composite davit design

Discussion in 'Sailboats' started by ABD, Mar 26, 2018.

  1. ABD
    Joined: Feb 2018
    Posts: 6
    Likes: 0, Points: 1
    Location: Argentina

    ABD Junior Member

    Hello everyone, I am designing a pair of composite davits and i am looking for some validation on the design.

    The davits are intended to carry the following weights

    -Dinghy (empty) = 77 Kg

    -Engine (15 HP) = 59 Kg

    -Fuel tank = 21 Kg

    This gave me a total of 157 Kg. To this I added the possible weight of water as a 80% of the boat inner volume ( L=2,67 m B=0,84m T=0,4 m V =0,9 m3) giving me a weight of 735 Kg. Finally I accounted the dynamics loads as 1,5 x Total weight = 1338,65 N, so in each davit I will have a load of 670 N.

    The davit will have a box section (h=140 mm b=200 m) and distance from the pivoting point to the applied force 1,5 m. The most compromise section will have an axial load of 2,95 MPa.

    I plan on doing a lamination schedule mostly on the longitudinal direction (0º) to stand the tensions caused by the moments, some 45º to account for possibles side forces and some 90º to withstand the vertical forces (shear stresses = 0,68 MPa). The laminate will have a thickness of 10,38 mm

    I obtained the laminate moduli and the strains. With that i was able to obtain the tensions in each of the plies and verify against the TSAI-HILL criteria and ultimate stress. I also checked for buckling of the panels and shear and so far so good. My problem is to check for vertical deflection. I did it using the following equation:

    deflection=P(L^3)/EI + PL/GA

    where E = Ex of the laminate and G = Gxy of the laminate. Which gave me an 3,4 mm deflection. I think it may be to little so I am not sure if this is correct. Any thoughts??
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