Engineer wanted for preliminary scantlings

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

  1. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    I built in a female jig with tortured panels. It was fun.

    walk in and out, hulls were a bit wider, but bottom was 20" only

    I might have built a nosecone instead next time; the bow work was a bit tight.
  2. rxcomposite
    Joined: Jan 2005
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    Location: Philippines

    rxcomposite Senior Member

    Of course you can always achieve 10 knots with lots of power. Just don't punish your propulsion equipment by burdening it with too much resistance.

    You can lengthen the hull as others have suggested. 8 to 8.5 meter seems to be a sweet spot. Length is always beneficial. Try to design at cruising speed of 6 to 7 knots, 9 to 10 max. Your Length to Displacement ratio should be around 9 to 10.5 in order to be a high speed/ light displacement craft. Cannot be a displacement craft form.

    At that Froude number, you need a high speed semi-displacement hull form. The midship coefficient you have suggest an elliptical hull or a deep V. Try a parabolic and higher midship coefficient. You Cb is also low at 0.408. Ideal would be in 0.48 to 0.52, typical of frigates and corvettes. If you look at modern AC hulls, you will see the same section except that the hulls are much slimmer because it is a cat. Low entrance angle also.

    LCB of these hulls tend to be aft, around -2 to -2.25% so check your configuration. Bowrider might not work.

    I am still at the early design analysis, I try to fit the ratios and coefficient around the design lane. In the final stage, I work around the same principle of Michlet. I create a "family" of hulls that fits the design goal, then choose. That way, I don't feed the program with random numbers that I just think of.
    fallguy likes this.
  3. rxcomposite
    Joined: Jan 2005
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    Location: Philippines

    rxcomposite Senior Member

    Agree with Alik. You can always build a birdcage mold, screw from inside the foam planks to follow shape, sand the joints, glass one side, remove screws, invert to a cradle and glass inner side. You can use heat gun if the foam is a little hesitant. Wear a mask. The fumes/outgassing is toxic.

  4. Brentmctigue
    Joined: Apr 2015
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    Location: Newcastle

    Brentmctigue Junior Member

    Looking into foam in lieu of Duflex. Watched a few videos and it looks easy enough.
    Ive had another go at the boat design. Appreciate all your input. Ill post it in the boat design section.
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