Engineer wanted for preliminary scantlings

Discussion in 'Class Societies' started by Brentmctigue, Jun 16, 2020.

  1. Brentmctigue
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    Brentmctigue Junior Member

    Hi,
    We need some assistance with preliminary scantlings for a 6.4m displacement catamaran, to comply with either ISO 12215 or Loyds SSC. It’s for high end assessment of costs and does not need to be detailed. Duflex composite panels from ATL are our preferred supplier, however if you have similar material library that would suffice.

    We have lines drawings, AutoCAD model and Delftship model. Our budget is minimal. If interested please get back to us with costs.

    thanks
    Brent
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    What kind of assistance are you seeking?
     
  3. Brentmctigue
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    Brentmctigue Junior Member

    Ad Hoc
    Panel selection and reinforcing, so that I can get pricing from the supplier.
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    It is a small boat.. so why not just post the dimensions, frame spacing, stiffener spacing displacement etc... as it shouldn't take more than a few mins to run through a simple rule check for compliance, such as SSC rules or DNV-GL.
    A picture/dwg would help a lot too..
     
  5. Brentmctigue
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    Brentmctigue Junior Member

    Ad Hoc,
    Preliminary images and drawing attached. LOA 6.4
    LWL 6.1
    Beam 2.5
    Beam of one hull 0.72
    Bridgedeck 0.5 to underside
    1.5 high overall (+ windscreen)
    Max speed 10 knots
    Displacement @ DWL fully loaded 1.260
    Draft 0.4
    Lloyds classification Catamaran G1 Yacht
    Composite construction in glass over foam. Bulkheads at 620mm centers from aft.
    scarpa64_005.png

    If anyone would care to assist that would be greatly appreciated.
    cheers
    Brent
     

    Attached Files:

  6. Alik
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    Alik Senior Member

    'Lloyds classification Catamaran G1 Yacht' is not applicable to this craft... Lloyd's class for yachts is only intended for recreational craft (yachts) above 24m.
    In terms of weight, it will be way too heavy with Lloyds, because LR SSC has min sandwich skins laminate weight requirement and it will result thick skins. Duflex panels won't work with such think laminate.

    To perform calculations and give lamination schedule, one should know location of stiffeners, bulkheads, etc. Laminate of panel depends on size of panel. This means one should locate some stiffeners and bulkheads, and then perform calculations of structure including laminate of panels.

    In general, I think naval architect never touched this project - drawings are bow to left. Otherwise such questions would never arise.
     
    Last edited: Jun 16, 2020
  7. Brentmctigue
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    Brentmctigue Junior Member

    Thanks Alik.
    No not a naval architect. Just a plain old ordinary architect. Ill make sure to orientate now to the right in future. I do plan on getting a naval architect involved in due course. I want to ensure I can afford to build it first, and the engineering is beyond me.
     
  8. fallguy
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    fallguy Senior Member

    I think you are due a beer.

    what is the goal of the boat?

    she's a tad short if you ask me
     
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  9. Alik
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    Alik Senior Member

    We can do calcs to ISO, if You need... But again, this is matter of structural scheme and I am concerned You won't accept such budget for engineering.
    Usually ATL will give estimate for Duflex themselves, this will be enough for first estimates.
     
  10. fallguy
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    fallguy Senior Member

    I am a little nervous about weight forward. The capt n pax seats n helm .are very far forward.

    Something seems a bit off. No disrespect meant. I am building a catamaran and I rather like them. At the speeds planned, you won't have much pounding, but seats that far forward are typically hell rides.

    Even just another boat wake is not much fun there.

    If the intent is an aft cabin, I really think you need more length to get the crew back more to midship.
     
  11. rxcomposite
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    rxcomposite Senior Member

    If you plan to use Duflex composite board how are you going to bend it to hull shape? I looked at their site and it says it uses PVC or San core but did not mention the facings used. Since it is prefabricated, it is usable only for flat panels.

    Uhm, Ok. reading further, it says fibers of Eglass or carbon can be used as facings. That means there is some engineering to be done to arrive at the optimum thickness of facing and core used. That will be charged to the finished product.

    ISO and LR uses the same method of calculations and gives the same results or generally close to each other. Both can be used for preliminary sizing but LR is not usable for this size of boat as it defaults to minimum standards for big boats. The method of calculations can be used but definitely not for use as a Classed boat. ISO will do but unless you want it to have a CE certificate, it will be heavy. ISO defaults to 80% of material published strength if not supported by coupon test. Coupon test are very expensive.

    If it is not going to be classed or requires a CE certificate, LR or ISO method can be used for preliminary sizing.
     
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  12. Ad Hoc
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    Ad Hoc Naval Architect

    Aaahh.. in that case then, as already noted by several posters above, you'll need to provided more data on the materials you wish to use, otherwise, any analysis will use 'basic' sales supplied data and may well end up heavier than you expect.
    The dwgs in themselves are not sufficient ... you would need more of a structural layout dwg to provide guidance to anyone. If none exists, then the job starts to get bigger and bigger.... and not a simple rule compliance check.

    Indeed, all Class rule are not suitable for boats under 24m, they state that in their preamble.
    But doesn't mean you can't use them of course as many do, as we have done many times in the past. But you're at the extremes of the rule sensitivity and outside the parameters of the database, hence the results tend to be over sized for smaller boats. In which case, if it is a vessel built to Class, you just provide a technical argument why you feel the scantlings are too heavy. Easy enough.... but that is far removed from a simple... panel size check as noted from the outset.

    Also, as noted above, if you require a certificate, that also changes the situation, compared to something for yourself.

    The issues you face are either small or very big, depending upon the route you wish to take.
     
  13. Brentmctigue
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    Brentmctigue Junior Member

    Fallguy, Appreciate your comments. My constraints when I started out were for a 5 person cat that would fit in the driveway. I’m pushing the limits on both ends.


    Thank you to everyone. Looks like I have to some more homework to do.
    Cheers
    Brent
     
  14. fallguy
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    fallguy Senior Member

    It is an interesting plan. Why displacement and not semi-displacement?

    What power?

    I could be wrong on the helm location. But typically a helm that far forward would have large engines on the stern to offset. So, I would be a little nervous about centers of mass of say a couple of 200 pound men in the forward station and how the boat might react with power only required for 10 knots.

    I am curious what the ppi or kg/cm is for this boat. Probably can be calculated from the hydrostatics. I did not see it directly cited.
     

  15. Brentmctigue
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    Brentmctigue Junior Member

    It to be electric powered. So small kw engines but big batteries aft. Unsure of kg/cm. Is that cm of waterline area or overall? My first guesstimate on weight is around 855kg with people and gear 1550. It would be good to have scantlings to firm it up. I’ve taken your advice and started an 8m hull. The lines look so much better being stretched forward. Like a Grainger catamaran that’s had a little too much Christmas pudding. Resistance calcs are much better. Just need somewhere to put it.
     
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