GRP Transom design for Sterndrive

Discussion in 'Boat Design' started by ToMeK, Jul 12, 2021.

  1. ToMeK
    Joined: Nov 2006
    Posts: 41
    Likes: 2, Points: 8, Legacy Rep: 10
    Location: Zagreb, Croatia, Europe

    ToMeK Young naval architect

    Dear everyone,

    Recently I got a bit stuck with one structural design problem. It is how to properly design nad analyse transom that carries 2 x sterdrives (engines 2 x 450 HP). It is clear what kind of forces and moments act on transom, but it still remains open how to analyse this problem. Also, according to some recommendations I plan to use GRP sandwich with 30mm plywood as core.
    Hull is around 12m long GRP sandwich (with SS keel and chines). Structural liner is used to support bottom in engine room. Brackets are used to transfer load from transom to longitudinals.
    I was looking for some rules to back me up, but besides ISO that covers engine Ptot up to 100 kW there are no other guidelines.

    FEM is one option but, I am looking if there are any simpler methods to analyse this problem.

    Please help :)

  2. Alik
    Joined: Jul 2003
    Posts: 3,062
    Likes: 348, Points: 93, Legacy Rep: 1306
    Location: Thailand

    Alik Senior Member

    We use FEA for such problems.
    Other option - just build from experience.
    Dave Gerr and other authors give some recommendations for transom reinforcements in books.
  3. Ad Hoc
    Joined: Oct 2008
    Posts: 7,698
    Likes: 1,570, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Hi Tom,

    It is much easier than you realise.

    All you do, is place the stern drives where you need them, then first of all draw the supporting structure you need for them and blend them back into the existing structure.
    Since you know the forces/loads, you can now identify the load paths - the load paths are the key to all structural design problems.

    Once you have that, for each structural member it then becomes a simple check of:
    i) bending stress
    ii) shear stress
    iii) defection
    iv) fatigue

    And that's it.

  4. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,390
    Likes: 1,039, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    The SS chines sounds different
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.