appreciated.

    Have to rebuild some of the wooden parts that connect the rudders on a catamaran to the crossbar. (pictured) Cat is 27 ft heavenly twins. I have some corecel 1 in (5lb density), Fiberglas and some left over carbon fiber.
    Attached pictures to show how the wood split (note that I covered it in a thin layer of glass last season.... mostly cause I was practicing vacuum bagging techniques and because I was tired of varnishing. )
    These parts split because the boat was grounded in a lagoon for the winter and at high tied in a nor'easter it did some significant slamming (not at all usual treatment)

    [​IMG]
    image doesnt seem to work so here's a link wood part

    Couple of questions

    1. Can I make a sandwich part as strong (or close too) as wood with the above materials? (skeptical) I've cut the foam and it seems soooo light by comparison. Not sure of the type of wood think it was mahogany or one of the harder lighter color woods, but not teak. Can make it thicker to achieve more strength.... currently 2in x 2in
    2. If one is close enough, is there a guide / formulas / rule of thumb out there on how many layers, type, weight, of fiber to use for what strength over a certain thickness



    Thanks!!!
     
  2. rowen01960
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    rowen01960 Junior Member

    Do you wish to repair the wood parts for short or long term use? Or do you wish to replace the damaged parts for long term use?
    If you provide dimensional sketchs with attachment hole locationsdiameters .. I can work up a laminate scheme for repair or replacement. The 5# core will suffice for the beam sextion but not for the local attachment points ...
     
  3. ryanonthebeach
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    ryanonthebeach Junior Member

    Thanks for the reply Rowen. This is for long term use.
    Here's a link to a sketchup of the part... dimensions are 2X2X18 with 1/2 in holes (diameter)

    [​IMG] Image link

    The three wholes bolt to the rudder and the one to the crossbar (there are two of these one for each side)
    your help is much appreciated... I can be flexible on the width etc.

    Adding some thought into the design.. thinking it may be good to widen the part across the length (as pictured) the stress on the part is side to side, little to no stress up and down.

    I've marked where the grain is and you can see how the cracks appeared the length of the wood, vertically.... may have been different if the grain was horizontal.
     
  4. ryanonthebeach
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    ryanonthebeach Junior Member

    Think I'm going to try this with some variation of that design ... maybe make the part shorter and put some extra reinforcement around the bolt hole areas. Maybe a few layers of unidirectional fibers running accross
     
  5. rowen01960
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    rowen01960 Junior Member

    Sorry for the delAyed response ... Too many aliigators around here :)
    I will run a series of schemes using the5# core with dominate glass reinforcement. The part is one of2 "Tillers" ? If the teleflex is still being used I will limit the tiebar tiller loading to 1KN at 3.5% I should have something to discuss Sat/Sun ... do not through out the old tiller ... You may need to use good sxn araes for bearing bushings ...
     
  6. ryanonthebeach
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    ryanonthebeach Junior Member

    oh... I think it's a much simpler set up than you imagine ;).... it's a very crude rudder control design. Basically the rudders (catamaran) are joined by a cross "bar" (more like a long plank) with these two linkages (the part in question) that link the cross bar to each rudder directly, no fancy stuff here, just thru bolts with washers to the rudder and to the cross bar. The bar is moved side to side by a single hydraulic ram that's connected directly (thru bolt) to the cross bar this has a bearing tiebar end and is able to move, the only part that flexes in fact. Since the rudders aren't entirely vertical there is some play with the bar but that's handled by the flexible ends of the ram.

    If this dons't makes sense I'll draw it up.
     
  7. rowen01960
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    rowen01960 Junior Member

    Ryan... I will shortly post a dropbox link for my weekend doodles
     
  8. rowen01960
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    rowen01960 Junior Member

    HT27Composite Tiller c1

    2 fullscale templatable drawings (pdf)
    1 powerpoint description/FEA results (pdf)
     
  9. rowen01960
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    rowen01960 Junior Member

    c1 Data Files

    Drawings Only for this message
     

    Attached Files:

  10. rowen01960
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    rowen01960 Junior Member

  11. rowen01960
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    rowen01960 Junior Member

    c2 Tiller Arm Design

    I have defined a second geomteric beam with lower weight and materials consumption, but it requires a more complex intercostal shape ... More hand sanding of the core. It would also benefit greatly with a proto (waxed wooden) mould. This would be preferred but only if the actual tie-bar were upgraded as well. Please note that if additional area is added to the rudder the ram, tie-bar tiller arm and Rudder mount should be reviewed for the additional loads being reacted ...i owe you the ply countour templates for next weekend ...need to return to billblework this week ... :) rob
     
  12. ryanonthebeach
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    ryanonthebeach Junior Member

    Wow, that totally blew me away, didn't expect such a professional workup. Seriously appreciated Rob!!!!
    This is really cool stuff. got to figure out how to do this one day.
    Going to take me a little while to process this... so far it's making sense.



     

  13. rowen01960
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    rowen01960 Junior Member

    Things to consider..

    Ryan ... It was my pleasure to illustrate a bit of what you should expect ... :)
    The original wood tiller was fine but for a finite period of use. The lagoon perio accelerated things, as will an increasein rudder area .... Seriously you need to consider the steering system as a whole if you increase actuated area!
    You can also play with the intercostal and bearingblock shapes ... Bond the 3 together (NO SQUARE ENDS) and measure the deflection of the Tie-Bar end with max 10-20# you should see no more than 20mm vertical displacement in order for a 3mm laminate to do its job for e6 life. The hydraulic ram should be limited to less than 1000#. The ply splice/stagger position is criticl dor bearing and flexural strength ... So practice the joint procedure with the objective of having less than 10% total CPT thickness varation across and along the Splice CL. Shearing (weave deformation) will be inevitable ... Just try to limit it to the marked zones. I should have c2 ready for next week ... It is starting to look at little like my old EC135 Flexbeam ... Not really surprising after all these years :)
     
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