Changing Catamaran Beams from Wood to Composite.

Discussion in 'Multihulls' started by Mark O Hara, Aug 4, 2020.

  1. Ad Hoc
    Joined: Oct 2008
    Posts: 6,609
    Likes: 617, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Overly complex and unecessary.

    You just need to account for stress - shear stress and deflection.
    That's it.

    Rather than throwing ideas hoping they stick... what is the displacement of your boat - full load... the CL to CL dimension...and the waterline length?
    It is much easier with numbers... than guess work.
     
  2. Mark O Hara
    Joined: May 2020
    Posts: 44
    Likes: 4, Points: 8
    Location: Mariveles, Bataan, Philippines

    Mark O Hara Junior Member

    Disp. – 11.5t CL to CL: 6.7m LWL :15.55m
     
    fallguy likes this.
  3. Ad Hoc
    Joined: Oct 2008
    Posts: 6,609
    Likes: 617, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Thanks.

    So..if you wanted to use the existing depth and width of the current/existing beams... what are these dims?
     
  4. Mark O Hara
    Joined: May 2020
    Posts: 44
    Likes: 4, Points: 8
    Location: Mariveles, Bataan, Philippines

    Mark O Hara Junior Member

    There are 6 beams in total not a straight line to be seen all bowed (see plan)

    Beams 1 & 6: 7.93m Depth: 0.166m

    Beams 2,3,4 & 5: 8.54m Depth: 0.203m


    Pahi Beam Drawing.jpg
     
  5. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,949
    Likes: 604, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    dearie me, whatever happened to simplicity ? It went AWOL with that boat.
     
  6. fallguy
    Joined: Dec 2016
    Posts: 3,339
    Likes: 439, Points: 93, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I am just a builder with no credential and only a little experience. Ad Hoc is the wise owl on your thread. You are lucky he coined in. The beam you have drawn up does not look good to me. I am not jumping on the bandwagon started by Mr E; this was my first thought.

    -Rather complex and the honeycomb serves little purpose that I see. Then I wondered..is the hourglass shape essential on the female side or to stop rotation somehow or aesthetics only?

    I would be more inclined to rethink that shape first, if it is feasible on the receiving side. Then the only purpose for the female mould is to get your cambers right which might be wasted effort to mould..

    ...by the way, Mr E was not wrong...I just didn't want you to think I am a bandwagoner...

    see what Ad Hoc says
     
  7. Mark O Hara
    Joined: May 2020
    Posts: 44
    Likes: 4, Points: 8
    Location: Mariveles, Bataan, Philippines

    Mark O Hara Junior Member

    Yes the recesses house the platform lugs which holds the deck. I chose honeycomb because of its compressive strength and it is needed. The beams hold up the deck-pods, the deck pods hold up the twin 17m masts that are yellow pine (Igem) and 225mm in diameter and weigh a bit. As previously stated I want to keep the shape, complex as it is, the same.

    Deck Detail 1.jpg Deck Detail2.jpg Pahi centredeck.JPG
     
  8. Alik
    Joined: Jul 2003
    Posts: 2,900
    Likes: 237, Points: 73, Legacy Rep: 1306
    Location: Thailand

    Alik Senior Member

    We did a study of CE-compliant P63 in composite recently. Not got to beams design yet. In general, composite will work, foam with UD and BX glass combination.

    On P63, those beam recesses in deck take a lot of accommodation space. What we did is we raised the whole thing up, did changes in hull shape, made better interiors. So strictly it will not be a P63, it is a replica boat which is now CE-compliant ;)
     

    Attached Files:

    bajansailor and fallguy like this.
  9. Mark O Hara
    Joined: May 2020
    Posts: 44
    Likes: 4, Points: 8
    Location: Mariveles, Bataan, Philippines

    Mark O Hara Junior Member

    WOW! That certainly is greater than 15%! Have you also omitted the traditional Wharram beam lashing system? If so how do you propose attaching the beams to the hulls? That certainly looks like a higher end cruiser. I originally built mine with the intent to do surf charter but with a young family now I just want to transport trade goods. I'm quite happy with the working boat finish.
    Is it possible to quote me for a laminating schedule for what I want?
    Laminating up in a mould taken from the original beams?
    Preferably Polyester GRP with a plain white gel-coat finish?
     
  10. Alik
    Joined: Jul 2003
    Posts: 2,900
    Likes: 237, Points: 73, Legacy Rep: 1306
    Location: Thailand

    Alik Senior Member

    Personally I don't like that lashing system and we have solution to avoid it. However, if Client for this boats wants it, can be done.
    Beams: You don't need to make them in mold; build base in foam and glass over. We can make a FEA study to finalize lamination schedule for the beams.
     
  11. Mark O Hara
    Joined: May 2020
    Posts: 44
    Likes: 4, Points: 8
    Location: Mariveles, Bataan, Philippines

    Mark O Hara Junior Member

    I was hoping by making them in a mould, finish first, it would be a lot faster and by-pass all that fairing and painting that has been done the first time. Also I don't like the finish on Flo-coat when its applied last, lot's of microscopic air bubbles, forever filling pin-holes. With regards to foam core we're very limited as to what we can get here, PU honeycomb no problem. How much is a Finite Element Analysis going to cost me?
     
  12. Alik
    Joined: Jul 2003
    Posts: 2,900
    Likes: 237, Points: 73, Legacy Rep: 1306
    Location: Thailand

    Alik Senior Member

    Drop me an email...
     
  13. Mark O Hara
    Joined: May 2020
    Posts: 44
    Likes: 4, Points: 8
    Location: Mariveles, Bataan, Philippines

    Mark O Hara Junior Member

    E-mail sent!
     
  14. catsketcher
    Joined: Mar 2006
    Posts: 1,298
    Likes: 143, Points: 63, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    The hourglass shape is pretty normal engineering - it is a modified I beam. I beams need really good web to flange adhesion so increasing the glue area where the shear web and flange attach is good engineering. It would also be pretty simple to build so it is good design in my books. Also Wharram boats almost never break and there have been lots built with huge builder variation. Wharram gets lots of feedback from hundreds of builders so the design has been through a lot of trial and error.
    After building boats in foam and glass and composite timber I would still go with composite timber. All of the pods and deck structure needs the beams to be exactly the same shape and removing the beam recesses would be a huge amount of work - the boat is 63ft and so I don't think interior volume is a problem. So changing the design is a huge amount of extra work.
    I would urge the builder to consider improving the timber used and glassing it. Cedar with unis top and bottom would be one possible start with a ply web or the same design with cedar flanges and uni top and bottom and a denser wood for the flange.
    Epoxy wood composite is very idiot proof. In Australia we have had a few modern beam cats and tris that used high spec mouldings to produce beams that failed spectacularly in early use. This design is proven, so I would caution deviating far from original when the only problem is a building issue. Rot can easily be stopped by total epoxy encapsulation - this is dead easy nowadays with composite fittings. It is not always a design fix, sometimes it is a construction or material issue.
     
    fallguy likes this.

  15. Mark O Hara
    Joined: May 2020
    Posts: 44
    Likes: 4, Points: 8
    Location: Mariveles, Bataan, Philippines

    Mark O Hara Junior Member

    Materials is a problem here, the material used was Red Lauan (a type of Philippine Mahogany) which is okay, other hardwoods are available locally are good for coffee tables but not for boat building. Plywood is inconsistent in quality, do a boil test on samples taken on different sheets using the same brand and you'll get different results. Some batches are good, some batches are terrible!
    Every time I go shopping I bring a Tramex Skipper-Pro non invasive moisture meter, and I don't buy anything with a moisture content of anything over 12%. Higher it is usually illegally logged and improperly seasoned.
    As I have previously stated Calantas (Philippine Cedar) would be ideal but I simply can't get it anymore. I know one person with a stock of it but refuses to part with it because of its scarcity.
    Yes Rot can easily be stopped by total epoxy encapsulation, but it doesn't stay that way, the beams move, a lot, one Pahi 63 owner reported as much as 150mm in 3m seas! And the worst place for wear is the lashing points which when move causes a chainsaw effect there the lashings bite into the protective coating, epoxy and furthermore the wood. Not only that the tripple braid lashings trap and hold lots of water, not a problem at sea but during the rainy season all that brine gets easily rinsed away and your problems start.
     
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.