Bertram 20 Main chine hight at transom

Discussion in 'Boat Design' started by bigjonny9, Aug 25, 2019.

  1. bigjonny9
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    bigjonny9 Junior Member

    hey guys, I have a Bertram 20 moppie that I’m refitting. I’ve always been a fan of the Bertram 20s. I’ve noticed that the main chine on my berty has a slight rise about 2/3 ft before the transom. It’s only on the main chine. The chine is also reversed. The others below just continue aft in a pretty fair line. The topsides aft of midships also have a nice bit of tumbleholme which I think adds to the appeal. My question is why the rise in the main chine as it’s progressing aft?. What purpose does this serve? I’ve heard that the Bertram 20s can do a little porpoising. Is that the reason? I’m asking as I’m genuinely curious and I’m also taking the diesel inboard out and I’m building a pod to hold a 250hp four stroke and I’m wondering wether to take this into account. I will be running the pod directly from the hull lines and continuing the same deadrise right through. Thank you for your responses
     

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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    I don't recall seeing one looking like that.
     
  3. bigjonny9
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    bigjonny9 Junior Member

    Sorry what do you mean?
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    I mean I've never seen that kick-up at the chine aft. Any other pics ?
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    I'm thinking someone might have made a modification to try and accomodate a diesel sterndrive
     
  6. bigjonny9
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    bigjonny9 Junior Member

    Sure
     

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  7. bigjonny9
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    bigjonny9 Junior Member

    Dosnt look like it unless it was down in the mould it’s wasn’t a custom. But I will have another look there’s definitely been some smaller mods like the bow sprite
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    Might be nothing to it, perhaps an optical illusion caused by the angle the pic taken from, The one with the blue stripe is the same boat ?
     
  9. bigjonny9
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    bigjonny9 Junior Member

    Yeah I’ve just stripped it. If you want another photo just tell me what angle and I’ll take it. It’s definitely there. And it’s moulded . I’ve got the floor up and there no sign of work done.
     
  10. bigjonny9
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    bigjonny9 Junior Member

    It’s in all
    The Bertram 20s
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    I can't say I have ever noticed it, like you can notice the hook ouitboard of the outside strake in for example, a Formula 233. That old 20 footer was made in a split mould, later one may different. But I don't think the chine is straight aft on that one, it narrows a little at the transom, if I recall correctly
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    No sign of that irregularity with this, one, which also appears to be from a split mould, judging by the projecting chine flat. Bertram.jpg
     
  13. bigjonny9
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    bigjonny9 Junior Member

    Yeah that’s strange I’ve tried to take a photo from the same angle
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    Could it be that the stringers are shot, or you have removed them as part of this project, and the trailer rollers are deforming the bottom aft ?
     

  15. bigjonny9
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    bigjonny9 Junior Member

    No the stringers are all glass. I haven removed them ive just taken up the sole . And it’s a solid glass hull. No movement in the hull that’s the shape.
     
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